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Re: virtio-fs: Fix file ID collisions (was: 9p: Fix file ID collisions)
From: |
Dr. David Alan Gilbert |
Subject: |
Re: virtio-fs: Fix file ID collisions (was: 9p: Fix file ID collisions) |
Date: |
Wed, 16 Oct 2019 14:44:09 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Christian Schoenebeck (address@hidden) wrote:
> On Dienstag, 15. Oktober 2019 11:20:39 CEST Greg Kurz wrote:
> > On Tue, 08 Oct 2019 14:05:28 +0200
> >
> > Christian Schoenebeck <address@hidden> wrote:
> > > I wonder though whether virtio-fs suffers from the same file ID collisions
> > > problem when sharing multiple file systems.
> >
> > I gave a try and it seems that virtio-fs might expose the inode numbers from
> > different devices in the host, unvirtualized AND with the same device in
> > the guest:
> >
> > # mkdir -p /var/tmp/virtio-fs/proc
> > # mount --bind /proc /var/tmp/virtio-fs/proc
> > # virtiofsd -o vhost_user_socket=/tmp/vhostqemu -o source=/var/tmp/virtio-fs
> > -o cache=always
> >
> > and then started QEMU with:
> >
> > -chardev socket,id=char0,path=/tmp/vhostqemu \
> > -device vhost-user-fs-pci,queue-size=1024,chardev=char0,tag=myfs \
> > -m 4G -object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on
> > \ -numa node,memdev=mem
> >
> > In the host:
> >
> > $ stat /var/tmp/virtio-fs
> > File: /var/tmp/virtio-fs
> > Size: 4096 Blocks: 8 IO Block: 4096 directory
> > Device: fd00h/64768d Inode: 787796 Links: 4
> > Access: (0775/drwxrwxr-x) Uid: ( 1000/ greg) Gid: ( 1000/ greg)
> > Context: unconfined_u:object_r:user_tmp_t:s0
> > Access: 2019-10-15 11:08:52.070080922 +0200
> > Modify: 2019-10-15 11:02:09.887404446 +0200
> > Change: 2019-10-15 11:02:09.887404446 +0200
> > Birth: 2019-10-13 19:13:04.009699354 +0200
> > [greg@bahia ~]$ stat /var/tmp/virtio-fs/FOO
> > File: /var/tmp/virtio-fs/FOO
> > Size: 0 Blocks: 0 IO Block: 4096 regular empty
> > file Device: fd00h/64768d Inode: 790740 Links: 1
> > Access: (0664/-rw-rw-r--) Uid: ( 1000/ greg) Gid: ( 1000/ greg)
> > Context: unconfined_u:object_r:user_tmp_t:s0
> > Access: 2019-10-15 11:02:09.888404448 +0200
> > Modify: 2019-10-15 11:02:09.888404448 +0200
> > Change: 2019-10-15 11:02:09.888404448 +0200
> > Birth: 2019-10-15 11:02:09.887404446 +0200
> > [greg@bahia ~]$ stat /var/tmp/virtio-fs/proc/fs
> > File: /var/tmp/virtio-fs/proc/fs
> > Size: 0 Blocks: 0 IO Block: 1024 directory
> > Device: 4h/4d Inode: 4026531845 Links: 5
> > Access: (0555/dr-xr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
> > Context: system_u:object_r:proc_t:s0
> > Access: 2019-10-01 14:50:09.223233901 +0200
> > Modify: 2019-10-01 14:50:09.223233901 +0200
> > Change: 2019-10-01 14:50:09.223233901 +0200
> > Birth: -
> >
> > In the guest:
> >
> > [greg@localhost ~]$ stat /mnt
> > File: /mnt
> > Size: 4096 Blocks: 8 IO Block: 4096 directory
> > Device: 2dh/45d Inode: 787796 Links: 4
> > Access: (0775/drwxrwxr-x) Uid: ( 1000/ greg) Gid: ( 1000/ greg)
> > Context: system_u:object_r:unlabeled_t:s0
> > Access: 2019-10-15 11:08:52.070080922 +0200
> > Modify: 2019-10-15 11:02:09.887404446 +0200
> > Change: 2019-10-15 11:02:09.887404446 +0200
> > Birth: -
> > [greg@localhost ~]$ stat /mnt/FOO
> > File: /mnt/FOO
> > Size: 0 Blocks: 0 IO Block: 4096 regular empty
> > file Device: 2dh/45d Inode: 790740 Links: 1
> > Access: (0664/-rw-rw-r--) Uid: ( 1000/ greg) Gid: ( 1000/ greg)
> > Context: system_u:object_r:unlabeled_t:s0
> > Access: 2019-10-15 11:02:09.888404448 +0200
> > Modify: 2019-10-15 11:02:09.888404448 +0200
> > Change: 2019-10-15 11:02:09.888404448 +0200
> > Birth: -
> > [greg@localhost ~]$ stat /mnt/proc/fs
> > File: /mnt/proc/fs
> > Size: 0 Blocks: 0 IO Block: 1024 directory
> > Device: 2dh/45d Inode: 4026531845 Links: 5
> > Access: (0555/dr-xr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
> > Context: system_u:object_r:unlabeled_t:s0
> > Access: 2019-10-01 14:50:09.223233901 +0200
> > Modify: 2019-10-01 14:50:09.223233901 +0200
> > Change: 2019-10-01 14:50:09.223233901 +0200
> > Birth: -
> >
> > Unless I'm missing something, it seems that "virtio-fs" has the same
> > issue we had on 9pfs before Christian's patches... :-\
>
> Is a fix for this desired for virtio-fs?
Yes I think so; we had originally thought we were hiding the host inode
numbers; but that's not true - since we pass both a device and inode
number in virtiofs, unlike 9p, it seems we can probably get away with
only remapping device IDs rather than inode numbers; but that requires
some understanding of how multiple block device IDs are supposed to look
like to the guest kernel.
Dave
> Greg, did you have to update kernel version on either host or guest side to
> get virtio-fs running? Or were the discussed kernel changes just for optional
> acceleration purposes (i.e. DAX)?
>
> Best regards,
> Christian Schoenebeck
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK