[PATCH v4 2/2] erofs: add 'fsoffset' mount option for file-backed & bdev-based mounts
Hongbo Li
lihongbo22 at huawei.com
Tue May 13 17:06:18 AEST 2025
On 2025/4/8 20:23, Sheng Yong wrote:
> From: Sheng Yong <shengyong1 at 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 `fsoffset=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
Hi Yong,
Why the offset should be aligned to block size? I mean, we can use the
original offset directly during read, and then add this offset after
reading.
Thanks,
Hongbo
> before performing read requests.
>
> Signed-off-by: Sheng Yong <shengyong1 at xiaomi.com>
> Signed-off-by: Wang Shuai <wangshuai12 at 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(-)
> ---
> v4: * change mount option `offset=x' to `fsoffset=x'
>
> v3: * rename `offs' to `off'
> * parse offset using fsparam_u64 and validate it in fill_super
> * update bi_sector inline
> https://lore.kernel.org/linux-erofs/98585dd8-d0b6-4000-b46d-a08c64eae44d@linux.alibaba.com
>
> 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-42a8-9557-4713e7e35153@linux.alibaba.com
>
> v1: https://lore.kernel.org/all/20250324022849.2715578-1-shengyong1@xiaomi.com/
>
> diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
> index c293f8e37468..0fa4c7826203 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.
> +fsoffset=%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..e96fea9f2d18 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_fsoffset,
> 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("fsoffset", Opt_fsoffset),
> {}
> };
>
> @@ -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_fsoffset:
> + 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, "fsoffset %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, "fsoffset only supports file or bdev backing");
> + if (sbi->dif0.off + (1 << sbi->blkszbits) > devsz)
> + return invalfc(fc, "fsoffset 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, ",fsoffset=%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);
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