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| author | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-10-30 11:06:03 -0700 |
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| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-10-30 11:06:03 -0700 |
| commit | 482878a1a7758221a34413944e9139104ed487ee (patch) | |
| tree | ef430810f4d7f89a95852b11f29f1449a48f5033 /0001-kdbus-add-documentation.patch | |
| parent | 210d894ff19726f6463e0fc1afbb3f6662d18e33 (diff) | |
| download | patches-482878a1a7758221a34413944e9139104ed487ee.tar.gz | |
kdbus and pci patches added
Diffstat (limited to '0001-kdbus-add-documentation.patch')
| -rw-r--r-- | 0001-kdbus-add-documentation.patch | 1839 |
1 files changed, 1839 insertions, 0 deletions
diff --git a/0001-kdbus-add-documentation.patch b/0001-kdbus-add-documentation.patch new file mode 100644 index 00000000000000..a4c8025219c760 --- /dev/null +++ b/0001-kdbus-add-documentation.patch @@ -0,0 +1,1839 @@ +From 53f7cb9ca49d8a62cfc4c9740ffb34068c1599a6 Mon Sep 17 00:00:00 2001 +From: Daniel Mack <daniel@zonque.org> +Date: Thu, 11 Sep 2014 21:50:47 +0200 +Subject: [PATCH 01/12] kdbus: add documentation + +From: Daniel Mack <daniel@zonque.org> + +kdbus is a system for low-latency, low-overhead, easy to use +interprocess communication (IPC). + +The interface to all functions in this driver is implemented through ioctls +on /dev nodes. This patch adds detailed documentation about the kernel +level API design. + +Signed-off-by: Daniel Mack <daniel@zonque.org> +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + Documentation/kdbus.txt | 1815 ++++++++++++++++++++++++++++++++++++++++++++++++ + 1 file changed, 1815 insertions(+) + create mode 100644 Documentation/kdbus.txt + +--- /dev/null ++++ b/Documentation/kdbus.txt +@@ -0,0 +1,1815 @@ ++D-Bus is a system for powerful, easy to use interprocess communication (IPC). ++ ++The focus of this document is an overview of the low-level, native kernel D-Bus ++transport called kdbus. Kdbus in the kernel acts similar to a device driver, ++all communication between processes take place over special character device ++nodes in /dev/kdbus/. ++ ++For the general D-Bus protocol specification, the payload format, the ++marshaling, and the communication semantics, please refer to: ++ http://dbus.freedesktop.org/doc/dbus-specification.html ++ ++For a kdbus specific userspace library implementation please refer to: ++ http://cgit.freedesktop.org/systemd/systemd/tree/src/systemd/sd-bus.h ++ ++Articles about D-Bus and kdbus: ++ http://lwn.net/Articles/580194/ ++ ++ ++1. Terminology ++=============================================================================== ++ ++ Domain: ++ A domain is a named object containing a number of buses. A system ++ container that contains its own init system and users usually also ++ runs in its own kdbus domain. The /dev/kdbus/domain/<container-name>/ ++ directory shows up inside the domain as /dev/kdbus/. Every domain offers ++ its own "control" device node to create new buses or new sub-domains. ++ Domains have no connection to each other and cannot see nor talk to ++ each other. See section 5 for more details. ++ ++ Bus: ++ A bus is a named object inside a domain. Clients exchange messages ++ over a bus. Multiple buses themselves have no connection to each other; ++ messages can only be exchanged on the same bus. The default entry point to ++ a bus, where clients establish the connection to, is the "bus" device node ++ /dev/kdbus/<bus name>/bus. ++ Common operating system setups create one "system bus" per system, and one ++ "user bus" for every logged-in user. Applications or services may create ++ their own private named buses. See section 5 for more details. ++ ++ Endpoint: ++ An endpoint provides the device node to talk to a bus. Opening an ++ endpoint creates a new connection to the bus to which the endpoint belongs. ++ Every bus has a default endpoint called "bus". ++ A bus can optionally offer additional endpoints with custom names to ++ provide a restricted access to the same bus. Custom endpoints carry ++ additional policy which can be used to give sandboxed processes only ++ a locked-down, limited, filtered access to the same bus. ++ See section 5 for more details. ++ ++ Connection: ++ A connection to a bus is created by opening an endpoint device node of ++ a bus and becoming an active client with the HELLO exchange. Every ++ connected client connection has a unique identifier on the bus and can ++ address messages to every other connection on the same bus by using ++ the peer's connection id as the destination. ++ See section 6 for more details. ++ ++ Pool: ++ Each connection allocates a piece of shmem-backed memory that is used ++ to receive messages and answers to ioctl command from the kernel. It is ++ never used to send anything to the kernel. In order to access that memory, ++ userspace must mmap() it into its task. ++ See section 12 for more details. ++ ++ Well-known Name: ++ A connection can, in addition to its implicit unique connection id, request ++ the ownership of a textual well-known name. Well-known names are noted in ++ reverse-domain notation, such as com.example.service1. Connections offering ++ a service on a bus are usually reached by its well-known name. The analogy ++ of connection id and well-known name is an IP address and a DNS name ++ associated with that address. ++ ++ Message: ++ Connections can exchange messages with other connections by addressing ++ the peers with their connection id or well-known name. A message consists ++ of a message header with kernel-specific information on how to route the ++ message, and the message payload, which is a logical byte stream of ++ arbitrary size. Messages can carry additional file descriptors to be passed ++ from one connection to another. Every connection can specify which set of ++ metadata the kernel should attach to the message when it is delivered ++ to the receiving connection. Metadata contains information like: system ++ timestamps, uid, gid, tid, proc-starttime, well-known-names, process comm, ++ process exe, process argv, cgroup, capabilities, seclabel, audit session, ++ loginuid and the connection's human-readable name. ++ See section 7 and 13 for more details. ++ ++ Item: ++ The API of kdbus implements a notion of items, submitted through and ++ returned by most ioctls, and stored inside data structures in the ++ connection's pool. See section 4 for more details. ++ ++ Broadcast and Match: ++ Broadcast messages are potentially sent to all connections of a bus. By ++ default, the connections will not actually receive any of the sent ++ broadcast messages; only after installing a match for specific message ++ properties, a broadcast message passes this filter. ++ See section 10 for more details. ++ ++ Policy: ++ A policy is a set of rules that define which connections can see, talk to, ++ or register a well-know name on the bus. A policy is attached to buses and ++ custom endpoints, and modified by policy holder connection or owners of ++ custom endpoints. See section 11 for more details. ++ ++ Access rules to allow who can see a name on the bus are only checked on ++ custom endpoints. Policies may be defined with names that end with '.*'. ++ When matching a well-known name against such a wildcard entry, the last ++ part of the name is ignored and checked against the wildcard name without ++ the trailing '.*'. See section 11 for more details. ++ ++ Privileged bus users: ++ A user connecting to the bus is considered privileged if it is either the ++ creator of the bus, or if it has the CAP_IPC_OWNER capability flag set. ++ ++ ++2. Device Node Layout ++=============================================================================== ++ ++The kdbus interface is exposed through device nodes in /dev. ++ ++ /sys/bus/kdbus ++ `-- devices ++ |-- kdbus!0-system!bus -> ../../../devices/virtual/kdbus/kdbus!0-system!bus ++ |-- kdbus!2702-user!bus -> ../../../devices/virtual/kdbus/kdbus!2702-user!bus ++ |-- kdbus!2702-user!ep.app -> ../../../devices/virtual/kdbus/kdbus!2702-user!ep.app ++ `-- kdbus!control -> ../../../devices/kdbus!control ++ ++ /dev/kdbus ++ |-- control ++ |-- 0-system ++ | |-- bus ++ | `-- ep.apache ++ |-- 1000-user ++ | `-- bus ++ |-- 2702-user ++ | |-- bus ++ | `-- ep.app ++ `-- domain ++ |-- fedoracontainer ++ | |-- control ++ | |-- 0-system ++ | | `-- bus ++ | `-- 1000-user ++ | `-- bus ++ `-- mydebiancontainer ++ |-- control ++ `-- 0-system ++ `-- bus ++ ++Note: ++ The device node subdirectory layout is arranged that a future version of ++ kdbus could be implemented as a file system with a separate instance mounted ++ for each domain. For any future changes, this always needs to be kept ++ in mind. Also the dependency on udev's userspace hookups or sysfs attribute ++ use should be limited to the absolute minimum for the same reason. ++ ++ ++3. Data Structures and flags ++=============================================================================== ++ ++3.1 Data structures and interconnections ++---------------------------------------- ++ ++ +-------------------------------------------------------------------------+ ++ | Domain (Init Domain) | ++ | /dev/kdbus/control | ++ | +---------------------------------------------------------------------+ | ++ | | Bus (System Bus) | | ++ | | /dev/kdbus/0-system/ | | ++ | | +-------------------------------+ +-------------------------------+ | | ++ | | | Endpoint | | Endpoint | | | ++ | | | /dev/kdbus/0-system/bus | | /dev/kdbus/0-system/ep.app | | | ++ | | +-------------------------------+ +-------------------------------+ | | ++ | | +--------------+ +--------------+ +--------------+ +--------------+ | | ++ | | | Connection | | Connection | | Connection | | Connection | | | ++ | | | :1.22 | | :1.25 | | :1.55 | | :1.81 | | | ++ | | +--------------+ +--------------+ +--------------+ +--------------+ | | ++ | +---------------------------------------------------------------------+ | ++ | | ++ | +---------------------------------------------------------------------+ | ++ | | Bus (User Bus for UID 2702) | | ++ | | /dev/kdbus/2702-user/ | | ++ | | +-------------------------------+ +-------------------------------+ | | ++ | | | Endpoint | | Endpoint | | | ++ | | | /dev/kdbus/2702-user/bus | | /dev/kdbus/2702-user/ep.app | | | ++ | | +-------------------------------+ +-------------------------------+ | | ++ | | +--------------+ +--------------+ +--------------+ +--------------+ | | ++ | | | Connection | | Connection | | Connection | | Connection | | | ++ | | | :1.22 | | :1.25 | | :1.55 | | :1.81 | | | ++ | | +--------------+ +--------------+ +-------------------------------+ | | ++ | +---------------------------------------------------------------------+ | ++ | | ++ | +---------------------------------------------------------------------+ | ++ | | Domain (Container; inside it, fedoracontainer/ becomes /dev/kdbus/) | | ++ | | /dev/kdbus/domain/fedoracontainer/control | | ++ | | +-----------------------------------------------------------------+ | | ++ | | | Bus (System Bus of "fedoracontainer") | | | ++ | | | /dev/kdbus/domain/fedoracontainer/0-system/ | | | ++ | | | +-----------------------------+ | | | ++ | | | | Endpoint | | | | ++ | | | | /dev/.../0-system/bus | | | | ++ | | | +-----------------------------+ | | | ++ | | | +-------------+ +-------------+ | | | ++ | | | | Connection | | Connection | | | | ++ | | | | :1.22 | | :1.25 | | | | ++ | | | +-------------+ +-------------+ | | | ++ | | +-----------------------------------------------------------------+ | | ++ | | | | ++ | | +-----------------------------------------------------------------+ | | ++ | | | Bus (User Bus for UID 270 of "fedoracontainer") | | | ++ | | | /dev/kdbus/domain/fedoracontainer/2702-user/ | | | ++ | | | +-----------------------------+ | | | ++ | | | | Endpoint | | | | ++ | | | | /dev/.../2702-user/bus | | | | ++ | | | +-----------------------------+ | | | ++ | | | +-------------+ +-------------+ | | | ++ | | | | Connection | | Connection | | | | ++ | | | | :1.22 | | :1.25 | | | | ++ | | | +-------------+ +-------------+ | | | ++ | | +-----------------------------------------------------------------+ | | ++ | +---------------------------------------------------------------------+ | ++ +-------------------------------------------------------------------------+ ++ ++The above description uses the D-Bus notation of unique connection names that ++adds a ":1." prefix to the connection's unique ID. kbus itself doesn't ++use that notation, neither internally nor externally. However, libraries and ++other usespace code that aims for compatibility to D-Bus might. ++ ++3.2 Flags ++--------- ++ ++All ioctls used in the communication with the driver contain two 64-bit fields, ++'flags' and 'kernel_flags'. In 'flags', the behavior of the command can be ++tweaked, whereas in 'kernel_flags', the kernel driver writes back the mask of ++supported bits upon each call, and sets the KDBUS_FLAGS_KERNEL bit. This is a ++way to probe possible kernel features and make code forward and backward ++compatible. ++ ++All bits that are not recognized by the kernel in 'flags' are rejected, and the ++ioctl fails with -EINVAL. ++ ++ ++4. Items ++=============================================================================== ++ ++To flexibly augment transport structures used by kdbus, data blobs of type ++struct kdbus_item are used. An item has a fixed-sized header that only stores ++the type of the item and the overall size. The total size is variable and is ++in some cases defined by the item type, in other cases, they can be of ++arbitrary length (for instance, a string). ++ ++In the external kernel API, items are used for many ioctls to transport ++optional information from userspace to kernelspace. They are also used for ++information stored in a connection's pool, such as messages, name lists or ++requested connection information. ++ ++In all such occasions where items are used as part of the kdbus kernel API, ++they are embedded in structs that have an overall size of their own, so there ++can be many of them. ++ ++The kernel expects all items to be aligned to 8-byte boundaries. ++ ++A simple iterator in userspace would iterate over the items until the items ++have reached the embedding structure's overall size. An example implementation ++of such an iterator can be found in tools/testing/selftests/kdbus/kdbus-util.h. ++ ++ ++5. Creation of new domains, buses and endpoints ++=============================================================================== ++ ++The initial kdbus domain is unconditionally created by the kernel module. A ++domain contains a "control" device node which allows to create a new bus or ++domain. New domains do not have any buses created by default. ++ ++ ++5.1 Domains and buses ++--------------------- ++ ++Opening the control device node returns a file descriptor, it accepts the ++ioctls KDBUS_CMD_BUS_MAKE and KDBUS_CMD_DOMAIN_MAKE which specify the name of ++the new bus or domain to create. The control file descriptor needs to be kept ++open for the entire life-time of the created bus or domain, closing it will ++immediately cleanup the entire bus or domain and all its associated ++resources and connections. Every control file descriptor can only be used once ++to create a new bus or domain; from that point, it is not used for any ++further communication until the final close(). ++ ++Each bus will generate a random, 128-bit UUID upon creation. It will be ++returned to the creators of connections through kdbus_cmd_hello.id128 and can ++be used by userspace to uniquely identify buses, even across different machines ++or containers. The UUID will have its its variant bits set to 'DCE', and denote ++version 4 (random). ++ ++When a new domain is created, its structure in /dev/kdbus/<name>/ is a ++replication of what's initially created in /dev/kdbus. In fact, internally, ++a dummy default domain is set up when the driver is loaded. This allows ++userspace to bind-mount domain subtrees of /dev/kdbus into a container's ++filesystem view, and hence achieve complete isolation from the host's domain ++and those of other containers. ++ ++ ++5.2 Endpoints ++------------- ++ ++Endpoints are entry points to a bus. By default, each bus has a default ++endpoint called 'bus'. The bus owner has the ability to create custom ++endpoints with specific names, permissions, and policy databases (see below). ++ ++To create a custom endpoint, use the KDBUS_CMD_ENDPOINT_MAKE ioctl with struct ++kdbus_cmd_make. Custom endpoints always have a policy db that, by default, ++does not allow anything. Everything that users of this new endpoint should be ++able to do has to be explicitly specified through KDBUS_ITEM_NAME and ++KDBUS_ITEM_POLICY_ACCESS items. ++ ++5.3 Creating domains, buses and endpoints ++----------------------------------------- ++ ++KDBUS_CMD_BUS_MAKE, KDBUS_CMD_DOMAIN_MAKE and KDBUS_CMD_ENDPOINT_MAKE take a ++struct kdbus_cmd_make argument. ++ ++struct kdbus_cmd_make { ++ __u64 size; ++ The overall size of the struct, including its items. ++ ++ __u64 flags; ++ The flags for creation. ++ ++ KDBUS_MAKE_ACCESS_GROUP ++ Make the device node group-accessible ++ ++ KDBUS_MAKE_ACCESS_WORLD ++ Make the device node world-accessible ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ struct kdbus_item items[0]; ++ A list of items, only used for creating custom endpoints. Ignored for ++ buses and domains. ++}; ++ ++ ++6. Connections ++=============================================================================== ++ ++ ++6.1 Connection IDs and well-known connection names ++-------------------------------------------------- ++ ++Connections are identified by their connection id, internally implemented as a ++uint64_t counter. The IDs of every newly created bus start at 1, and every new ++connection will increment the counter by 1. The ids are not reused. ++ ++In higher level tools, the user visible representation of a connection is ++defined by the D-Bus protocol specification as ":1.