Re: [PATCH v9 13/19] nfsd: add "localio" support

[Mike Snitzer <snitzer@kernel.org>]

On Sun, Jun 30, 2024 at 10:49:51AM -0400, Chuck Lever wrote:
> On Sat, Jun 29, 2024 at 06:18:42PM -0400, Chuck Lever wrote:
> > > +
> > > +	/* nfs_fh -> svc_fh */
> > > +	if (nfs_fh->size > NFS4_FHSIZE) {
> > > +		status = -EINVAL;
> > > +		goto out;
> > > +	}
> > > +	fh_init(&fh, NFS4_FHSIZE);
> > > +	fh.fh_handle.fh_size = nfs_fh->size;
> > > +	memcpy(fh.fh_handle.fh_raw, nfs_fh->data, nfs_fh->size);
> > > +
> > > +	if (fmode & FMODE_READ)
> > > +		mayflags |= NFSD_MAY_READ;
> > > +	if (fmode & FMODE_WRITE)
> > > +		mayflags |= NFSD_MAY_WRITE;
> > > +
> > > +	beres = nfsd_file_acquire(rqstp, &fh, mayflags, &nf);
> > > +	if (beres) {
> > > +		status = nfs_stat_to_errno(be32_to_cpu(beres));
> > > +		goto out_fh_put;
> > > +	}
> > 
> > So I'm wondering whether just calling fh_verify() and then
> > nfsd_open_verified() would be simpler and/or good enough here. Is
> > there a strong reason to use the file cache for locally opened
> > files? Jeff, any thoughts?
> 
> > Will there be writeback ramifications for
> > doing this? Maybe we need a comment here explaining how these files
> > are garbage collected (just an fput by the local I/O client, I would
> > guess).
> 
> OK, going back to this: Since right here we immediately call 
> 
> 	nfsd_file_put(nf);
> 
> There are no writeback ramifications nor any need to comment about
> garbage collection. But this still seems like a lot of (possibly
> unnecessary) overhead for simply obtaining a struct file.

Easy enough change, probably best to avoid the filecache but would like
to verify with Jeff before switching:

diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c
index 1d6508aa931e..85ebf63789fb 100644
--- a/fs/nfsd/localio.c
+++ b/fs/nfsd/localio.c
@@ -197,7 +197,6 @@ int nfsd_open_local_fh(struct net *cl_nfssvc_net,
        const struct cred *save_cred;
        struct svc_rqst *rqstp;
        struct svc_fh fh;
-       struct nfsd_file *nf;
        __be32 beres;

        if (nfs_fh->size > NFS4_FHSIZE)
@@ -235,13 +234,12 @@ int nfsd_open_local_fh(struct net *cl_nfssvc_net,
        if (fmode & FMODE_WRITE)
                mayflags |= NFSD_MAY_WRITE;

-       beres = nfsd_file_acquire(rqstp, &fh, mayflags, &nf);
+       beres = fh_verify(rqstp, &fh, S_IFREG, mayflags);
        if (beres) {
                status = nfs_stat_to_errno(be32_to_cpu(beres));
                goto out_fh_put;
        }
-       *pfilp = get_file(nf->nf_file);
-       nfsd_file_put(nf);
+       status = nfsd_open_verified(rqstp, &fh, mayflags, pfilp);
 out_fh_put:
        fh_put(&fh);
        nfsd_local_fakerqst_destroy(rqstp);

Mike