Commit c36ec00d authored by Sheng Yong's avatar Sheng Yong Committed by Gao Xiang
Browse files

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



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: default avatarSheng Yong <shengyong1@xiaomi.com>
Signed-off-by: default avatarWang Shuai <wangshuai12@xiaomi.com>
Reviewed-by: default avatarGao 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: default avatarHongbo Li <lihongbo22@huawei.com>
Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
parent 12bf25d1

Documentation/filesystems/erofs.rst

+1 −0
Original line number Diff line number Diff line
@@ -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

fs/erofs/data.c

+3 −2
Original line number Diff line number Diff line
@@ -27,7 +27,7 @@ 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 = (buf->off + offset) >> PAGE_SHIFT;

	struct folio *folio = NULL;



	if (buf->page) {
@@ -54,6 +54,7 @@ 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;
@@ -299,7 +300,7 @@ 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;

	}

fs/erofs/fileio.c

+2 −1
Original line number Diff line number Diff line
@@ -147,7 +147,8 @@ static int erofs_fileio_scan_folio(struct erofs_fileio *io, struct folio *folio) 
				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))

fs/erofs/internal.h

+2 −1
Original line number Diff line number Diff line
@@ -44,7 +44,7 @@ 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;



	erofs_blk_t blocks;

	erofs_blk_t uniaddr;
@@ -199,6 +199,7 @@ enum { 
struct erofs_buf {

	struct address_space *mapping;

	struct file *file;

	u64 off;

	struct page *page;

	void *base;

};

fs/erofs/super.c

+15 −1
Original line number Diff line number Diff line
@@ -359,7 +359,7 @@ 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,

};



static const struct constant_table erofs_param_cache_strategy[] = {
@@ -386,6 +386,7 @@ 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),

	{}

};
@@ -509,6 +510,9 @@ 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;

	}

	return 0;

}
@@ -649,6 +653,14 @@ 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.");
@@ -978,6 +990,8 @@ 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;

}