Re: [PATCH] xfs: revert to double-buffering readdir

[Christoph Hellwig <hch@infradead.org>]

On Fri, Nov 30, 2007 at 04:36:25PM -0600, Stephen Lord wrote:
> Wow, was it really that long ago!
>
> Looks like the readdir is in the bowels of the btree code when filldir gets 
> called
> here, there are probably locks on several buffers in the btree at this 
> point. This
> will only show up for large directories I bet.

Chris saw it with block-form directories.  I've verified it works fine
with short-form directories, and the leaf code looks like it could
happen aswell.  I also remember gfs2 running into a similar problem.

> The xfs readdir code has the complete xfs inode number in its hands at this 
> point
> (filldir is not necessarily getting all the bits of it). All we are doing 
> the lookup
> for really is to get the inode number back again so we can get the inode
> and get the attributes. Rather dumb really. There has got to be a way of
> doing a callout structure here so that the inode number can be pushed
> through filldir and back into an fs specific call. The fs then can do a 
> lookup
> by id - which is what it does most of the time for resolving nfs handles
> anyway. Should be more efficient than the current scheme.

Yes, a lot more efficient.  But it means adding a new operation for use
by the nfs server.