s3: smbd: Performance optimization for RECVFILE.

Based on work proposed by Jones <jones.kstw@gmail.com>.

Removes set_blocking()/set_unblocking() fcntl
calls around RECVFILE on the non-blocking socket.
Instead uses RECVFILE in a loop, and only drops
back to set_blocking()/set_unblocking() once
RECVFILE returns -1/EAGAIN/EWOULDBLOCK.

From the samba-technical list:

------------------------------------------------
The iometer 512b sequential write shows following result,
Before applying this patch: 75333 IOps
After applying this patch: 82691 IOps
------------------------------------------------

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

1 files changed, 43 insertions, 13 deletions

diff --git a/source3/smbd/vfs.c b/source3/smbd/vfs.c
index bc9157a8871..897bf1f338e 100644
--- a/source3/smbd/vfs.c
+++ b/source3/smbd/vfs.c
@@ -473,24 +473,54 @@ ssize_t vfs_pwrite_data(struct smb_request *req,
 
 	if (req && req->unread_bytes) {
 		int sockfd = req->sconn->sock;
-		int old_flags;
 		SMB_ASSERT(req->unread_bytes == N);
 		/* VFS_RECVFILE must drain the socket
 		 * before returning. */
 		req->unread_bytes = 0;
-		/* Ensure the socket is blocking. */
-		old_flags = fcntl(sockfd, F_GETFL, 0);
-		if (set_blocking(sockfd, true) == -1) {
-			return (ssize_t)-1;
-		}
-		ret = SMB_VFS_RECVFILE(sockfd,
-					fsp,
-					offset,
-					N);
-		if (fcntl(sockfd, F_SETFL, old_flags) == -1) {
-			return (ssize_t)-1;
+		/*
+		 * Leave the socket non-blocking and
+		 * use SMB_VFS_RECVFILE. If it returns
+		 * EAGAIN || EWOULDBLOCK temporarily set
+		 * the socket blocking and retry
+		 * the RECVFILE.
+		 */
+		while (total < N) {
+			ret = SMB_VFS_RECVFILE(sockfd,
+						fsp,
+						offset + total,
+						N - total);
+#if defined(EWOULDBLOCK)
+			if (ret == 0 || (ret == -1 &&
+				(errno == EAGAIN || errno == EWOULDBLOCK))) {
+#else /* EWOULDBLOCK */
+			if (ret == 0 || (ret == -1 && errno == EAGAIN)) {
+#endif /* EWOULDBLOCK */
+				int old_flags;
+				/* Ensure the socket is blocking. */
+				old_flags = fcntl(sockfd, F_GETFL, 0);
+				if (set_blocking(sockfd, true) == -1) {
+					return (ssize_t)-1;
+				}
+				ret = SMB_VFS_RECVFILE(sockfd,
+							fsp,
+							offset + total,
+							N - total);
+				if (fcntl(sockfd, F_SETFL, old_flags) == -1) {
+					return (ssize_t)-1;
+				}
+				if (ret == -1) {
+					return (ssize_t)-1;
+				}
+				total += ret;
+				return (ssize_t)total;
+			}
+			/* Any other error case. */
+			if (ret == -1) {
+				return ret;
+			}
+			total += ret;
 		}
-		return ret;
+		return (ssize_t)total;
 	}
 
 	while (total < N) {