From: Sheng Yong <shengyo...@xiaomi.com>
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
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 `offset=x'
to accept a start offset for both file-backed and bdev-based mounts.
The offset should be aligned to block size. EROFS will add this offset
before performing read requests.
Signed-off-by: Sheng Yong <shengyo...@xiaomi.com>
Signed-off-by: Wang Shuai <wangshua...@xiaomi.com>
---
Documentation/filesystems/erofs.rst | 1 +
fs/erofs/data.c | 8 ++++++--
fs/erofs/fileio.c | 4 +++-
fs/erofs/internal.h | 2 ++
fs/erofs/super.c | 24 +++++++++++++++++++++++-
fs/erofs/zdata.c | 22 ++++++++++++++--------
6 files changed, 49 insertions(+), 12 deletions(-)
---
v3: * rename `offs' to `off'
* parse offset using fsparam_u64 and validate it in fill_super
* update bi_sector inline
v2: * add a new mount option `offset=X' for start offset, and offset
should be aligned to PAGE_SIZE
* add start offset for both file-backed and bdev-based mounts
https://lore.kernel.org/linux-erofs/0725c2ec-528c-42a8-9557-4713e7e35...@linux.alibaba.com
v1: https://lore.kernel.org/all/20250324022849.2715578-1-shengyo...@xiaomi.com/
diff --git a/Documentation/filesystems/erofs.rst
b/Documentation/filesystems/erofs.rst
index c293f8e37468..44dbfa6cffb1 100644
--- a/Documentation/filesystems/erofs.rst
+++ b/Documentation/filesystems/erofs.rst
@@ -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.
+offset=%s Specify image offset for file-backed or bdev-based
mounts.
===================
=========================================================
Sysfs Entries
diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 2409d2ab0c28..7da503480f4d 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -27,9 +27,12 @@ void erofs_put_metabuf(struct erofs_buf *buf)
void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset, bool need_kmap)
{
- pgoff_t index = offset >> PAGE_SHIFT;
+ pgoff_t index;
struct folio *folio = NULL;
+ offset += buf->off;
+ index = offset >> PAGE_SHIFT;
+
if (buf->page) {
folio = page_folio(buf->page);
if (folio_file_page(folio, index) != buf->page)
@@ -54,6 +57,7 @@ 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.off;
if (erofs_is_fileio_mode(sbi)) {
buf->file = sbi->dif0.file; /* some fs like FUSE needs it */
buf->mapping = buf->file->f_mapping;
@@ -299,7 +303,7 @@ 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 = EROFS_SB(sb)->dif0.off + mdev.m_pa;
if (flags & IOMAP_DAX)
iomap->addr += mdev.m_dif->dax_part_off;
}
diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c
index 4fa0a0121288..2c003cbb0fbb 100644
--- a/fs/erofs/fileio.c
+++ b/fs/erofs/fileio.c
@@ -52,7 +52,9 @@ static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq)
if (!rq)
return;
- rq->iocb.ki_pos = rq->bio.bi_iter.bi_sector << SECTOR_SHIFT;
+
+ rq->iocb.ki_pos = EROFS_SB(rq->sb)->dif0.off +
+ (rq->bio.bi_iter.bi_sector << SECTOR_SHIFT);
rq->iocb.ki_ioprio = get_current_ioprio();
rq->iocb.ki_complete = erofs_fileio_ki_complete;
if (test_opt(&EROFS_SB(rq->sb)->opt, DIRECT_IO) &&
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 4ac188d5d894..10656bd986bd 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -43,6 +43,7 @@ struct erofs_device_info {
char *path;
struct erofs_fscache *fscache;
struct file *file;
+ loff_t off;
struct dax_device *dax_dev;
u64 dax_part_off;
