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: Sheng Yong <[email protected]>
Signed-off-by: Wang Shuai <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Gao Xiang: minor update on documentation and the error message. ]
Reviewed-by: Hongbo Li <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>

0 files changed, 0 insertions, 0 deletions