kernfs: attach uuid for every kernfs and report it in fsid

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>
Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230731184731.64568-1-ivan@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index d49606accb07b1a702db70e17fdbd813a668a661..c4bf26142eec9baf2d955166ccb892705a1834a8 100644 (file)
--- 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;
 }
 
+static 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);