VFS: New /proc file /proc/self/mountstats

Create a new file under /proc/self, called mountstats, where mounted file
systems can export information (configuration options, performance counters,
and so on).  Use a mechanism similar to /proc/mounts and s_ops->show_options.

This mechanism does not violate namespace security, and is safe to use while
other processes are unmounting file systems.

Thanks to Mike Waychison for his review and comments.

Test-plan:
Test concurrent mount/unmount operations while cat'ing /proc/self/mountstats.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 128d0082522c..be21e860a9f2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1086,6 +1086,7 @@ struct super_operations {
         void (*umount_begin) (struct super_block *);
 
         int (*show_options)(struct seq_file *, struct vfsmount *);
+        int (*show_stats)(struct seq_file *, struct vfsmount *);
 
         ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
         ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);