Return-Path: Date: Tue, 22 Mar 2016 17:22:11 -0400 From: "J. Bruce Fields" To: Benjamin Coddington Cc: Jeff Layton , linux-nfs@vger.kernel.org Subject: Re: [PATCH v2] nfsd: use short read rather than i_size to set eof Message-ID: <20160322212211.GJ4083@fieldses.org> References: <20160321213655.GB807@fieldses.org> <82e4c7a9756b21a4645421d04735ccf491b4296a.1458571329.git.bcodding@redhat.com> <20160322164624.GB4083@fieldses.org> <20160322185336.GD4083@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-ID: 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 > > 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 > > > > 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 */ > >