Re: [Qemu-devel] [PATCH v7 0/3] 9p: Fix file ID collisions

[Greg Kurz]

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... :-\

--
Greg