Re: [PATCH v4 1/5] NFSD: filecache: add STATX_DIOALIGN and STATX_DIO_READ_ALIGN support

[Mike Snitzer <snitzer@kernel.org>]

On Wed, Jul 23, 2025 at 03:06:00PM -0400, Mike Snitzer wrote:
> On Wed, Jul 23, 2025 at 02:58:19PM -0400, Jeff Layton wrote:
> > On Wed, 2025-07-23 at 11:43 -0400, Mike Snitzer wrote:
> > > Use STATX_DIOALIGN and STATX_DIO_READ_ALIGN to get and store DIO
> > > alignment attributes from underlying filesystem in associated
> > > nfsd_file.  This is done when the nfsd_file is first opened for
> > > a regular file.
> > > 
> > > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > > ---
> > >  fs/nfsd/filecache.c | 32 ++++++++++++++++++++++++++++++++
> > >  fs/nfsd/filecache.h |  4 ++++
> > >  fs/nfsd/nfsfh.c     |  4 ++++
> > >  3 files changed, 40 insertions(+)
> > > 
> > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> > > index 8581c131338b..5447dba6c5da 100644
> > > --- a/fs/nfsd/filecache.c
> > > +++ b/fs/nfsd/filecache.c
> > > @@ -231,6 +231,9 @@ nfsd_file_alloc(struct net *net, struct inode *inode, unsigned char need,
> > >  	refcount_set(&nf->nf_ref, 1);
> > >  	nf->nf_may = need;
> > >  	nf->nf_mark = NULL;
> > > +	nf->nf_dio_mem_align = 0;
> > > +	nf->nf_dio_offset_align = 0;
> > > +	nf->nf_dio_read_offset_align = 0;
> > >  	return nf;
> > >  }
> > >  
> > > @@ -1048,6 +1051,33 @@ nfsd_file_is_cached(struct inode *inode)
> > >  	return ret;
> > >  }
> > >  
> > > +static __be32
> > > +nfsd_file_getattr(const struct svc_fh *fhp, struct nfsd_file *nf)
> > > +{
> > > +	struct inode *inode = file_inode(nf->nf_file);
> > > +	struct kstat stat;
> > > +	__be32 status;
> > > +
> > > +	/* Currently only need to get DIO alignment info for regular files */
> > > +	if (!S_ISREG(inode->i_mode))
> > > +		return nfs_ok;
> > > +
> > > +	status = fh_getattr(fhp, &stat);
> > > +	if (status != nfs_ok)
> > > +		return status;
> > > +
> > > +	if (stat.result_mask & STATX_DIOALIGN) {
> > > +		nf->nf_dio_mem_align = stat.dio_mem_align;
> > > +		nf->nf_dio_offset_align = stat.dio_offset_align;
> > > +	}
> > > +	if (stat.result_mask & STATX_DIO_READ_ALIGN)
> > > +		nf->nf_dio_read_offset_align = stat.dio_read_offset_align;
> > > +	else
> > > +		nf->nf_dio_read_offset_align = nf->nf_dio_offset_align;
> > > +
> > > +	return status;
> > > +}
> > > +
> > >  static __be32
> > >  nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net,
> > >  		     struct svc_cred *cred,
> > > @@ -1166,6 +1196,8 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net,
> > >  			}
> > >  			status = nfserrno(ret);
> > >  			trace_nfsd_file_open(nf, status);
> > > +			if (status == nfs_ok)
> > > +				status = nfsd_file_getattr(fhp, nf);
> > 
> > 
> > Doing a getattr alongside every open could be expensive in some
> > configurations (like reexported NFS). We may want to skip doing this
> > getattr this if O_DIRECT isn't is use. Is that possible?
> 
> Good point, yes, should be easy enough.  Will depend on the debugfs
> knobs, so will tack a patch on at the end.

What is the best way to check for NFSD reexporting NFS?

I've done stuff like that as a side-effect of setting/checking a
particular flag, e.g. commit 5cca2483b9fd ("nfsd: disallow file
locking and delegations for NFSv4 reexport")

But not immediately seeing a more generic way to do the check...

Thanks,
Mike