<id>". ++ ++Messages with a specific uint64_t destination id are directly delivered to ++the connection with the corresponding id. Messages with the special destination ++id KDBUS_DST_ID_BROADCAST are broadcast messages and are potentially delivered ++to all known connections on the bus; clients interested in broadcast messages ++need to subscribe to the specific messages they are interested though, before ++any broadcast message reaches them. ++ ++Messages synthesized and sent directly by the kernel will carry the special ++source id KDBUS_SRC_ID_KERNEL (0). ++ ++In addition to the unique uint64_t connection id, established connections can ++request the ownership of well-known names, under which they can be found and ++addressed by other bus clients. A well-known name is associated with one and ++only one connection at a time. See section 8 on name acquisition and the ++name registry, and the validity of names. ++ ++Messages can specify the special destination id 0 and carry a well-known name ++in the message data. Such a message is delivered to the destination connection ++which owns that well-known name. ++ ++ +-------------------------------------------------------------------------+ ++ | +---------------+ +---------------------------+ | ++ | | Connection | | Message | -----------------+ | ++ | | :1.22 | --> | src: 22 | | | ++ | | | | dst: 25 | | | ++ | | | | | | | ++ | | | | | | | ++ | | | +---------------------------+ | | ++ | | | | | ++ | | | <--------------------------------------+ | | ++ | +---------------+ | | | ++ | | | | ++ | +---------------+ +---------------------------+ | | | ++ | | Connection | | Message | -----+ | | ++ | | :1.25 | --> | src: 25 | | | ++ | | | | dst: 0xffffffffffffffff | -------------+ | | ++ | | | | (KDBUS_DST_ID_BROADCAST) | | | | ++ | | | | | ---------+ | | | ++ | | | +---------------------------+ | | | | ++ | | | | | | | ++ | | | <--------------------------------------------------+ | ++ | +---------------+ | | | ++ | | | | ++ | +---------------+ +---------------------------+ | | | ++ | | Connection | | Message | --+ | | | ++ | | :1.55 | --> | src: 55 | | | | | ++ | | | | dst: 0 / org.foo.bar | | | | | ++ | | | | | | | | | ++ | | | | | | | | | ++ | | | +---------------------------+ | | | | ++ | | | | | | | ++ | | | <------------------------------------------+ | | ++ | +---------------+ | | | ++ | | | | ++ | +---------------+ | | | ++ | | Connection | | | | ++ | | :1.81 | | | | ++ | | org.foo.bar | | | | ++ | | | | | | ++ | | | | | | ++ | | | <-----------------------------------+ | | ++ | | | | | ++ | | | <----------------------------------------------+ | ++ | +---------------+ | ++ +-------------------------------------------------------------------------+ ++ ++ ++6.2 Creating connections ++------------------------ ++ ++A connection to a bus is created by opening an endpoint device node of ++a bus and becoming an active client with the KDBUS_CMD_HELLO ioctl. Every ++connected client connection has a unique identifier on the bus and can ++address messages to every other connection on the same bus by using ++the peer's connection id as the destination. ++ ++The KDBUS_CMD_HELLO ioctl takes the following struct as argument. ++ ++struct kdbus_cmd_hello { ++ __u64 size; ++ The overall size of the struct, including all attached items. ++ ++ __u64 conn_flags; ++ Flags to apply to this connection: ++ ++ KDBUS_HELLO_ACCEPT_FD ++ When this flag is set, the connection can be sent file descriptors ++ as message payload. If it's not set, any attempt of doing so will ++ result in -ECOMM on the sender's side. ++ ++ KDBUS_HELLO_ACTIVATOR ++ Make this connection an activator (see below). With this bit set, ++ an item of type KDBUS_ITEM_NAME has to be attached which describes ++ the well-known name this connection should be an activator for. ++ ++ KDBUS_HELLO_POLICY_HOLDER ++ Make this connection a policy holder (see below). With this bit set, ++ an item of type KDBUS_ITEM_NAME has to be attached which describes ++ the well-known name this connection should hold a policy for. ++ ++ KDBUS_HELLO_MONITOR ++ Make this connection an eaves-dropping connection that receives all ++ unicast messages sent on the bus. To also receive broadcast messages, ++ the connection has to upload appropriate matches as well. ++ This flag is only valid for privileged bus connections. ++ ++ __u64 attach_flags; ++ Request the attachment of metadata for each message received by this ++ connection. The metadata actually attached may actually augment the list ++ of requested items. See section 13 for more details. ++ ++ __u64 bus_flags; ++ Upon successful completion of the ioctl, this member will contain the ++ flags of the bus it connected to. ++ ++ __u64 id; ++ Upon successful completion of the ioctl, this member will contain the ++ id of the new connection. ++ ++ __u64 pool_size; ++ The size of the communication pool, in bytes. The pool can be accessed ++ by calling mmap() on the file descriptor that was used to issue the ++ KDBUS_CMD_HELLO ioctl. ++ ++ struct kdbus_bloom_parameter bloom; ++ Bloom filter parameter (see below). ++ ++ __u8 id128[16]; ++ Upon successful completion of the ioctl, this member will contain the ++ 128 bit wide UUID of the connected bus. ++ ++ struct kdbus_item items[0]; ++ Variable list of items to add optional additional information. The ++ following items are currently expected/valid: ++ ++ KDBUS_ITEM_CONN_NAME ++ Contains a string to describes this connection's name, so it can be ++ identified later. ++ ++ KDBUS_ITEM_NAME ++ KDBUS_ITEM_POLICY_ACCESS ++ For activators and policy holders only, combinations of these two ++ items describe policy access entries (see section about policy db). ++ ++ KDBUS_ITEM_CREDS ++ KDBUS_ITEM_SECLABEL ++ Privileged bus users may submit these types in order to create ++ connections with faked credentials. The only real use case for this ++ is a proxy service which acts on behalf of some other tasks. For a ++ connection that runs in that mode, the message's metadata items will ++ be limited to what's specified here. See section 13 for more ++ information. ++ ++ Items of other types are silently ignored. ++}; ++ ++ ++6.3 Activator and policy holder connection ++------------------------------------------ ++ ++An activator connection is a placeholder for a well-known name. Messages sent ++to such a connection can be used by userspace to start an implementor ++connection, which will then get all the messages from the activator copied ++over. An activator connection cannot be used to send any message. ++ ++A policy holder connection only installs a policy for one or more names. ++These policy entries are kept active as long as the connection is alive, and ++are removed once it terminates. Such a policy connection type can be used to ++deploy restrictions for names that are not yet active on the bus. A policy ++holder connection cannot be used to send any message. ++ ++The creation of activator, policy holder or monitor connections is an operation ++restricted to privileged users on the bus (see section "Terminology"). ++ ++ ++6.4 Retrieving information on a connection ++------------------------------------------ ++ ++The KDBUS_CMD_CONN_INFO ioctl can be used to retrieve credentials and ++properties of the initial creator of a connection. This ioctl uses the ++following struct: ++ ++struct kdbus_cmd_info { ++ __u64 size; ++ The overall size of the struct, including the name with its 0-byte string ++ terminator. ++ ++ __u64 flags; ++ Specify which items should be attached to the answer. ++ The following flags can be used: ++ ++ KDBUS_ATTACH_NAMES ++ Add an item to the answer containing all the names the connection ++ currently owns. ++ ++ KDBUS_ATTACH_CONN_NAME ++ Add an item to the answer containing the connection's name. ++ ++ After the ioctl returns, this field will contain the current metadata ++ attach flags of the connection. ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ __u64 id; ++ The connection's numerical ID to retrieve information for. If set to ++ non-zero value, the 'name' field is ignored. ++ ++ __u64 offset; ++ When the ioctl returns, this value will yield the offset of the connection ++ information inside the caller's pool. ++ ++ struct kdbus_item items[0]; ++ The optional item list, containing the well-known name to look up as ++ a KDBUS_ITEM_NAME. Only required if the 'id' field is set to 0. ++ All other items are currently ignored. ++}; ++ ++After the ioctl returns, the following struct will be stored in the caller's ++pool at 'offset'. ++ ++struct kdbus_info { ++ __u64 size; ++ The overall size of the struct, including all its items. ++ ++ __u64 id; ++ The connection's unique ID. ++ ++ __u64 flags; ++ The connection's flags as specified when it was created. ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ struct kdbus_item items[0]; ++ Depending on the 'flags' field in struct kdbus_cmd_info, items of ++ types KDBUS_ITEM_NAME and KDBUS_ITEM_CONN_NAME are followed here. ++}; ++ ++Once the caller is finished with parsing the return buffer, it needs to call ++KDBUS_CMD_FREE for the offset. ++ ++ ++6.5 Getting information about a connection's bus creator ++-------------------------------------------------------- ++ ++The KDBUS_CMD_BUS_CREATOR_INFO ioctl takes the same struct as ++KDBUS_CMD_CONN_INFO but is used to retrieve information about the creator of ++the bus the connection is attached to. The metadata returned by this call is ++collected during the creation of the bus and is never altered afterwards, so ++it provides pristine information on the task that created the bus, at the ++moment when it did so. ++ ++In response to this call, a slice in the connection's pool is allocated and ++filled with an object of type struct kdbus_info, pointed to by the ioctl's ++'offset' field. ++ ++struct kdbus_info { ++ __u64 size; ++ The overall size of the struct, including all its items. ++ ++ __u64 id; ++ The bus' ID ++ ++ __u64 flags; ++ The bus' flags as specified when it was created. ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ struct kdbus_item items[0]; ++ Metadata information is stored in items here. ++}; ++ ++Once the caller is finished with parsing the return buffer, it needs to call ++KDBUS_CMD_FREE for the offset. ++ ++ ++6.6 Updating connection details ++------------------------------- ++ ++Some of a connection's details can be updated with the KDBUS_CMD_CONN_UPDATE ++ioctl, using the file descriptor that was used to create the connection. ++The update command uses the following struct. ++ ++struct kdbus_cmd_update { ++ __u64 size; ++ The overall size of the struct, including all its items. ++ ++ struct kdbus_item items[0]; ++ Items to describe the connection details to be updated. The following item ++ types are supported: ++ ++ KDBUS_ITEM_ATTACH_FLAGS ++ Supply a new set of items to be attached to each message. ++ ++ KDBUS_ITEM_NAME ++ KDBUS_ITEM_POLICY_ACCESS ++ Policy holder connections may supply a new set of policy information ++ with these items. For other connection types, -EOPNOTSUPP is returned. ++}; ++ ++ ++6.6 Termination ++--------------- ++ ++A connection can be terminated by simply closing the file descriptor that was ++used to start the connection. All pending incoming messages will be discarded, ++and the memory in the pool will be freed. ++ ++An alternative way of way of closing down a connection is calling the ++KDBUS_CMD_BYEBYE ioctl on it, which will only succeed if the message queue ++of the connection is empty at the time of closing, otherwise, -EBUSY is ++returned. ++ ++When this ioctl returns successfully, the connection has been terminated and ++won't accept any new messages from remote peers. This way, a connection can ++be terminated race-free, without losing any messages. ++ ++ ++7. Messages ++=============================================================================== ++ ++Messages consist of a fixed-size header followed directly by a list of ++variable-sized data 'items'. The overall message size is specified in the ++header of the message. The chain of data items can contain well-defined ++message metadata fields, raw data, references to data, or file descriptors. ++ ++ ++7.1 Sending messages ++-------------------- ++ ++Messages are passed to the kernel with the KDBUS_CMD_MSG_SEND ioctl. Depending ++on the the destination address of the message, the kernel delivers the message ++to the specific destination connection or to all connections on the same bus. ++Sending messages across buses is not possible. Messages are always queued in ++the memory pool of the destination connection (see below). ++ ++The KDBUS_CMD_MSG_SEND ioctl uses struct kdbus_msg to describe the message to ++be sent. ++ ++struct kdbus_msg { ++ __u64 size; ++ The over all size of the struct, including the attached items. ++ ++ __u64 flags; ++ Flags for message delivery: ++ ++ KDBUS_MSG_FLAGS_EXPECT_REPLY ++ Expect a reply from the remote peer to this message. With this bit set, ++ the timeout_ns field must be set to a non-zero number of nanoseconds in ++ which the receiving peer is expected to reply. If such a reply is not ++ received in time, the sender will be notified with a timeout message ++ (see below). The value must be an absolute value, in nanoseconds and ++ based on CLOCK_MONOTONIC. ++ ++ For a message to be accepted as reply, it must be a direct message to ++ the original sender (not a broadcast), and its kdbus_msg.reply_cookie ++ must match the previous message's kdbus_msg.cookie. ++ ++ Expected replies also temporarily open the policy of the sending ++ connection, so the other peer is allowed to respond within the given ++ time window. ++ ++ KDBUS_MSG_FLAGS_SYNC_REPLY ++ By default, all calls to kdbus are considered asynchronous, ++ non-blocking. However, as there are many use cases that need to wait ++ for a remote peer to answer a method call, there's a way to send a ++ message and wait for a reply in a synchronous fashion. This is what ++ the KDBUS_MSG_FLAGS_SYNC_REPLY controls. The KDBUS_CMD_MSG_SEND ioctl ++ will block until the reply has arrived, the timeout limit is reached, ++ in case the remote connection was shut down, or if interrupted by ++ a signal before any reply; see signal(7). ++ ++ The offset of the reply message in the sender's pool is stored in ++ in 'offset_reply' when the ioctl has returned without error. Hence, ++ there is no need for another KDBUS_CMD_MSG_RECV ioctl or anything else ++ to receive the reply. ++ ++ KDBUS_MSG_FLAGS_NO_AUTO_START ++ By default, when a message is sent to an activator connection, the ++ activator notified and will start an implementor. This flag inhibits ++ that behavior. With this bit set, and the remote being an activator, ++ -EADDRNOTAVAIL is returned from the ioctl. ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call of ++ KDBUS_MSG_SEND. ++ ++ __s64 priority; ++ The priority of this message. Receiving messages (see below) may ++ optionally be constrained to messages of a minimal priority. This ++ allows for use cases where timing critical data is interleaved with ++ control data on the same connection. If unused, the priority should be ++ set to zero. ++ ++ __u64 dst_id; ++ The numeric ID of the destination connection, or KDBUS_DST_ID_BROADCAST ++ (~0ULL) to address every peer on the bus, or KDBUS_DST_ID_NAME (0) to look ++ it up dynamically from the bus' name registry. In the latter case, an item ++ of type KDBUS_ITEM_DST_NAME is mandatory. ++ ++ __u64 src_id; ++ Upon return of the ioctl, this member will contain the sending ++ connection's numerical ID. Should be 0 at send time. ++ ++ __u64 payload_type; ++ Type of the payload in the actual data records. Currently, only ++ KDBUS_PAYLOAD_DBUS is accepted as input value of this field. When ++ receiving messages that are generated by the kernel (notifications), ++ this field will yield KDBUS_PAYLOAD_KERNEL. ++ ++ __u64 cookie; ++ Cookie of this message, for later recognition. Also, when replying ++ to a message (see above), the cookie_reply field must match this value. ++ ++ __u64 timeout_ns; ++ If the message sent requires a reply from the remote peer (see above), ++ this field contains the timeout in absolute nanoseconds based on ++ CLOCK_MONOTONIC. ++ ++ __u64 cookie_reply; ++ If the message sent is a reply to another message, this field must ++ match the cookie of the formerly received message. ++ ++ __u64 offset_reply; ++ If the message successfully got a synchronous reply (see above), this ++ field will yield the offset of the reply message in the sender's pool. ++ Is is what KDBUS_CMD_MSG_RECV usually does for asynchronous messages. ++ ++ struct kdbus_item items[0]; ++ A dynamically sized list of items to contain additional information. ++ The following items are expected/valid: ++ ++ KDBUS_ITEM_PAYLOAD_VEC ++ KDBUS_ITEM_PAYLOAD_MEMFD ++ KDBUS_ITEM_FDS ++ Actual data records containing the payload. See section "Passing of ++ Payload Data". ++ ++ KDBUS_ITEM_BLOOM_FILTER ++ Bloom filter for matches (see below). ++ ++ KDBUS_ITEM_DST_NAME ++ Well-known name to send this message to. Required if dst_id is set ++ to KDBUS_DST_ID_NAME. If a connection holding the given name can't ++ be found, -ESRCH is returned. ++ For messages to a unique name (ID), this item is optional. If present, ++ the kernel will make sure the name owner matches the given unique name. ++ This allows userspace tie the message sending to the condition that a ++ name is currently owned by a certain unique name. ++}; ++ ++The message will be augmented by the requested metadata items when queued into ++the receiver's pool. See also section 13.1 ("Metadata and namespaces"). ++ ++ ++7.2 Message layout ++------------------ ++ ++The layout of a message is shown below. ++ ++ +-------------------------------------------------------------------------+ ++ | Message | ++ | +---------------------------------------------------------------------+ | ++ | | Header | | ++ | | size: overall message size, including the data records | | ++ | | destination: connection id of the receiver | | ++ | | source: connection id of the sender (set by kernel) | | ++ | | payload_type: "DBusDBus" textual identifier stored as uint64_t | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | Data Record | | ++ | | size: overall record size (without padding) | | ++ | | type: type of data | | ++ | | data: reference to data (address or file descriptor) | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | padding bytes to the next 8 byte alignment | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | Data Record | | ++ | | size: overall record size (without padding) | | ++ | | ... | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | padding bytes to the next 8 byte alignment | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | Data Record | | ++ | | size: overall record size | | ++ | | ... | | ++ | +---------------------------------------------------------------------+ | ++ | +---------------------------------------------------------------------+ | ++ | | padding bytes to the next 8 byte alignment | | ++ | +---------------------------------------------------------------------+ | ++ +-------------------------------------------------------------------------+ ++ ++ ++7.3 Passing of Payload Data ++--------------------------- ++ ++When connecting to the bus, receivers request a memory pool of a given size, ++large enough to carry all backlog of data enqueued for the connection. The ++pool is internally backed by a shared memory file which can be mmap()ed by ++the receiver. ++ ++KDBUS_MSG_PAYLOAD_VEC: ++ Messages are directly copied by the sending process into the receiver's pool, ++ that way two peers can exchange data by effectively doing a single-copy from ++ one process to another, the kernel will not buffer the data anywhere else. ++ ++KDBUS_MSG_PAYLOAD_MEMFD: ++ Messages can reference memfd files which contain the data. ++ memfd files are tmpfs-backed files that allow sealing of the content of the ++ file, which prevents all writable access to the file content. ++ Only sealed memfd files are accepted as payload data, which enforces ++ reliable passing of data; the receiver can assume that neither the sender nor ++ anyone else can alter the content after the message is sent. ++ ++Apart from the sender filling-in the content into memfd files, the data will ++be passed as zero-copy from one process to another, read-only, shared between ++the peers. ++ ++ ++7.4 Receiving messages ++---------------------- ++ ++Messages are received by the client with the KDBUS_CMD_MSG_RECV ioctl. The ++endpoint device node of the bus supports poll() to wake up the receiving ++process when new messages are queued up to be received. ++ ++With the KDBUS_CMD_MSG_RECV ioctl, a struct kdbus_cmd_recv is used. ++ ++struct kdbus_cmd_recv { ++ __u64 flags; ++ Flags to control the receive command. ++ ++ KDBUS_RECV_PEEK ++ Just return the location of the next message. Do not install file ++ descriptors or anything else. This is usually used to determine the ++ sender of the next queued message. ++ ++ KDBUS_RECV_DROP ++ Drop the next message without doing anything else with it, and free the ++ pool slice. This a short-cut for KDBUS_RECV_PEEK and KDBUS_CMD_FREE. ++ ++ KDBUS_RECV_USE_PRIORITY ++ Use the priority field (see below). ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ __s64 priority; ++ With KDBUS_RECV_USE_PRIORITY set in flags, receive the next message in ++ the queue with at least the given priority. If no such message is waiting ++ in the queue, -ENOMSG is returned. ++ ++ __u64 offset; ++ Upon return of the ioctl, this field contains the offset in the ++ receiver's memory pool. ++}; ++ ++Unless KDBUS_RECV_DROP was passed, and given that the ioctl succeeded, the ++offset field contains the location of the new message inside the receiver's ++pool. The message is stored as struct kdbus_msg at this offset, and can be ++interpreted with the semantics described above. ++ ++Also, if the connection allowed for file descriptor to be passed ++(KDBUS_HELLO_ACCEPT_FD), and if the message contained any, they will be ++installed into the receiving process after the KDBUS_CMD_MSG_RECV ioctl ++returns. The receiving task is obliged to close all of them appropriately. ++ ++The caller is obliged to call KDBUS_CMD_FREE with the returned offset when ++the memory is no longer needed. ++ ++ ++7.5 Canceling messages synchronously waiting for replies ++-------------------------------------------------------- ++ ++When a connection sends a message with KDBUS_MSG_FLAGS_SYNC_REPLY and ++blocks while waiting for the reply, the KDBUS_CMD_MSG_CANCEL ioctl can be ++used on the same file descriptor to cancel the message, based on its cookie. ++If there are multiple messages with the same cookie that are all synchronously ++waiting for a reply, all of them will be canceled. Obviously, this is only ++possible in multi-threaded applications. ++ ++ ++8. Name registry ++=============================================================================== ++ ++Each bus instantiates a name registry to resolve well-known names into unique ++connection IDs for message delivery. The registry will be queried when a ++message is sent with kdbus_msg.dst_id set to KDBUS_DST_ID_NAME, or when a ++registry dump is requested. ++ ++All of the below is subject to policy rules for SEE and OWN permissions. ++ ++ ++8.1 Name validity ++----------------- ++ ++A name has to comply to the following rules to be considered valid: ++ ++ - The name has two or more elements separated by a period ('.') character ++ - All elements must contain at least one character ++ - Each element must only contain the ASCII characters "[A-Z][a-z][0-9]_" ++ and must not begin with a digit ++ - The name must contain at least one '.' (period) character ++ (and thus at least two elements) ++ - The name must not begin with a '.' (period) character ++ - The name must not exceed KDBUS_NAME_MAX_LEN (255) ++ ++ ++8.2 Acquiring a name ++-------------------- ++ ++To acquire a name, a client uses the KDBUS_CMD_NAME_ACQUIRE ioctl with the ++following data structure. ++ ++struct kdbus_cmd_name { ++ __u64 size; ++ The overall size of this struct, including the name with its 0-byte string ++ terminator. ++ ++ __u64 flags; ++ Flags to control details in the name acquisition. ++ ++ KDBUS_NAME_REPLACE_EXISTING ++ Acquiring a name that is already present usually fails, unless this flag ++ is set in the call, and KDBUS_NAME_ALLOW_REPLACEMENT or (see below) was ++ set when the current owner of the name acquired it, or if the current ++ owner is an activator connection (see below). ++ ++ KDBUS_NAME_ALLOW_REPLACEMENT ++ Allow other connections to take over this name. When this happens, the ++ former owner of the connection will be notified of the name loss. ++ ++ KDBUS_NAME_QUEUE (acquire) ++ A name that is already acquired by a connection, and which wasn't ++ requested with the KDBUS_NAME_ALLOW_REPLACEMENT flag set can not be ++ acquired again. However, a connection can put itself in a queue of ++ connections waiting for the name to be released. Once that happens, the ++ first connection in that queue becomes the new owner and is notified ++ accordingly. ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ struct kdbus_item items[0]; ++ Items to submit the name. Currently, one one item of type KDBUS_ITEM_NAME ++ is expected and allowed, and the contained string must be a valid bus name. ++}; ++ ++ ++8.3 Releasing a name ++-------------------- ++ ++A connection may release a name explicitly with the KDBUS_CMD_NAME_RELEASE ++ioctl. If the connection was an implementor of an activatable name, its ++pending messages are moved back to the activator. If there are any connections ++queued up as waiters for the name, the oldest one of them will become the new ++owner. The same happens implicitly for all names once a connection terminates. ++ ++The KDBUS_CMD_NAME_RELEASE ioctl uses the same data structure as the ++acquisition call, but with slightly different field usage. ++ ++struct kdbus_cmd_name { ++ __u64 size; ++ The overall size of this struct, including the name with its 0-byte string ++ terminator. ++ ++ __u64 flags; ++ ++ struct kdbus_item items[0]; ++ Items to submit the name. Currently, one one item of type KDBUS_ITEM_NAME ++ is expected and allowed, and the contained string must be a valid bus name. ++}; ++ ++ ++8.4 Dumping the name registry ++----------------------------- ++ ++A connection may request a complete or filtered dump of currently active bus ++names with the KDBUS_CMD_NAME_LIST ioctl, which takes a struct ++kdbus_cmd_name_list as argument. ++ ++struct kdbus_cmd_name_list { ++ __u64 flags; ++ Any combination of flags to specify which names should be dumped. ++ ++ KDBUS_NAME_LIST_UNIQUE ++ List the unique (numeric) IDs of the connection, whether it owns a name ++ or not. ++ ++ KDBUS_NAME_LIST_NAMES ++ List well-known names stored in the database which are actively owned by ++ a real connection (not an activator). ++ ++ KDBUS_NAME_LIST_ACTIVATORS ++ List names that are owned by an activator. ++ ++ KDBUS_NAME_LIST_QUEUED ++ List connections that are not yet owning a name but are waiting for it ++ to become available. ++ ++ __u64 offset; ++ When the ioctl returns successfully, the offset to the name registry dump ++ inside the connection's pool will be stored in this field. ++}; ++ ++The returned list of names is stored in a struct kdbus_name_list that in turn ++contains a dynamic number of struct kdbus_cmd_name that carry the actual ++information. The fields inside that struct kdbus_cmd_name is described next. ++ ++struct kdbus_name_info { ++ __u64 size; ++ The overall size of this struct, including the name with its 0-byte string ++ terminator. ++ ++ __u64 flags; ++ The current flags for this name. Can be any combination of ++ ++ KDBUS_NAME_ALLOW_REPLACEMENT ++ ++ KDBUS_NAME_IN_QUEUE (list) ++ When retrieving a list of currently acquired name in the registry, this ++ flag indicates whether the connection actually owns the name or is ++ currently waiting for it to become available. ++ ++ KDBUS_NAME_ACTIVATOR (list) ++ An activator connection owns a name as a placeholder for an implementor, ++ which is started on demand as soon as the first message arrives. There's ++ some more information on this topic below. In contrast to ++ KDBUS_NAME_REPLACE_EXISTING, when a name is taken over from an activator ++ connection, all the messages that have been queued in the activator ++ connection will be moved over to the new owner. The activator connection ++ will still be tracked for the name and will take control again if the ++ implementor connection terminates. ++ This flag can not be used when acquiring a name, but is implicitly set ++ through KDBUS_CMD_HELLO with KDBUS_HELLO_ACTIVATOR set in ++ kdbus_cmd_hello.conn_flags. ++ ++ __u64 owner_id; ++ The owning connection's unique ID. ++ ++ __u64 conn_flags; ++ The flags of the owning connection. ++ ++ struct kdbus_item items[0]; ++ Items containing the actual name. Currently, one one item of type ++ KDBUS_ITEM_NAME will be attached. ++}; ++ ++The returned buffer must be freed with the KDBUS_CMD_FREE ioctl when the user ++is finished with it. ++ ++ ++9. Notifications ++=============================================================================== ++ ++The kernel will notify its users of the following events. ++ ++ * When connection A is terminated while connection B is waiting for a reply ++ from it, connection B is notified with a message with an item of type ++ KDBUS_ITEM_REPLY_DEAD. ++ ++ * When connection A does not receive a reply from connection B within the ++ specified