@@ -199,6 +200,7 @@ enum {
struct erofs_buf {
struct address_space *mapping;
struct file *file;
+ loff_t off;
struct page *page;
void *base;
};
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index cadec6b1b554..bd2a2c634f1d 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -356,7 +356,7 @@ 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_offset,
Opt_err
};
@@ -384,6 +384,7 @@ 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("offset", Opt_offset),
{}
};
@@ -507,6 +508,9 @@ 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_offset:
+ sbi->dif0.off = result.uint_64;
+ break;
}
return 0;
}
@@ -600,6 +604,22 @@ static int erofs_fc_fill_super(struct super_block *sb,
struct fs_context *fc)
&sbi->dif0.dax_part_off, NULL, NULL);
}
+ if (sbi->dif0.off) {
+ loff_t devsz;
+
+ if (sbi->dif0.off & ((1 << sbi->blkszbits) - 1))
+ return invalfc(fc, "offset %lld not aligned to block
size",
+ sbi->dif0.off);
+ if (sb->s_bdev)
+ devsz = bdev_nr_bytes(sb->s_bdev);
+ else if (erofs_is_fileio_mode(sbi))
+ devsz = i_size_read(file_inode(sbi->dif0.file));
+ else
+ return invalfc(fc, "offset only supports file or bdev
backing");
+ if (sbi->dif0.off + (1 << sbi->blkszbits) > devsz)
+ return invalfc(fc, "offset exceeds device size");
+ }
+
err = erofs_read_superblock(sb);
if (err)
return err;
@@ -948,6 +968,8 @@ 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.off)
+ seq_printf(seq, ",offset=%lld", sbi->dif0.off);
return 0;
}
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 0671184d9cf1..671527b63c6d 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1624,7 +1624,8 @@ static void z_erofs_submit_queue(struct z_erofs_frontend
*f,
bool *force_fg, bool readahead)
{
struct super_block *sb = f->inode->i_sb;
- struct address_space *mc = MNGD_MAPPING(EROFS_SB(sb));
+ struct erofs_sb_info *sbi = EROFS_SB(sb);
+ struct address_space *mc = MNGD_MAPPING(sbi);
struct z_erofs_pcluster **qtail[NR_JOBQUEUES];
struct z_erofs_decompressqueue *q[NR_JOBQUEUES];
struct z_erofs_pcluster *pcl, *next;
@@ -1673,12 +1674,15 @@ static void z_erofs_submit_queue(struct
z_erofs_frontend *f,
if (bio && (cur != last_pa ||
bio->bi_bdev != mdev.m_bdev)) {
drain_io:
- if (erofs_is_fileio_mode(EROFS_SB(sb)))
+ if (erofs_is_fileio_mode(sbi)) {
erofs_fileio_submit_bio(bio);
- else if (erofs_is_fscache_mode(sb))
+ } else if (erofs_is_fscache_mode(sb)) {
erofs_fscache_submit_bio(bio);
- else
+ } else {
+ bio->bi_iter.bi_sector +=
+ sbi->dif0.off >> SECTOR_SHIFT;
submit_bio(bio);
+ }
if (memstall) {
psi_memstall_leave(&pflags);
@@ -1703,7 +1707,7 @@ static void z_erofs_submit_queue(struct z_erofs_frontend
*f,
}
if (!bio) {
- if (erofs_is_fileio_mode(EROFS_SB(sb)))
+ if (erofs_is_fileio_mode(sbi))
bio = erofs_fileio_bio_alloc(&mdev);
else if (erofs_is_fscache_mode(sb))
bio = erofs_fscache_bio_alloc(&mdev);
@@ -1732,12 +1736,14 @@ static void z_erofs_submit_queue(struct
z_erofs_frontend *f,
} while (next != Z_EROFS_PCLUSTER_TAIL);
if (bio) {
- if (erofs_is_fileio_mode(EROFS_SB(sb)))
+ if (erofs_is_fileio_mode(sbi)) {
erofs_fileio_submit_bio(bio);
- else if (erofs_is_fscache_mode(sb))
+ } else if (erofs_is_fscache_mode(sb)) {
erofs_fscache_submit_bio(bio);
- else
+ } else {
+ bio->bi_iter.bi_sector += sbi->dif0.off >> SECTOR_SHIFT;
submit_bio(bio);
+ }
}
if (memstall)
psi_memstall_leave(&pflags);
--
2.43.0
