On Tue, Mar 22, 2016 at 04:51:47PM -0400, Benjamin Coddington wrote:
> On Tue, 22 Mar 2016, J. Bruce Fields wrote:
>
> > Possibly overkill, but I think I'll fold in something like this if you
> > don't see an objection.
>
> No objection. To answer your earlier question (does the client even send a
> read if it would extend past the size returned from a recent getattr?):
>
> Looks to me (by testing with a server that never sets eof) the answer is no.
> The client won't issue reads beyond the end of the file.
>
> Also the previous patch's subject is now a little misleading. Maybe
> s/rather than/as well as/ would do.
OK.--b.
>
> Ben
>
> > commit 58e18a2a14a0
> > Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> > Date: Tue Mar 22 14:08:11 2016 -0400
> >
> > nfsd: document read eof logic
> >
> > The choice of checks here is a little subtle, let's document this for
> > posterity.
> >
> > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> >
> > diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> > index 83c9abb33e8b..df0f0a86f21d 100644
> > --- a/fs/nfsd/nfs3proc.c
> > +++ b/fs/nfsd/nfs3proc.c
> > @@ -168,8 +168,7 @@ nfsd3_proc_read(struct svc_rqst *rqstp, struct nfsd3_readargs *argp,
> > &resp->count);
> > if (nfserr == 0) {
> > struct inode *inode = d_inode(resp->fh.fh_dentry);
> > - resp->eof = (cnt > resp->count) ||
> > - ((argp->offset + resp->count) >= inode->i_size);
> > + resp->eof = nfsd_eof_on_read(cnt, resp->count, argp->offset, inode->i_size);
> > }
> >
> > RETURN_STATUS(nfserr);
> > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > index 90232bd7e498..9df898ba648f 100644
> > --- a/fs/nfsd/nfs4xdr.c
> > +++ b/fs/nfsd/nfs4xdr.c
> > @@ -3387,8 +3387,8 @@ static __be32 nfsd4_encode_splice_read(
> > return nfserr;
> > }
> >
> > - eof = (len > maxcount) ||
> > - ((read->rd_offset + maxcount >= d_inode(read->rd_fhp->fh_dentry)->i_size));
> > + eof = nfsd_eof_on_read(len, maxcount, read->rd_offset,
> > + d_inode(read->rd_fhp->fh_dentry)->i_size);
> >
> > *(p++) = htonl(eof);
> > *(p++) = htonl(maxcount);
> > @@ -3465,8 +3465,8 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
> > return nfserr;
> > xdr_truncate_encode(xdr, starting_len + 8 + ((maxcount+3)&~3));
> >
> > - eof = (len > maxcount) ||
> > - ((read->rd_offset + maxcount >= d_inode(read->rd_fhp->fh_dentry)->i_size));
> > + eof = nfsd_eof_on_read(len, maxcount, read->rd_offset,
> > + d_inode(read->rd_fhp->fh_dentry)->i_size);
> >
> > tmp = htonl(eof);
> > write_bytes_to_xdr_buf(xdr->buf, starting_len , &tmp, 4);
> > diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> > index c11ba316f23f..6244e073c137 100644
> > --- a/fs/nfsd/vfs.h
> > +++ b/fs/nfsd/vfs.h
> > @@ -139,4 +139,24 @@ static inline int nfsd_create_is_exclusive(int createmode)
> > || createmode == NFS4_CREATE_EXCLUSIVE4_1;
> > }
> >
> > +static inline bool nfsd_eof_on_read(long requested, long read,
> > + loff_t offset, loff_t size)
> > +{
> > + /* We assume a short read means eof: */
> > + if (requested > read)
> > + return true;
> > + /*
> > + * A non-short read might also reach end of file. The spec
> > + * still requires us to set eof in that case.
> > + *
> > + * Further operations may have modified the file size since
> > + * the read, so the following check is not atomic with the read.
> > + * The only case we've seen that cause a problem for a client
> > + * is the case where the read returned a count of 0 without
> > + * setting eof. That case was fixed by the addition of the
> > + * above check.
> > + */
> > + return (offset + read >= size);
> > +}
> > +
> > #endif /* LINUX_NFSD_VFS_H */
> >
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