| Message ID | 20240709111918.31233-1-hreitz@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | virtio-fs: Add 'file' mount option | expand |
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, Josef
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. Hanna
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. > > > Hanna Czenczek (2): > virtio-fs: Add 'file' mount option > virtio-fs: Document 'file' mount option > > fs/fuse/virtio_fs.c | 9 ++++++++- > Documentation/filesystems/virtiofs.rst | 5 ++++- > 2 files changed, 12 insertions(+), 2 deletions(-) > > -- > 2.45.1 > Looks good to me. Maybe add the 'file' option to FUSE as well to keep them in sync (eventually rootmode could be exposed to virtiofs too, if necessary)? Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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, Josef
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 [...] [1] As far as I remember, FUSE/virtio-fs will present the root node’s mode as 'rootmode' during mounting, and so the d_is_dir() equality checks in do_move_mount() and graft_tree() just check whether that matches the mount point’s mode. So, like in the example above, mounting a filesystem whose root node is a regular file to a directory mount point without '-o file' succeeds. But accessing it then fails, probably because the mismatch is then noticed somewhere (virtiofsd receives a GETATTR request, that’s it), i.e. the root node is supposed to be a directory, but it turns out not to be after all. Hanna
On 10.07.24 19:28, Stefan Hajnoczi 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. >> >> >> Hanna Czenczek (2): >> virtio-fs: Add 'file' mount option >> virtio-fs: Document 'file' mount option >> >> fs/fuse/virtio_fs.c | 9 ++++++++- >> Documentation/filesystems/virtiofs.rst | 5 ++++- >> 2 files changed, 12 insertions(+), 2 deletions(-) >> >> -- >> 2.45.1 >> > Looks good to me. Maybe add the 'file' option to FUSE as well to keep > them in sync (eventually rootmode could be exposed to virtiofs too, if > necessary)? I don’t think this option makes much sense for FUSE, like Josef has said; it would just duplicate a subset of 'rootmode', and because FUSE filesystems are rarely mounted by hand, I don’t think anyone would ever use it. If it were important to keep them in sync, I’d rather have virtio-fs provide 'rootmode' instead. Personally, I don’t think it’s that important, and I’d rather have a simple '-o file' instead of '-o rootmode=0100000' (hope I counted the 0s right) for a filesystem that is actually not rarely mounted by hand. If we ever do find out that we want to support other root modes than S_IFREG and S_IFDIR, we will probably want 'rootmode' for virtio-fs, too, yes. But I can’t see that right now. > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Thanks! Hanna
On 11.07.24 10:21, Hanna Czenczek wrote: > On 10.07.24 20:42, Josef Bacik wrote: [...] >> 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: Sorry, I meant “[…], so the mount point must be a regular file, too”. Hanna
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@toxicpanda.com> Thanks, Josef
On 11.07.24 16:34, Josef Bacik wrote: > 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@toxicpanda.com> Thanks! Hanna
On Tue, 9 Jul 2024 at 13:19, Hanna Czenczek <hreitz@redhat.com> 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. I wonder if this is needed at all for virtiofs, which could easily do the FUSE_INIT request synchronously with mount(2) and the server could just tell the client the root mode explicitly in the FUSE_INIT reply, or could just fetch it with a separate FUSE_GETATTR. Why regular fuse doesn't do this? That's because a single threaded server can only be supported if the mount(2) syscall returns before any request need processing. Virtiofs doesn't suffer from this at all, AFAICS. Does this make sense? Thanks, Miklos
On 29.08.24 10:07, Miklos Szeredi wrote: > On Tue, 9 Jul 2024 at 13:19, Hanna Czenczek <hreitz@redhat.com> 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. > I wonder if this is needed at all for virtiofs, which could easily do > the FUSE_INIT request synchronously with mount(2) and the server could > just tell the client the root mode explicitly in the FUSE_INIT reply, > or could just fetch it with a separate FUSE_GETATTR. That would be great. I thought it would be necessary to install the superblock before sending FUSE_INIT, so I thought this wasn’t possible. I honestly have no idea how to go about it on a technical level, though. Naïvely, I think we’d need to split off the tail of fuse_fill_super_common() (everything starting from the fuse_get_root_inode() call) into a separate function, which in case of virtio-fs we’d call once we get the FUSE_INIT reply. (For non-virtio-fs, we could just call it immediately after fuse_fill_super_common().) But we can’t return from fuse_fill_super() until that root node is set up, can we? If so, we‘d need to await that FUSE_INIT reply in that function. Can we do that? > Why regular fuse doesn't do this? That's because a single threaded > server can only be supported if the mount(2) syscall returns before > any request need processing. Virtiofs doesn't suffer from this at > all, AFAICS. > > Does this make sense? It does! Hanna
On Thu, 29 Aug 2024 at 14:37, Hanna Czenczek <hreitz@redhat.com> wrote: > I honestly have no idea how to go about it on a technical level, > though. Naïvely, I think we’d need to split off the tail of > fuse_fill_super_common() (everything starting from the > fuse_get_root_inode() call) into a separate function, which in case of > virtio-fs we’d call once we get the FUSE_INIT reply. (For > non-virtio-fs, we could just call it immediately after > fuse_fill_super_common().) Yes, except I'm not sure it needs to be split, that depends on whether sending a request relies on any initialization in that function or not. > But we can’t return from fuse_fill_super() until that root node is set > up, can we? If so, we‘d need to await that FUSE_INIT reply in that > function. Can we do that? Sure, just need to send FUSE_INIT with fuse_simple_request() instead of fuse_simple_background(). Thanks, Miklos
On Thu, 29 Aug 2024 at 15:11, Hanna Czenczek <hreitz@redhat.com> wrote: > Hm, I thought we set some things in fuse_mount and fuse_conn in there that are then queried by fuse_send_init()... Maybe the only thing fuse_send_init() needs is fm->sb->s_bdi->ra_pages for max_readahead. Yes, that definitely needs special treatment. > Sounds simple. Do you think semantically it’s find to block here? We’d only do it for virtio-fs, so a denial-of-service may not be of concern here. It should be okay. AFAIK all network filesystems block mount(2) until setup is complete. Thanks, Miklos