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| author | Gao Xiang <hsiangkao@linux.alibaba.com> | 2026-06-22 03:44:14 +0800 |
|---|---|---|
| committer | Gao Xiang <hsiangkao@linux.alibaba.com> | 2026-06-22 06:48:59 +0800 |
| commit | e87827da8c351db0de504534e6aa17be3014bc25 (patch) | |
| tree | aaf2caba31c00e8f5663d837d0ccb48d57537107 /fs | |
| parent | 28c5d230980bdd8cb18c073225296c7747995935 (diff) | |
| download | ath-e87827da8c351db0de504534e6aa17be3014bc25.tar.gz | |
erofs: add sparse support to pcluster layout
Although zeros can be compressed transparently on EROFS using fixed-size
output compression so that it is never prioritized in the Android use
cases, indicating entire pclusters as holes is still useful to preserve
holes in the sparse datasets; otherwise overlayfs will allocate more
space when copying up, and SEEK_HOLE won't report any hole.
This patch introduces two ways to mark a pcluster as a hole:
- A new Z_EROFS_LI_HOLE compatible flag (bit 14) in the HEAD lcluster
advise field for non-compact (full) indexes;
- A 0-block CBLKCNT value on the first NONHEAD lcluster.
The hole tag is preferred for maximum compatibility since pre-existing
kernels that do not understand Z_EROFS_LI_HOLE will decompress at the
stored blkaddr (the same blkaddr will be shared among all sparse
pclusters). Only the 0-block CBLKCNT approach also works for compact
indexes, but it is limited to big pclusters and new kernels.
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/erofs/erofs_fs.h | 2 | ||||
| -rw-r--r-- | fs/erofs/zmap.c | 33 |
2 files changed, 24 insertions, 11 deletions
diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h index 7871b16c1d333..16ec4fd33ac67 100644 --- a/fs/erofs/erofs_fs.h +++ b/fs/erofs/erofs_fs.h @@ -396,6 +396,8 @@ enum { /* (noncompact only, HEAD) This pcluster refers to partial decompressed data */ #define Z_EROFS_LI_PARTIAL_REF (1 << 15) +/* (noncompact only, HEAD) This pcluster can also be regarded as a HOLE */ +#define Z_EROFS_LI_HOLE (1 << 14) /* Set on 1st non-head lcluster to store compressed block counti (in blocks) */ #define Z_EROFS_LI_D0_CBLKCNT (1 << 11) diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c index e1a02a2c8406b..bab5216135524 100644 --- a/fs/erofs/zmap.c +++ b/fs/erofs/zmap.c @@ -15,8 +15,9 @@ struct z_erofs_maprecorder { u8 type, headtype; u16 clusterofs; u16 delta[2]; - erofs_blk_t pblk, compressedblks; + erofs_blk_t pblk; erofs_off_t nextpackoff; + int compressedblks; bool partialref, in_mbox; }; @@ -54,7 +55,12 @@ static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m, u64 lcn) } else { m->partialref = !!(advise & Z_EROFS_LI_PARTIAL_REF); m->clusterofs = le16_to_cpu(di->di_clusterofs); - m->pblk = le32_to_cpu(di->di_u.blkaddr); + if (advise & Z_EROFS_LI_HOLE) { + m->compressedblks = 0; + m->pblk = EROFS_NULL_ADDR; + } else { + m->pblk = le32_to_cpu(di->di_u.blkaddr); + } } return 0; } @@ -309,9 +315,10 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m, ((m->headtype == Z_EROFS_LCLUSTER_TYPE_PLAIN || m->headtype == Z_EROFS_LCLUSTER_TYPE_HEAD2) && !bigpcl2) || (lcn << vi->z_lclusterbits) >= inode->i_size) - m->compressedblks = 1; + if (m->compressedblks < 0) + m->compressedblks = 1; - if (m->compressedblks) + if (m->compressedblks >= 0) goto out; err = z_erofs_load_lcluster_from_disk(m, lcn, false); @@ -329,19 +336,22 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m, DBG_BUGON(lcn == initial_lcn && m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD); - if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD && m->delta[0] != 1) { + if (m->type != Z_EROFS_LCLUSTER_TYPE_NONHEAD) { + /* + * if the 1st NONHEAD lcluster is actually PLAIN or HEAD type + * rather than CBLKCNT, it's a 1 block-sized pcluster. + */ + if (m->compressedblks < 0) + m->compressedblks = 1; + } else if (m->delta[0] != 1 || m->compressedblks < 0) { erofs_err(sb, "bogus CBLKCNT @ lcn %llu of nid %llu", lcn, vi->nid); DBG_BUGON(1); return -EFSCORRUPTED; } - /* - * if the 1st NONHEAD lcluster is actually PLAIN or HEAD type rather - * than CBLKCNT, it's a 1 block-sized pcluster. - */ - if (m->type != Z_EROFS_LCLUSTER_TYPE_NONHEAD || !m->compressedblks) - m->compressedblks = 1; out: + if (!m->compressedblks) + m->map->m_flags &= ~EROFS_MAP_MAPPED; m->map->m_plen = erofs_pos(sb, m->compressedblks); return 0; } @@ -395,6 +405,7 @@ static int z_erofs_map_blocks_fo(struct inode *inode, .inode = inode, .map = map, .in_mbox = erofs_inode_in_metabox(inode), + .compressedblks = -1, }; unsigned int endoff; unsigned long initial_lcn; |