Re: [patch 3/6] fs: dcache remove d_mounted

Ian Kent
2009-10-15T10:37:57Z

On Thu, Oct 15, 2009 at 03:40:29PM +1100, npiggin@suse.de wrote:
> Rather than keep a d_mounted count in the dentry (which is only used to
> speculatively take a look in the mount hash table if it is non-zero), set a
> dentry flag instead. The flag can be cleared by checking the hash table to see
> if there are any mounts left. It is not time critical because it is performed
> at detach time.
>
> This saves 4 bytes on 32-bit, nothing on 64-bit but it does provide a hole I
> might use later (and some configs have larger than 32-bit spinlocks which might
> make use of the hole).
>
> Autofs4 conversion and changelog by Ian Kent <raven@themaw.net>:
> In autofs4, when expring direct (or offset) mounts we need to ensure that we
> block user path walks into the autofs mount, which is covered by another mount.
> To do this we clear the mounted status so that follows stop before walking into
> the mount and are essentially blocked until the expire is completed. The
> automount daemon still finds the correct dentry for the umount due to the
> follow mount logic in fs/autofs4/root.c:autofs4_follow_link(), which is set as
> an inode operation for direct and offset mounts only and is called following
> the lookup that stopped at the covered mount.
>
> At the end of the expire the covering mount probably has gone away so the
> mounted status need not be restored. But we need to check this and only restore
> the mounted status if the expire failed.
>
> Signed-off-by: Nick Piggin <npiggin@suse.de>

For the autofs4 bits.

Acked-by: Ian Kent <raven@themaw.net>