From 3530cf2bc933e0fc6a035026934af8976542bfff Mon Sep 17 00:00:00 2001
From: Richard Yao <richard.yao@clusterhq.com>
Date: Wed, 11 Mar 2015 14:24:46 -0400
Subject: [PATCH] Increase Linux pipe buffer size on zfs recv to the maximum
 system size

I noticed when reviewing documentation that it is possible for userspace
to use fctnl(fd, F_SETPIPE_SZ, (unsigned long) size) to change the
kernel pipe buffer size on Linux to increase the pipe size up to the
value specified in /proc/sys/fs/pipe-max-size. There are users using
mbuffer to improve zfs recv performance when piping over the network, so
it seems advantageous to integrate such functionality directly into the
zfs recv tool. This avoids the addition of two buffers and two copies
(one for the buffer mbuffer adds and another for the additional pipe),
so it should be more efficient. This could have been made configurable
and/or this could have changed the value back to the original after we
were done with the file descriptor, but I do not see a strong case for
doing either, so I went with a simple implementation.

Closes zfsonlinux/zfs#1161

Signed-off-by: Richard Yao <ryao@gentoo.org>
---
 lib/libzfs/libzfs_sendrecv.c | 39 ++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/lib/libzfs/libzfs_sendrecv.c b/lib/libzfs/libzfs_sendrecv.c
index e3572914c997..eb6f79203aa7 100644
--- a/lib/libzfs/libzfs_sendrecv.c
+++ b/lib/libzfs/libzfs_sendrecv.c
@@ -43,6 +43,7 @@
 #include <sys/mnttab.h>
 #include <sys/avl.h>
 #include <sys/debug.h>
+#include <sys/stat.h>
 #include <stddef.h>
 #include <pthread.h>
 #include <umem.h>
@@ -3297,6 +3298,44 @@ zfs_receive(libzfs_handle_t *hdl, const char *tosnap, recvflags_t *flags,
 	int err;
 	int cleanup_fd;
 	uint64_t action_handle = 0;
+#ifdef __linux__
+	struct stat sb;
+
+#ifndef F_SETPIPE_SZ
+#define	F_SETPIPE_SZ (F_SETLEASE + 7)
+#endif
+
+#ifndef F_GETPIPE_SZ
+#define	F_GETPIPE_SZ (F_GETLEASE + 7)
+#endif
+
+	if (fstat(infd, &sb) == -1) {
+		perror("fstat");
+		return (-2);
+	}
+
+	/*
+	 * It is not uncommon for gigabytes to be processed in zfs receive.
+	 * Speculatively increase the buffer size via Linux-specific fcntl()
+	 * call.
+	 */
+	if (S_ISFIFO(sb.st_mode)) {
+		FILE *procf = fopen("/proc/sys/fs/pipe-max-size", "r");
+
+		if (procf != NULL) {
+			unsigned long pipe_max_size;
+			unsigned long pipe_current_size;
+			if (fscanf(procf, "%lu", &pipe_max_size) > 0) {
+				pipe_current_size = fcntl(infd, F_GETPIPE_SZ);
+				if (pipe_current_size > 0 &&
+				    pipe_max_size > pipe_current_size)
+					(void) fcntl(infd, F_SETPIPE_SZ,
+					    pipe_max_size);
+			}
+			fclose(procf);
+		}
+	}
+#endif
 
 	cleanup_fd = open(ZFS_DEV, O_RDWR);
 	VERIFY(cleanup_fd >= 0);