From 7236eb0dda54324c7d5909c8f01ef2aaaefb3e30 Mon Sep 17 00:00:00 2001
From: jilles <jilles@FreeBSD.org>
Date: Tue, 2 Apr 2013 21:34:38 +0000
Subject: [PATCH] sh: Write as much into the heredoc pipe as possible, to avoid
 forking.

Use non-blocking I/O to write as much as the pipe will accept (often 64K,
but it can be as little as 4K), avoiding the need for the ugly PIPESIZE
constant. If PIPESIZE was set too high, a deadlock would occur.
---
 bin/sh/redir.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/bin/sh/redir.c b/bin/sh/redir.c
index c11cb719e2d5..fda094d27d56 100644
--- a/bin/sh/redir.c
+++ b/bin/sh/redir.c
@@ -64,7 +64,6 @@ __FBSDID("$FreeBSD$");
 
 #define EMPTY -2		/* marks an unused slot in redirtab */
 #define CLOSED -1		/* fd was not open before redir */
-#define PIPESIZE 4096		/* amount of buffering in a pipe */
 
 
 MKINIT
@@ -253,7 +252,9 @@ openhere(union node *redir)
 {
 	char *p;
 	int pip[2];
-	int len = 0;
+	size_t len = 0;
+	int flags;
+	ssize_t written = 0;
 
 	if (pipe(pip) < 0)
 		error("Pipe call failed: %s", strerror(errno));
@@ -263,9 +264,16 @@ openhere(union node *redir)
 	else
 		p = redir->nhere.doc->narg.text;
 	len = strlen(p);
-	if (len <= PIPESIZE) {
-		xwrite(pip[1], p, len);
+	if (len == 0)
 		goto out;
+	flags = fcntl(pip[1], F_GETFL, 0);
+	if (flags != -1 && fcntl(pip[1], F_SETFL, flags | O_NONBLOCK) != -1) {
+		written = write(pip[1], p, len);
+		if (written < 0)
+			written = 0;
+		if ((size_t)written == len)
+			goto out;
+		fcntl(pip[1], F_SETFL, flags);
 	}
 
 	if (forkshell((struct job *)NULL, (union node *)NULL, FORK_NOJOB) == 0) {
@@ -275,7 +283,7 @@ openhere(union node *redir)
 		signal(SIGHUP, SIG_IGN);
 		signal(SIGTSTP, SIG_IGN);
 		signal(SIGPIPE, SIG_DFL);
-		xwrite(pip[1], p, len);
+		xwrite(pip[1], p + written, len - written);
 		_exit(0);
 	}
 out: