On Mon, Aug 03, 2026 at 02:01:41PM +0200, Giuseppe Scrivano wrote: > Chao Yu <[email protected]> writes: > > > On 7/29/26 00:05, Giuseppe Scrivano wrote: > >> Allow userspace to pass an already-opened file descriptor as the mount > >> source instead of a path string. This is useful for tools that already > >> hold an fd to the image, such as composefs reusing an existing erofs > >> backing file. > >> Signed-off-by: Giuseppe Scrivano <[email protected]> > >> --- > >> v4: > >> https://lore.kernel.org/linux-fsdevel/[email protected]/ > >> v3: > >> https://lore.kernel.org/linux-fsdevel/[email protected]/ > >> v2: > >> https://lore.kernel.org/linux-fsdevel/[email protected]/ > >> v1: https://lore.kernel.org/linux-fsdevel/ak5GfvVfWLJU1EwK@debian/ > >> Documentation/filesystems/erofs.rst | 15 ++++++ > >> fs/erofs/super.c | 73 ++++++++++++++++++++++++----- > >> 2 files changed, 77 insertions(+), 11 deletions(-) > >> diff --git a/Documentation/filesystems/erofs.rst > >> b/Documentation/filesystems/erofs.rst > >> index 4230884fb359..774e8b236d09 100644 > >> --- a/Documentation/filesystems/erofs.rst > >> +++ b/Documentation/filesystems/erofs.rst > >> @@ -139,6 +139,21 @@ inode_share Enable inode page sharing for > >> this filesystem. Inodes wi > >> page cache. > >> =================== > >> ========================================================= > >> +File-backed mounts > >> +================== > >> + > >> +When CONFIG_EROFS_FS_BACKED_BY_FILE is enabled, EROFS file-backed images > >> +can be mounted directly without a loopback block device. The backing file > >> +can be given either as a path, or as an already-opened file descriptor. > >> + > >> +When a file descriptor is used, the kernel resolves its path and records > >> it > >> +so that /proc/mounts and similar interfaces can still report the mount > >> +source. > >> + > >> +Only regular files are accepted as backing files; to mount an image that > >> +resides on a block device, use the traditional block device mount path > >> +instead. > > > > Do we need to add an entry to describe the new mount option source= in > > "Mount options" section in erofs.rst? > > > > Thanks, > > I've another patch "erofs: reuse superblock for file-backed mounts" that > also touches erofs.rst and it is currently based on top of this version. > I wonder what is your preferred way to handle them.
EROFS dev branch usually has a small number of patches. Since Chao gave a new suggestion, I think a v6 is needed (but you could add all previous reviewed-by:). And "erofs: reuse superblock for file-backed mounts" needs to be rebased too, I will find time to play with it this week (or you could add a testcase in erofs-utils experimental-tests if you have time.) > > Will maintainers deal with conflicts or do I need to submit them as a > single series? > > Do you prefer a new submission v6 with the following fixup? > > diff --git a/Documentation/filesystems/erofs.rst > b/Documentation/filesystems/erofs.rst > index c972a869f3e9..49c4e7dbc5d6 100644 > --- a/Documentation/filesystems/erofs.rst > +++ b/Documentation/filesystems/erofs.rst > @@ -137,6 +137,8 @@ fsoffset=%llu Specify block-aligned filesystem > offset for the primary d > inode_share Enable inode page sharing for this filesystem. > Inodes with > identical content within the same domain ID can share > the > page cache. > +source=%s (For file-backed mounts) Specify the backing image as > a path > + or as an already-opened file descriptor. Not quite sure "an already-opened file descriptor" is "%s", but I'm fine since it's quite a minor one (it's unneeded to nitpick the documentation). Thanks, Gao Xiang > > Thanks, > Giuseppe > >
