Possibly overkill, but I think I'll fold in something like this if you
don't see an objection.
--b.
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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