Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[Trond Myklebust <trond.myklebust@primarydata.com>]

On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan@intel.com> wrote:

> From: David Howells <dhowells@redhat.com>
> 
> Make __d_materialise_dentry() set the materialised dentry name correctly by
> flipping the arguments to switch_names().
> 
> switch_names() is lazy: if both names are internal to their dentries, it'll
> overwrite that of the first dentry with that of the second, and won't update
> that of the second.
> 
> In the case of __d_materialise_dentry(), the second is an already extant
> anonymous dentry that we want to insert into the tree in place of the dentry we
> just looked up[*].  However, the dentry we just looked up carries the name we
> actually want to use.
> 
> [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> nearer the root when the two meet, where both mounts share a superblock and
> thus a set of dentries.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> fs/dcache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 265e0ce..ff779d4 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> 
> 	dparent = dentry->d_parent;
> 
> -	switch_names(dentry, anon);
> +	switch_names(anon, dentry);
> 	swap(dentry->d_name.hash, anon->d_name.hash);
> 
> 	dentry->d_parent = dentry;

Well spotted...

We ought to better document the fact that ’switch_names’ is asymmetrical. Perhaps change it to ‘update_target_name’, and then switch the argument names so that the ’target’ really is the thing that gets updated?

_________________________________
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com

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