timeout window, connection A will receive a message with an item ++ of type KDBUS_ITEM_REPLY_TIMEOUT. ++ ++ * When a connection is created on or removed from a bus, messages with an ++ item of type KDBUS_ITEM_ID_ADD or KDBUS_ITEM_ID_REMOVE, respectively, are ++ sent to all bus members that match these messages through their match ++ database. ++ ++ * When a connection owns or loses a name, or a name is moved from one ++ connection to another, messages with an item of type KDBUS_ITEM_NAME_ADD, ++ KDBUS_ITEM_NAME_REMOVE or KDBUS_ITEM_NAME_CHANGE are sent to all bus ++ members that match these messages through their match database. ++ ++A kernel notification is a regular kdbus message with the following details. ++ ++ * kdbus_msg.src_id == KDBUS_SRC_ID_KERNEL ++ * kdbus_msg.dst_id == KDBUS_DST_ID_BROADCAST ++ * kdbus_msg.payload_type == KDBUS_PAYLOAD_KERNEL ++ * Has exactly one of the aforementioned items attached ++ ++ ++10. Message Matching, Bloom filters ++=============================================================================== ++ ++10.1 Matches for broadcast messages from other connections ++---------------------------------------------------------- ++ ++A message addressed at the connection ID KDBUS_DST_ID_BROADCAST (~0ULL) is a ++broadcast message, delivered to all connected peers which installed a rule to ++match certain properties of the message. Without any rules installed in the ++connection, no broadcast message or kernel-side notifications will be delivered ++to the connection. Broadcast messages are subject to policy rules and TALK ++access checks. ++ ++See section 11 for details on policies, and section 11.5 for more ++details on implicit policies. ++ ++Matches for messages from other connections (not kernel notifications) are ++implemented as bloom filters. The sender adds certain properties of the message ++as elements to a bloom filter bit field, and sends that along with the ++broadcast message. ++ ++The connection adds the message properties it is interested as elements to a ++bloom mask bit field, and uploads the mask to the match rules of the ++connection. ++ ++The kernel will match the broadcast message's bloom filter against the ++connections bloom mask (simply by &-ing it), and decide whether the message ++should be delivered to the connection. ++ ++The kernel has no notion of any specific properties of the message, all it ++sees are the bit fields of the bloom filter and mask to match against. The ++use of bloom filters allows simple and efficient matching, without exposing ++any message properties or internals to the kernel side. Clients need to deal ++with the fact that they might receive broadcasts which they did not subscribe ++to, as the bloom filter might allow false-positives to pass the filter. ++ ++To allow the future extension of the set of elements in the bloom filter, the ++filter specifies a "generation" number. A later generation must always contain ++all elements of the set of the previous generation, but can add new elements ++to the set. The match rules mask can carry an array with all previous ++generations of masks individually stored. When the filter and mask are matched ++by the kernel, the mask with the closest matching "generation" is selected ++as the index into the mask array. ++ ++ ++10.2 Matches for kernel notifications ++------------------------------------ ++ ++To receive kernel generated notifications (see section 9), a connection must ++install special match rules that are different from the bloom filter matches ++described in the section above. They can be filtered by a sender connection's ++ID, by one of the name the sender connection owns at the time of sending the ++message, or by type of the notification (id/name add/remove/change). ++ ++10.3 Adding a match ++------------------- ++ ++To add a match, the KDBUS_CMD_MATCH_ADD ioctl is used, which takes a struct ++of the struct described below. ++ ++Note that each of the items attached to this command will internally create ++one match 'rule', and the collection of them, which is submitted as one block ++via the ioctl is called a 'match'. To allow a message to pass, all rules of a ++match have to be satisfied. Hence, adding more items to the command will only ++narrow the possibility of a match to effectively let the message pass, and will ++cause the connection's user space process to wake up less likely. ++ ++Multiple matches can be installed per connection. As long as one of it has a ++set of rules which allows the message to pass, this one will be decisive. ++ ++struct kdbus_cmd_match { ++ __u64 size; ++ The overall size of the struct, including its items. ++ ++ __u64 cookie; ++ A cookie which identifies the match, so it can be referred to at removal ++ time. ++ ++ __u64 flags; ++ Flags to control the behavior of the ioctl. ++ ++ KDBUS_MATCH_REPLACE: ++ Remove all entries with the given cookie before installing the new one. ++ This allows for race-free replacement of matches. ++ ++ struct kdbus_item items[0]; ++ Items to define the actual rules of the matches. The following item types ++ are expected. Each item will cause one new match rule to be created. ++ ++ KDBUS_ITEM_BLOOM_MASK ++ An item that carries the bloom filter mask to match against in its ++ data field. The payload size must match the bloom filter size that ++ was specified when the bus was created. ++ See section 10.4 for more information. ++ ++ KDBUS_ITEM_NAME ++ Specify a name that a sending connection must own at a time of sending ++ a broadcast message in order to match this rule. ++ ++ KDBUS_ITEM_ID ++ Specify a sender connection's ID that will match this rule. ++ ++ KDBUS_ITEM_NAME_ADD ++ KDBUS_ITEM_NAME_REMOVE ++ KDBUS_ITEM_NAME_CHANGE ++ These items request delivery of broadcast messages that describe a name ++ acquisition, loss, or change. The details are stored in the item's ++ kdbus_notify_name_change member. All information specified must be ++ matched in order to make the message pass. Use KDBUS_MATCH_ID_ANY to ++ match against any unique connection ID. ++ ++ KDBUS_ITEM_ID_ADD ++ KDBUS_ITEM_ID_REMOVE ++ These items request delivery of broadcast messages that are generated ++ when a connection is created or terminated. struct kdbus_notify_id_change ++ is used to store the actual match information. This item can be used to ++ monitor one particular connection ID, or, when the id field is set to ++ KDBUS_MATCH_ID_ANY, all of them. ++ ++ Other item types are ignored. ++}; ++ ++ ++10.4 Bloom filters ++------------------ ++ ++Bloom filters allow checking whether a given word is present in a dictionary. ++This allows connections to set up a mask for information it is interested in, ++and will be delivered broadcast messages that have a matching filter. ++ ++For general information on bloom filters, see ++ ++ https://en.wikipedia.org/wiki/Bloom_filter ++ ++The size of the bloom filter is defined per bus when it is created, in ++kdbus_bloom_parameter.size. All bloom filters attached to broadcast messages ++on the bus must match this size, and all bloom filter matches uploaded by ++connections must also match the size, or a multiple thereof (see below). ++ ++The calculation of the mask has to be done on the userspace side. The kernel ++just checks the bitmasks to decide whether or not to let the message pass. All ++bits in the mask must match the filter in and bit-wise AND logic, but the ++mask may have more bits set than the filter. Consequently, false positive ++matches are expected to happen, and userspace must deal with that fact. ++ ++Masks are entities that are always passed to the kernel as part of a match ++(with an item of type KDBUS_ITEM_BLOOM_MASK), and filters can be attached to ++broadcast messages (with an item of type KDBUS_ITEM_BLOOM_FILTER). ++ ++For a broadcast to match, all set bits in the filter have to be set in the ++installed match mask as well. For example, consider a bus has a bloom size ++of 8 bytes, and the following mask/filter combinations: ++ ++ filter 0x0101010101010101 ++ mask 0x0101010101010101 ++ -> matches ++ ++ filter 0x0303030303030303 ++ mask 0x0101010101010101 ++ -> doesn't match ++ ++ filter 0x0101010101010101 ++ mask 0x0303030303030303 ++ -> matches ++ ++Hence, in order to catch all messages, a mask filled with 0xff bytes can be ++installed as a wildcard match rule. ++ ++Uploaded matches may contain multiple masks, each of which in the size of the ++bloom size defined by the bus. Each block of a mask is called a 'generation', ++starting at index 0. ++ ++At match time, when a broadcast message is about to be delivered, a bloom ++mask generation is passed, which denotes which of the bloom masks the filter ++should be matched against. This allows userspace to provide backward compatible ++masks at upload time, while older clients can still match against older ++versions of filters. ++ ++ ++10.5 Removing a match ++-------------------- ++ ++Matches can be removed through the KDBUS_CMD_MATCH_REMOVE ioctl, which again ++takes struct kdbus_cmd_match as argument, but its fields are used slightly ++differently. ++ ++struct kdbus_cmd_match { ++ __u64 size; ++ The overall size of the struct. As it has no items in this use case, the ++ value should yield 16. ++ ++ __u64 cookie; ++ The cookie of the match, as it was passed when the match was added. ++ All matches that have this cookie will be removed. ++ ++ __u64 flags; ++ Unused for this use case, ++ ++ __u64 kernel_flags; ++ Valid flags for this command, returned by the kernel upon each call. ++ ++ struct kdbus_item items[0]; ++ Unused for this use case. ++}; ++ ++ ++11. Policy ++=============================================================================== ++ ++A policy databases restrict the possibilities of connections to own, see and ++talk to well-known names. It can be associated with a bus (through a policy ++holder connection) or a custom endpoint. ++ ++See section 8.1 for more details on the validity of well-known names. ++ ++Default endpoints of buses always have a policy database. The default ++policy is to deny all operations except for operations that are covered by ++implicit policies. Custom endpoints always have a policy, and by default, ++a policy database is empty. Therefore, unless policy rules are added, all ++operations will also be denied by default. ++ ++See section 11.5 for more details on implicit policies. ++ ++A set of policy rules is described by a name and multiple access rules, defined ++by the following struct. ++ ++struct kdbus_policy_access { ++ __u64 type; /* USER, GROUP, WORLD */ ++ One of the following. ++ ++ KDBUS_POLICY_ACCESS_USER ++ Grant access to a user with the uid stored in the 'id' field. ++ ++ KDBUS_POLICY_ACCESS_GROUP ++ Grant access to a user with the gid stored in the 'id' field. ++ ++ KDBUS_POLICY_ACCESS_WORLD ++ Grant access to everyone. The 'id' field is ignored. ++ ++ __u64 access; /* OWN, TALK, SEE */ ++ The access to grant. ++ ++ KDBUS_POLICY_SEE ++ Allow the name to be seen. ++ ++ KDBUS_POLICY_TALK ++ Allow the name to be talked to. ++ ++ KDBUS_POLICY_OWN ++ Allow the name to be owned. ++ ++ __u64 id; ++ For KDBUS_POLICY_ACCESS_USER, stores the uid. ++ For KDBUS_POLICY_ACCESS_GROUP, stores the gid. ++}; ++ ++Policies are set through KDBUS_CMD_HELLO (when creating a policy holder ++connection), KDBUS_CMD_CONN_UPDATE (when updating a policy holder connection), ++KDBUS_CMD_ENDPOINT_MAKE (creating a custom endpoint) or ++KDBUS_CMD_ENDPOINT_UPDATE (updating a custom endpoint). In all cases, the name ++and policy access information is stored in items of type KDBUS_ITEM_NAME and ++KDBUS_ITEM_POLICY_ACCESS. For this transport, the following rules apply. ++ ++ * An item of type KDBUS_ITEM_NAME must be followed by at least one ++ KDBUS_ITEM_POLICY_ACCESS item ++ * An item of type KDBUS_ITEM_NAME can be followed by an arbitrary number of ++ KDBUS_ITEM_POLICY_ACCESS items ++ * An arbitrary number of groups of names and access levels can be passed ++ ++uids and gids are internally always stored in the kernel's view of global ids, ++and are translated back and forth on the ioctl level accordingly. ++ ++ ++11.2 Wildcard names ++------------------- ++ ++Policy holder connections may upload names that contain the wildcard suffix ++(".*"). That way, a policy can be uploaded that is effective for every ++well-kwown name that extends the provided name by exactly one more level. ++ ++For example, if an item of a set up uploaded policy rules contains the name ++"foo.bar.*", both "foo.bar.baz" and "foo.bar.bazbaz" are valid, but ++"foo.bar.baz.baz" is not. ++ ++This allows connections to take control over multiple names that the policy ++holder doesn't need to know about when uploading the policy. ++ ++Such wildcard entries are not allowed for custom endpoints. ++ ++ ++11.3 Policy example ++------------------- ++ ++For example, a set of policy rules may look like this: ++ ++ KDBUS_ITEM_NAME: str='org.foo.bar' ++ KDBUS_ITEM_POLICY_ACCESS: type=USER, access=OWN, id=1000 ++ KDBUS_ITEM_POLICY_ACCESS: type=USER, access=TALK, id=1001 ++ KDBUS_ITEM_POLICY_ACCESS: type=WORLD, access=SEE ++ KDBUS_ITEM_NAME: str='org.blah.baz' ++ KDBUS_ITEM_POLICY_ACCESS: type=USER, access=OWN, id=0 ++ KDBUS_ITEM_POLICY_ACCESS: type=WORLD, access=TALK ++ ++That means that 'org.foo.bar' may only be owned by uid 1000, but every user on ++the bus is allowed to see the name. However, only uid 1001 may actually send ++a message to the connection and receive a reply from it. ++ ++The second rule allows 'org.blah.baz' to be owned by uid 0 only, but every user ++may talk to it. ++ ++ ++11.4 TALK access and multiple well-known names per connection ++------------------------------------------------------------- ++ ++Note that TALK access is checked against all names of a connection. ++For example, if a connection owns both 'org.foo.bar' and 'org.blah.baz', and ++the policy database allows 'org.blah.baz' to be talked to by WORLD, then this ++permission is also granted to 'org.foo.bar'. That might sound illogical, but ++after all, we allow messages to be directed to either the name or a well-known ++name, and policy is applied to the connection, not the name. In other words, ++the effective TALK policy for a connection is the most permissive of all names ++the connection owns. ++ ++If a policy database exists for a bus (because a policy holder created one on ++demand) or for a custom endpoint (which always has one), each one is consulted ++during name registry listing, name owning or message delivery. If either one ++fails, the operation is failed with -EPERM. ++ ++For best practices, connections that own names with a restricted TALK ++access should not install matches. This avoids cases where the sent ++message may pass the bloom filter due to false-positives and may also ++satisfy the policy rules. ++ ++11.5 Implicit policies ++---------------------- ++ ++Depending on the type of the endpoint, a set of implicit rules might be ++enforced. On default endpoints, the following set is enforced: ++ ++ * Privileged connections always override any installed policy. Those ++ connections could easily install their own policies, so there is no ++ reason to enforce installed policies. ++ * Connections can always talk to connections of the same user. This ++ includes broadcast messages. ++ * Connections that own names might send broadcast messages to other ++ connections that belong to a different user, but only if that ++ destination connection does not own any name. ++ ++Custom endpoints have stricter policies. The following rules apply: ++ ++ * Policy rules are always enforced, even if the connection is a privileged ++ connection. ++ * Policy rules are always enforced for TALK access, even if both ends are ++ running under the same user. This includes broadcast messages. ++ * To restrict the set of names that can be seen, endpoint policies can ++ install "SEE" policies. ++ ++ ++12. Pool ++=============================================================================== ++ ++A pool for data received from the kernel is installed for every connection of ++the bus, and is sized according to kdbus_cmd_hello.pool_size. It is accessed ++when one of the following ioctls is issued: ++ ++ * KDBUS_CMD_MSG_RECV, to receive a message ++ * KDBUS_CMD_NAME_LIST, to dump the name registry ++ * KDBUS_CMD_CONN_INFO, to retrieve information on a connection ++ ++Internally, the pool is organized in slices, stored in an rb-tree. The offsets ++returned by either one of the aforementioned ioctls describe offsets inside the ++pool. In order to make the slice available for subsequent calls, KDBUS_CMD_FREE ++has to be called on the offset. ++ ++To access the memory, the caller is expected to mmap() it to its task, like ++this: ++ ++ /* ++ * POOL_SIZE has to be a multiple of PAGE_SIZE, and it must match the ++ * value that was previously passed in the .pool_size field of struct ++ * kdbus_cmd_hello. ++ */ ++ ++ buf = mmap(NULL, POOL_SIZE, PROT_READ, MAP_PRIVATE, conn_fd, 0); ++ ++ ++13. Metadata ++=============================================================================== ++ ++When a message is delivered to a receiver connection, it is augmented by ++metadata items in accordance to the destination's current attach flags. The ++information stored in those metadata items refer to the sender task at the ++time of sending the message, so even if any detail of the sender task has ++already changed upon message reception (or if the sender task does not exist ++anymore), the information is still preserved and won't be modfied until the ++message is freed. ++ ++Note that there are two exceptions to the above rules: ++ ++ a) Kernel generated messages don't have a source connection, so they won't be ++ augmented. ++ ++ b) If a connection was created with faked credentials (see section 6.2), ++ the only attached metadata items are the ones provided by the connection ++ itself. The destination's attach_flags won't be looked at in such cases. ++ ++Also, there are two things to be considered by userspace programs regarding ++those metadata items: ++ ++ a) Userspace must cope with the fact that it might get more metadata than ++ they requested. That happens, for example, when a broadcast message is ++ sent and receivers have different attach flags. Items that haven't been ++ requested should hence be silently ignored. ++ ++ b) Userspace might not always get all requested metadata items that it ++ requested. That is because some of those items are only added if a ++ corresponding kernel feature has been enabled. Also, the two exceptions ++ described above will as well lead to less items be attached than ++ requested. ++ ++ ++13.1 Known item types ++--------------------- ++ ++The following attach flags are currently supported. ++ ++ KDBUS_ATTACH_TIMESTAMP ++ Attaches an item of type KDBUS_ITEM_TIMESTAMP which contains both the ++ monotonic and the realtime timestamp, taken when the message was ++ processed on the kernel side. ++ ++ KDBUS_ATTACH_CREDS ++ Attaches an item of type KDBUS_ITEM_CREDS, containing credentials as ++ described in kdbus_creds: the uid, gid, pid, tid