Re: [PATCH 1/5] nfsd: bypass readahead cache when have struct file

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jul 29, 2010 at 06:21:20PM -0400, J. Bruce Fields wrote:
> The readahead cache compensates for the fact that the NFS server
> currently does an open and close on every IO operation in the NFSv2 and
> NFSv3 case.
> 
> In the NFSv4 case we have long-lived struct files associated with client
> opens, so there's no need for this.  In fact, concurrent IO's using
> trying to modify the same file->f_ra may cause problems.

Interesting.  So why did we get these for v4, but not a file handle
cache for v2 and v3 at the same time?  That would make life for the
filesystems a lot easier.

>  		if (err)
>  			goto out;
>  		err = nfsd_vfs_read(rqstp, fhp, file, offset, vec, vlen, count);
> -	} else {
> -		err = nfsd_open(rqstp, fhp, S_IFREG, NFSD_MAY_READ, &file);
> -		if (err)
> -			goto out;
> -		err = nfsd_vfs_read(rqstp, fhp, file, offset, vec, vlen, count);
> -		nfsd_close(file);
> -	}
> +	} else
> +		err = nfsd_open_read(rqstp, fhp, offset, vec, vlen, count);

The callers of nfsd_read are:

fs/nfsd/nfs3proc.c:     nfserr = nfsd_read(rqstp, &resp->fh, NULL,
fs/nfsd/nfs4proc.c:     /* no need to check permission - this will be done in nfsd_read() */
fs/nfsd/nfs4xdr.c:      nfserr = nfsd_read(read->rd_rqstp, read->rd_fhp, read->rd_filp,
fs/nfsd/nfsproc.c:      nfserr = nfsd_read(rqstp, fh_copy(&resp->fh, &argp->fh), NULL,

which suggests that we're better off just calling nfsd_open_read
(possible with a better name) directly from fs/nfsd/nfs3proc.c and
fs/nfsd/nfsproc.c and nfsd_vfs_read directly from fs/nfsd/nfs4proc.c
and fs/nfsd/nfs4xdr.c instead of doing this conditional.