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From:   Ivan Babrou <ivan@cloudflare.com>
To:     linux-fsdevel@vger.kernel.org
Cc:     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>,
        Ivan Babrou <ivan@cloudflare.com>
Subject: [PATCH] kernfs: attach uuid for every kernfs and report it in fsid
Date:   Mon, 10 Jul 2023 11:33:38 -0700
Message-ID: <20230710183338.58531-1-ivan@cloudflare.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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, struct dentry *dentry)
 	return 0;
 }
 
+int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	simple_statfs(dentry, buf);
+	buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
+	return 0;
+}
+
 const struct super_operations kernfs_sops = {
-	.statfs		= simple_statfs,
+	.statfs		= kernfs_statfs,
 	.drop_inode	= generic_delete_inode,
 	.evict_inode	= kernfs_evict_inode,
 
@@ -351,6 +360,8 @@ int kernfs_get_tree(struct fs_context *fc)
 		}
 		sb->s_flags |= 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