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From:   Ignat Korchagin <ignat@cloudflare.com>
Date:   Mon, 10 Jul 2023 19:43:00 +0100
Message-ID: <CALrw=nHZhczbY0BOOieTCMnYM8AnobU4ka+wfoOO+uxA9=pMjw@mail.gmail.com>
Subject: Re: [PATCH] kernfs: attach uuid for every kernfs and report it in fsid
To:     Ivan Babrou <ivan@cloudflare.com>
Cc:     linux-fsdevel@vger.kernel.org, kernel-team@cloudflare.com,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Amir Goldstein <amir73il@gmail.com>,
        Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>
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On Mon, Jul 10, 2023 at 7:33=E2=80=AFPM Ivan Babrou <ivan@cloudflare.com> w=
rote:
>
> The following two commits added the same thing for tmpfs:
>
> * commit 2b4db79618ad ("tmpfs: generate random sb->s_uuid")
> * commit 59cda49ecf6c ("shmem: allow reporting fanotify events with file =
handles on tmpfs")
>
> Having fsid allows using fanotify, which is especially handy for cgroups,
> where one might be interested in knowing when they are created or removed=
.
>
> Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
> ---
>  fs/kernfs/mount.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index d49606accb07..930026842359 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -16,6 +16,8 @@
>  #include <linux/namei.h>
>  #include <linux/seq_file.h>
>  #include <linux/exportfs.h>
> +#include <linux/uuid.h>
> +#include <linux/statfs.h>
>
>  #include "kernfs-internal.h"
>
> @@ -45,8 +47,15 @@ static int kernfs_sop_show_path(struct seq_file *sf, s=
truct dentry *dentry)
>         return 0;
>  }
>
> +int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)

This probably should be declared static

> +{
> +       simple_statfs(dentry, buf);
> +       buf->f_fsid =3D uuid_to_fsid(dentry->d_sb->s_uuid.b);
> +       return 0;
> +}
> +
>  const struct super_operations kernfs_sops =3D {
> -       .statfs         =3D simple_statfs,
> +       .statfs         =3D kernfs_statfs,
>         .drop_inode     =3D generic_delete_inode,
>         .evict_inode    =3D kernfs_evict_inode,
>
> @@ -351,6 +360,8 @@ int kernfs_get_tree(struct fs_context *fc)
>                 }
>                 sb->s_flags |=3D SB_ACTIVE;
>
> +               uuid_gen(&sb->s_uuid);
> +
>                 down_write(&root->kernfs_supers_rwsem);
>                 list_add(&info->node, &info->root->supers);
>                 up_write(&root->kernfs_supers_rwsem);
> --
> 2.41.0
>

Ignat