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BACKPORT: erofs: add 'fsoffset' mount option to specify filesystem offset

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When attempting to use an archive file, such as APEX on android,
as a file-backed mount source, it fails because EROFS image within
the archive file does not start at offset 0. As a result, a loop
or a dm device is still needed to attach the image file at an
appropriate offset first. Similarly, if an EROFS image within a
block device does not start at offset 0, it cannot be mounted
directly either.

To address this issue, this patch adds a new mount option `fsoffset=x'
to accept a start offset for the primary device. The offset should be
aligned to the block size. EROFS will add this offset before performing
read requests.

Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
Signed-off-by: Wang Shuai <wangshuai12@xiaomi.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250517090544.2687651-1-shengyong1@xiaomi.com
[ Gao Xiang: minor update on documentation and the error message. ]
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Bug: 428292438
Change-Id: Iae548d62c473aa380f394ecca1422588c25ef418
(cherry picked from commit c36ec00d7f67590cb03e233959cd92fe969753a3)
[Wang Shuai: Resolved minor conflict in fs/erofs/super.c ]
Signed-off-by: Wang Shuai <wangshuai12@xiaomi.corp-partner.google.com>
This commit is contained in:
Sheng Yong
2025-05-17 17:05:43 +08:00
committed by Sandeep Dhavale
parent 399deda7b5
commit 4d0200d0a9
6 changed files with 25 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
Documentation/filesystems/erofs.rst
View File

@@ -128,6 +128,7 @@ device=%s Specify a path to an extra device to be used together.
fsid=%s Specify a filesystem image ID for Fscache back-end.
domain_id=%s Specify a domain ID in fscache mode so that different images
with the same blobs under a given domain ID can share storage.
fsoffset=%llu Specify block-aligned filesystem offset for the primary device.
=================== =========================================================
Sysfs Entries

5
fs/erofs/data.c
View File

@@ -28,7 +28,7 @@ void erofs_put_metabuf(struct erofs_buf *buf)
void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset,
enum erofs_kmap_type type)
{
pgoff_t index = offset >> PAGE_SHIFT;
pgoff_t index = (buf->off + offset) >> PAGE_SHIFT;
struct folio *folio = NULL;
if (buf->page) {
@@ -62,6 +62,7 @@ void erofs_init_metabuf(struct erofs_buf *buf, struct super_block *sb)
struct erofs_sb_info *sbi = EROFS_SB(sb);
buf->file = NULL;
buf->off = sbi->dif0.fsoff;
if (erofs_is_fileio_mode(sbi)) {
buf->file = sbi->dif0.file; /* some fs like FUSE needs it */
buf->mapping = buf->file->f_mapping;
@@ -326,7 +327,7 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
iomap->private = buf.base;
} else {
iomap->type = IOMAP_MAPPED;
iomap->addr = mdev.m_pa;
iomap->addr = mdev.m_dif->fsoff + mdev.m_pa;
if (flags & IOMAP_DAX)
iomap->addr += mdev.m_dif->dax_part_off;
}

3
fs/erofs/fileio.c
View File

@@ -147,7 +147,8 @@ io_retry:
if (err)
break;
io->rq = erofs_fileio_rq_alloc(&io->dev);
io->rq->bio.bi_iter.bi_sector = io->dev.m_pa >> 9;
io->rq->bio.bi_iter.bi_sector =
(io->dev.m_dif->fsoff + io->dev.m_pa) >> 9;
attached = 0;
}
if (!bio_add_folio(&io->rq->bio, folio, len, cur))

3
fs/erofs/internal.h
View File

@@ -51,7 +51,7 @@ struct erofs_device_info {
struct erofs_fscache *fscache;
struct file *file;
struct dax_device *dax_dev;
u64 dax_part_off;
u64 fsoff, dax_part_off;
u32 blocks;
u32 mapped_blkaddr;
@@ -213,6 +213,7 @@ enum erofs_kmap_type {
struct erofs_buf {
struct address_space *mapping;
struct file *file;
u64 off;
struct page *page;
void *base;
enum erofs_kmap_type kmap_type;

16
fs/erofs/super.c
View File

@@ -380,7 +380,7 @@ static void erofs_default_options(struct erofs_sb_info *sbi)
enum {
Opt_user_xattr, Opt_acl, Opt_cache_strategy, Opt_dax, Opt_dax_enum,
Opt_device, Opt_fsid, Opt_domain_id, Opt_directio,
Opt_device, Opt_fsid, Opt_domain_id, Opt_directio, Opt_fsoffset,
Opt_err
};
@@ -408,6 +408,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
fsparam_string("fsid", Opt_fsid),
fsparam_string("domain_id", Opt_domain_id),
fsparam_flag_no("directio", Opt_directio),
fsparam_u64("fsoffset", Opt_fsoffset),
{}
};
@@ -531,6 +532,9 @@ static int erofs_fc_parse_param(struct fs_context *fc,
errorfc(fc, "%s option not supported", erofs_fs_parameters[opt].name);
#endif
break;
case Opt_fsoffset:
sbi->dif0.fsoff = result.uint_64;
break;
default:
return -ENOPARAM;
}
@@ -645,6 +649,14 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
}
}
if (sbi->dif0.fsoff) {
if (sbi->dif0.fsoff & (sb->s_blocksize - 1))
return invalfc(fc, "fsoffset %llu is not aligned to block size %lu",
sbi->dif0.fsoff, sb->s_blocksize);
if (erofs_is_fscache_mode(sb))
return invalfc(fc, "cannot use fsoffset in fscache mode");
}
if (test_opt(&sbi->opt, DAX_ALWAYS)) {
if (!sbi->dif0.dax_dev) {
errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
@@ -976,6 +988,8 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
if (sbi->domain_id)
seq_printf(seq, ",domain_id=%s", sbi->domain_id);
#endif
if (sbi->dif0.fsoff)
seq_printf(seq, ",fsoffset=%llu", sbi->dif0.fsoff);
return 0;
}

3
fs/erofs/zdata.c
View File

@@ -1773,7 +1773,8 @@ drain_io:
bio = bio_alloc(mdev.m_bdev, BIO_MAX_VECS,
REQ_OP_READ, GFP_NOIO);
bio->bi_end_io = z_erofs_endio;
bio->bi_iter.bi_sector = cur >> 9;
bio->bi_iter.bi_sector =
(mdev.m_dif->fsoff + cur) >> 9;
bio->bi_private = q[JQ_SUBMIT];
if (readahead)
bio->bi_opf |= REQ_RAHEAD;