[+fsdevel please CC on next versions]
On Wed, Mar 23, 2022 at 12:27 AM Gabriel Krisman Bertazi
<krisman@xxxxxxxxxxxxx> wrote:
>
> In order to expose tmpfs statistics on sysfs, add the boilerplate code
> to create the /sys/fs/tmpfs structure. Other filesystems usually do
> /sys/fs/<fs>/<disk>, but since this is a nodev filesystem, I'm proposing
> to use fsid as <disk>.
I am proposing st_dev minor.
>
> This takes care of not exposing SB_NOUSER mounts. I don't think we have
> a usecase for showing them and, since they don't appear elsewhere, they
> might be confusing to users.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
> ---
> include/linux/shmem_fs.h | 4 +++
> mm/shmem.c | 73 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 76 insertions(+), 1 deletion(-)
>
[...]
> +static int shmem_register_sysfs(struct super_block *sb)
> +{
> + int err;
> + struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
> + __kernel_fsid_t fsid = uuid_to_fsid(sb->s_uuid.b);
> +
> + init_completion(&sbinfo->s_kobj_unregister);
> + err = kobject_init_and_add(&sbinfo->s_kobj, &tmpfs_sb_ktype, shmem_root,
> + "%x%x", fsid.val[0], fsid.val[1]);
uuid (and fsid) try to be unique across tmpfs instances from different times.
You don't need that.
I think you'd rather use s_dev (minor number) which is unique among all tmpfs
instances at a given time and also much easier from user scripts to read from
(e.g. stat or /proc/self/mountinfo).
That's btw the same number is used as an entry in /sys/fs/fuse/connections
(fusectl pseudo fs).
Thanks,
Amir.
