From 269ab318ef92bd7a70e474df918c1f72d2a17a5a Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Wed, 5 Sep 2012 08:02:48 +0200
Subject: [PATCH] BUG/MEDIUM: workaround an eglibc bug which truncates the
 pidfiles when nbproc > 1

Thomas Heil reported that when using nbproc > 1, his pidfiles were
regularly truncated. The issue could be tracked down to the presence
of a call to lseek(pidfile, 0, SEEK_SET) just before the close() call
in the children, resulting in the file being truncated by the children
while the parent was feeding it. This unexpected lseek() is transparently
performed by fclose().

Since there is no way to have the file automatically closed during the
fork, the only solution is to bypass the libc and use open/write/close
instead of fprintf() and fclose().

The issue was observed on eglibc 2.15.
---
 src/haproxy.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/haproxy.c b/src/haproxy.c
index 4e7508030..7439a4c98 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -1148,8 +1148,8 @@ int main(int argc, char **argv)
 {
 	int err, retry;
 	struct rlimit limit;
-	FILE *pidfile = NULL;
 	char errmsg[100];
+	int pidfd = -1;
 
 	init(argc, argv);
 	signal_register_fct(SIGQUIT, dump, SIGQUIT);
@@ -1264,7 +1264,6 @@ int main(int argc, char **argv)
 
 	/* open log & pid files before the chroot */
 	if (global.mode & MODE_DAEMON && global.pidfile != NULL) {
-		int pidfd;
 		unlink(global.pidfile);
 		pidfd = open(global.pidfile, O_CREAT | O_WRONLY | O_TRUNC, 0644);
 		if (pidfd < 0) {
@@ -1274,7 +1273,6 @@ int main(int argc, char **argv)
 			protocol_unbind_all();
 			exit(1);
 		}
-		pidfile = fdopen(pidfd, "w");
 	}
 
 #ifdef CONFIG_HAP_CTTPROXY
@@ -1362,15 +1360,18 @@ int main(int argc, char **argv)
 			}
 			else if (ret == 0) /* child breaks here */
 				break;
-			if (pidfile != NULL) {
-				fprintf(pidfile, "%d\n", ret);
-				fflush(pidfile);
+			if (pidfd >= 0) {
+				char pidstr[100];
+				snprintf(pidstr, sizeof(pidstr), "%d\n", ret);
+				write(pidfd, pidstr, strlen(pidstr));
 			}
 			relative_pid++; /* each child will get a different one */
 		}
 		/* close the pidfile both in children and father */
-		if (pidfile != NULL)
-			fclose(pidfile);
+		if (pidfd >= 0) {
+			//lseek(pidfd, 0, SEEK_SET);  /* debug: emulate eglibc bug */
+			close(pidfd);
+		}
 
 		/* We won't ever use this anymore */
 		free(oldpids);        oldpids = NULL;