On Thu, Jul 11, 2024 at 10:21:35AM +0200, Hanna Czenczek wrote: > On 10.07.24 20:42, Josef Bacik wrote: > > On Wed, Jul 10, 2024 at 09:28:08AM +0200, Hanna Czenczek wrote: > > > On 09.07.24 19:56, Josef Bacik wrote: > > > > On Tue, Jul 09, 2024 at 01:19:16PM +0200, Hanna Czenczek wrote: > > > > > Hi, > > > > > > > > > > We want to be able to mount filesystems that just consist of one regular > > > > > file via virtio-fs, i.e. no root directory, just a file as the root > > > > > node. > > > > > > > > > > While that is possible via FUSE itself (through the 'rootmode' mount > > > > > option, which is automatically set by the fusermount help program to > > > > > match the mount point's inode mode), there is no virtio-fs option yet > > > > > that would allow changing the rootmode from S_IFDIR to S_IFREG. > > > > > > > > > > To do that, this series introduces a new 'file' mount option that does > > > > > precisely that. Alternatively, we could provide the same 'rootmode' > > > > > option that FUSE has, but as laid out in patch 1's commit description, > > > > > that option is a bit cumbersome for virtio-fs (in a way that it is not > > > > > for FUSE), and its usefulness as a more general option is limited. > > > > > > > > > All this does is make file an alias for something a little easier for users to > > > > read, which can easily be done in libfuse. Add the code to lib/mount.c to alias > > > > 'file' to turn it into rootmode=S_IFREG when it sends it to the kernel, it's not > > > > necessary to do this in the kernel. Thanks, > > > This series is not about normal FUSE filesystems (file_system_type > > > fuse_fs_type, “fuse”), but about virtio-fs (file_system_type virtio_fs_type, > > > “virtiofs”), i.e. a case where libfuse and fusermount are not involved at > > > all. As far as I’m aware, mounting a virtio-fs filesystem with a > > > non-directory root inode is currently not possible at all. > > Ok so I think I had it backwards in my head, my apologies. > > > > That being said I still don't understand why this requires a change to virtiofs > > at all. > > > > I have a virtiofs thing attached to my VM. Inside the vm I do > > > > mount -t virtiofs <name of thing I've attached to the vm> /directory > > > > and then on the host machine, virtiofsd is a "normal" FUSE driver, except it's > > talking over the socket you setup between the guest and the host. I assume this > > is all correct? > > > > So then the question is, why does it matter what virtiofsd is exposing? I guess > > that's the better question. The guest shouldn't have to care if it's a > > directory or a file right? The mountpoint is going to be a directory, whatever > > is backing it shouldn't matter. Could you describe the exact thing you're > > trying to accomplish? Thanks, > > The mount point needs to be of the same mode as the root node of the mounted > filesystem, or it’ll be inaccessible after mounting[1]. In this case, I > want to export a regular file as the root node, so the root node must be a > regular file, too: > > host$ echo foo > /tmp/bar > > host$ virtiofsd --shared-dir /tmp/bar --socket-path /tmp/viofsd.sock > --sandbox none > > > guest# mkdir /tmp/mnt-dir > > guest# mount -t virtiofs virtiofs-tag /tmp/mnt-dir > > guest# stat /tmp/mnt-dir > stat: cannot statx '/tmp/mnt-dir': Input/output error > > guest# cat /tmp/mnt-dir > cat: /tmp/mnt-dir: Input/output error > > guest# ls /tmp/mnt-dir > ls: cannot access '/tmp/mnt-dir': Input/output error > > guest# umount /tmp/mnt-dir > > (following with this series applied) > > guest# touch /tmp/mnt-file > > guest# mount -t virtiofs virtiofs-tag /tmp/mnt-file -o file > > guest# stat /tmp/mnt-file > File: /tmp/mnt-file > Size: 4 Blocks: 8 IO Block: 4096 regular file > [...] > > guest# cat /tmp/mnt-file > foo > > guest# ls --file-type /tmp/mnt-file > /tmp/mnt-file > > guest# ls --file-type /tmp > mnt-dir/ > mnt-file > [...] > Got it, this makes sense, thanks for explaining it to me. You can add Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Thanks, Josef
