Re: [PATCH v3 0/3] virtiofs: export filesystem tags through sysfs

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Feb 09, 2024 at 07:18:17AM -0500, Stefan Hajnoczi wrote:
> v3:
> - Use dev_dbg() to avoid spamming logs [Greg]
> - Fix 644 mode on "tag" attr and use __ATTR_RO() [Greg]
> - Use kset_uevent_ops and eliminate explicit KOBJ_REMOVE [Greg]
> v2:
> - Vivek mentioned that he didn't have time to work on this patch series
>   recently so I gave it a shot.
> - Information is now exposed in /sys/fs/virtiofs/ whereas before it was part of
>   the generic virtio device kobject, which didn't really fit.
> 
> Userspace needs a way to enumerate available virtiofs filesystems and detect
> when they are hotplugged or unplugged. This would allow systemd to wait for a
> virtiofs filesystem during boot, for example.
> 
> This patch series adds the following in sysfs:
> 
>   /sys/fs/virtiofs/<n>/tag    - unique identifier for mount(8)
>   /sys/fs/virtiofs/<n>/device - symlink to virtio device

Hi Stefan,

Thanks for the patches. I am glad you are solving this problem.

I am testing your patches. After boot, I see /sys/fs/virtiofs/ directory
but that directory is empty. No entries for any tags. I do have one
tag exported named "myfs" to the VM. And I can mount it.

Thanks
Vivek

> 
> A uevent is emitted when virtiofs devices are hotplugged or unplugged:
> 
>   KERNEL[111.113221] add      /fs/virtiofs/2 (virtiofs)
>   ACTION=add
>   DEVPATH=/fs/virtiofs/2
>   SUBSYSTEM=virtiofs
>   TAG=test
> 
>   KERNEL[165.527167] remove   /fs/virtiofs/2 (virtiofs)
>   ACTION=remove
>   DEVPATH=/fs/virtiofs/2
>   SUBSYSTEM=virtiofs
>   TAG=test
> 
> Stefan Hajnoczi (3):
>   virtiofs: forbid newlines in tags
>   virtiofs: export filesystem tags through sysfs
>   virtiofs: emit uevents on filesystem events
> 
>  fs/fuse/virtio_fs.c                         | 135 +++++++++++++++++---
>  Documentation/ABI/testing/sysfs-fs-virtiofs |  11 ++
>  2 files changed, 125 insertions(+), 21 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-fs-virtiofs
> 
> -- 
> 2.43.0
>