NFS: Introduce iovec I/O helpers to fs/nfs/direct.c

Add helpers that iterate over multi-segment iovecs.  These will
be used to support multi-segment scatter/gather direct I/O in a
later patch.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/direct.c

@@ -355,6 +355,41 @@ static ssize_t nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned lo
 	return result < 0 ? (ssize_t) result : -EFAULT;
 }
 
+static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
+					      const struct iovec *iov,
+					      unsigned long nr_segs,
+					      loff_t pos)
+{
+	ssize_t result = -EINVAL;
+	size_t requested_bytes = 0;
+	unsigned long seg;
+
+	get_dreq(dreq);
+
+	for (seg = 0; seg < nr_segs; seg++) {
+		const struct iovec *vec = &iov[seg];
+		result = nfs_direct_read_schedule(dreq,
+					(unsigned long)vec->iov_base,
+						  vec->iov_len, pos);
+		if (result < 0)
+			break;
+		requested_bytes += result;
+		if ((size_t)result < vec->iov_len)
+			break;
+		pos += vec->iov_len;
+	}
+
+	if (put_dreq(dreq))
+		nfs_direct_complete(dreq);
+
+	if (requested_bytes != 0)
+		return 0;
+
+	if (result < 0)
+		return result;
+	return -EIO;
+}
+
 static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
 {
 	ssize_t result = 0;
@@ -697,6 +732,42 @@ static ssize_t nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned l
 	return result < 0 ? (ssize_t) result : -EFAULT;
 }
 
+static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
+					       const struct iovec *iov,
+					       unsigned long nr_segs,
+					       loff_t pos, int sync)
+{
+	ssize_t result = 0;
+	size_t requested_bytes = 0;
+	unsigned long seg;
+
+	get_dreq(dreq);
+
+	for (seg = 0; seg < nr_segs; seg++) {
+		const struct iovec *vec = &iov[seg];
+		result = nfs_direct_write_schedule(dreq,
+					(unsigned long)vec->iov_base,
+						   vec->iov_len,
+						   pos, sync);
+		if (result < 0)
+			break;
+		requested_bytes += result;
+		if ((size_t)result < vec->iov_len)
+			break;
+		pos += vec->iov_len;
+	}
+
+	if (put_dreq(dreq))
+		nfs_direct_write_complete(dreq, dreq->inode);
+
+	if (requested_bytes != 0)
+		return 0;
+
+	if (result < 0)
+		return result;
+	return -EIO;
+}
+
 static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
 {
 	ssize_t result = 0;