and starttime of the task. ++ ++ KDBUS_ATTACH_AUXGROUPS ++ Attaches an item of type KDBUS_ITEM_AUXGROUPS, containing a dynamic ++ number of auxiliary groups the sending task was a member of. ++ ++ KDBUS_ATTACH_NAMES ++ Attaches items of type KDBUS_ITEM_NAME, one for each name the sending ++ connection currently owns. The name is stored in kdbus_item.str for each ++ of them. ++ ++ KDBUS_ATTACH_COMM ++ Attaches an items of type KDBUS_ITEM_PID_COMM and KDBUS_ITEM_TID_COMM, ++ both transporting the sending task's 'comm', for both the pid and the tid. ++ The strings are stored in kdbus_item.str. ++ ++ KDBUS_ATTACH_EXE ++ Attaches an item of type KDBUS_ITEM_EXE, containing the path to the ++ executable of the sending task, stored in kdbus_item.str. ++ ++ KDBUS_ATTACH_CMDLINE ++ Attaches an item of type KDBUS_ITEM_CMDLINE, containing the command line ++ arguments of the sending task, as an array of strings, stored in ++ kdbus_item.str. ++ ++ KDBUS_ATTACH_CGROUP ++ Attaches an item of type KDBUS_ITEM_CGROUP with the task's cgroup path. ++ ++ KDBUS_ATTACH_CAPS ++ Attaches an item of type KDBUS_ITEM_CAPS, carrying sets of capabilities ++ that should be accessed via kdbus_item.caps.caps. Also, userspace should ++ be written in a way that it takes kdbus_item.caps.last_cap into account, ++ and derive the number of sets and rows from the item size and the reported ++ number of valid capability bits. ++ ++ KDBUS_ATTACH_SECLABEL ++ Attaches an item of type KDBUS_ITEM_SECLABEL, which contains the SELinux ++ security label of the sending task. Access via kdbus_item->str. ++ ++ KDBUS_ATTACH_AUDIT ++ Attaches an item of type KDBUS_ITEM_AUDIT, which contains the audio label ++ of the sending taskj. Access via kdbus_item->str. ++ ++ KDBUS_ATTACH_CONN_NAME ++ Attaches an item of type KDBUS_ITEM_CONN_NAME that contain's the ++ sending's connection current name in kdbus_item.str. ++ ++ ++13.1 Metadata and namespaces ++---------------------------- ++Note that if the user or PID namespaces of a connection at the time of sending ++differ from those that were active then the connection was created ++(KDBUS_CMD_HELLO), data structures such as messages will not have any metadata ++attached to prevent leaking security-relevant information. ++ ++ ++14. Error codes ++=============================================================================== ++ ++Below is a list of error codes that might be returned by the individual ++ioctl commands. The list focuses on the return values from kdbus code itself, ++and might not cover those of all kernel internal functions. ++ ++For all ioctls: ++ ++ -ENOMEM The kernel memory is exhausted ++ -ENOTTY Illegal ioctl command issued for the file descriptor ++ -ENOSYS The requested functionality is not available ++ ++For all ioctls that carry a struct as payload: ++ ++ -EFAULT The supplied data pointer was not 64-bit aligned, or was ++ inaccessible from the kernel side. ++ -EINVAL The size inside the supplied struct was smaller than expected ++ -EMSGSIZE The size inside the supplied struct was bigger than expected ++ -ENAMETOOLONG A supplied name is larger than the allowed maximum size ++ ++For KDBUS_CMD_BUS_MAKE: ++ ++ -EINVAL The flags supplied in the kdbus_cmd_make struct are invalid or ++ the supplied name does not start with the current uid and a '-' ++ -EEXIST A bus of that name already exists ++ -ESHUTDOWN The domain for the bus is already shut down ++ -EMFILE The maximum number of buses for the current user is exhausted ++ ++For KDBUS_CMD_DOMAIN_MAKE: ++ ++ -EPERM The calling user does not have CAP_IPC_OWNER set, or ++ -EINVAL The flags supplied in the kdbus_cmd_make struct are invalid, or ++ no name supplied for top-level domain ++ -EEXIST A domain of that name already exists ++ ++For KDBUS_CMD_ENDPOINT_MAKE: ++ ++ -EPERM The calling user is not privileged (see Terminology) ++ -EINVAL The flags supplied in the kdbus_cmd_make struct are invalid ++ -EEXIST An endpoint of that name already exists ++ ++For KDBUS_CMD_HELLO: ++ ++ -EFAULT The supplied pool size was 0 or not a multiple of the page size ++ -EINVAL The flags supplied in the kdbus_cmd_make struct are invalid, or ++ an illegal combination of KDBUS_HELLO_MONITOR, ++ KDBUS_HELLO_ACTIVATOR and KDBUS_HELLO_POLICY_HOLDER was passed ++ in the flags, or an invalid set of items was supplied ++ -EPERM An KDBUS_ITEM_CREDS items was supplied, but the current user is ++ not privileged ++ -ESHUTDOWN The bus has already been shut down ++ -EMFILE The maximum number of connection on the bus has been reached ++ ++For KDBUS_CMD_BYEBYE: ++ ++ -EALREADY The connection has already been shut down ++ -EBUSY There are still messages queued up in the connection's pool ++ ++For KDBUS_CMD_MSG_SEND: ++ ++ -EOPNOTSUPP The connection is unconnected, or a fd was passed that is ++ either a kdbus handle itself or a unix domain socket. Both is ++ currently unsupported. ++ -EINVAL The submitted payload type is KDBUS_PAYLOAD_KERNEL, ++ KDBUS_MSG_FLAGS_EXPECT_REPLY was set without a timeout value, ++ KDBUS_MSG_FLAGS_SYNC_REPLY was set without ++ KDBUS_MSG_FLAGS_EXPECT_REPLY, an invalid item was supplied, ++ src_id was != 0 and different from the current connection's ID, ++ a supplied memfd had a size of 0, a string was not properly ++ nul-terminated ++ -ENOTUNIQ KDBUS_MSG_FLAGS_EXPECT_REPLY was set, but the dst_id is set ++ to KDBUS_DST_ID_BROADCAST ++ -E2BIG Too many items ++ -EMSGSIZE A payload vector was too big, and the current user is ++ unprivileged. ++ -ENOTUNIQ A fd or memfd payload was passed in a broadcast message, or ++ a timeout was given for a broadcast message ++ -EEXIST Multiple KDBUS_ITEM_FDS or KDBUS_ITEM_BLOOM_FILTER, ++ KDBUS_ITEM_DST_NAME were supplied ++ -EBADF A memfd item contained an illegal fd ++ -EMEDIUMTYPE A file descriptor which is not a kdbus memfd was ++ refused to send as KDBUS_MSG_PAYLOAD_MEMFD. ++ -EMFILE Too many file descriptors inside a KDBUS_ITEM_FDS ++ -EBADMSG An item had illegal size, both a dst_id and a ++ KDBUS_ITEM_DST_NAME was given, or both a name and a bloom ++ filter was given ++ -ETXTBSY A kdbus memfd file cannot be sealed or the seal removed, ++ because it is shared with other processes or still mmap()ed ++ -ECOMM A peer does not accept the file descriptors addressed to it ++ -EFAULT The supplied bloom filter size was not 64-bit aligned ++ -EDOM The supplied bloom filter size did not match the bloom filter ++ size of the bus ++ -EDESTADDRREQ dst_id was set to KDBUS_DST_ID_NAME, but no KDBUS_ITEM_DST_NAME ++ was attached ++ -ESRCH The name to look up was not found in the name registry ++ -EADDRNOTAVAIL KDBUS_MSG_FLAGS_NO_AUTO_START was given but the destination ++ connection is an activator. ++ -ENXIO The passed numeric destination connection ID couldn't be found, ++ or is not connected ++ -ECONNRESET The destination connection is no longer active ++ -ETIMEDOUT Timeout while synchronously waiting for a reply ++ -EINTR System call interrupted while synchronously waiting for a reply ++ -EPIPE When sending a message, a synchronous reply from the receiving ++ connection was expected but the connection died before ++ answering ++ -ECANCELED A synchronous message sending was cancelled ++ -ENOBUFS Too many pending messages on the receiver side ++ -EREMCHG Both a well-known name and a unique name (ID) was given, but ++ the name is not currently owned by that connection. ++ ++For KDBUS_CMD_MSG_RECV: ++ ++ -EINVAL Invalid flags or offset ++ -EAGAIN No message found in the queue ++ -ENOMSG No message of the requested priority found ++ ++For KDBUS_CMD_MSG_CANCEL: ++ ++ -EINVAL Invalid flags ++ -ENOENT Pending message with the supplied cookie not found ++ ++For KDBUS_CMD_FREE: ++ ++ -ENXIO No pool slice found at given offset ++ -EINVAL Invalid flags provided, the offset is valid, but the user is ++ not allowed to free the slice. This happens, for example, if ++ the offset was retrieved with KDBUS_RECV_PEEK. ++ ++For KDBUS_CMD_NAME_ACQUIRE: ++ ++ -EINVAL Illegal command flags, illegal name provided, or an activator ++ tried to acquire a second name ++ -EPERM Policy prohibited name ownership ++ -EALREADY Connection already owns that name ++ -EEXIST The name already exists and can not be taken over ++ -ECONNRESET The connection was reset during the call ++ ++For KDBUS_CMD_NAME_RELEASE: ++ ++ -EINVAL Invalid command flags, or invalid name provided ++ -ESRCH Name is not found found in the registry ++ -EADDRINUSE Name is owned by a different connection and can't be released ++ ++For KDBUS_CMD_NAME_LIST: ++ ++ -EINVAL Invalid flags ++ -ENOBUFS No available memory in the connection's pool. ++ ++For KDBUS_CMD_CONN_INFO: ++ ++ -EINVAL Invalid flags, or neither an ID nor a name was provided, ++ or the name is invalid. ++ -ESRCH Connection lookup by name failed ++ -ENXIO No connection with the provided number connection ID found ++ ++For KDBUS_CMD_CONN_UPDATE: ++ ++ -EINVAL Illegal flags or items ++ -EOPNOTSUPP Operation not supported by connection. ++ -E2BIG Too many policy items attached ++ -EINVAL Wildcards submitted in policy entries, or illegal sequence ++ of policy items ++ ++For KDBUS_CMD_ENDPOINT_UPDATE: ++ ++ -E2BIG Too many policy items attached ++ -EINVAL Invalid flags, or wildcards submitted in policy entries, ++ or illegal sequence of policy items ++ ++For KDBUS_CMD_MATCH_ADD: ++ ++ -EINVAL Illegal flags or items ++ -EDOM Illegal bloom filter size ++ -EMFILE Too many matches for this connection ++ ++For KDBUS_CMD_MATCH_REMOVE: ++ ++ -EINVAL Illegal flags ++ -ENOENT A match entry with the given cookie could not be found. |