From 281720ec39d444ff9cd5ad281c6fcc401ea02cf8 Mon Sep 17 00:00:00 2001
From: Natanael Copa <ncopa@alpinelinux.org>
Date: Tue, 20 Apr 2021 17:05:40 +0200
Subject: [PATCH] abuild-fetch: aquire a second lock using flock(2)

It seems that POSIX record lock does not work across namespaces. Use a
second lock using flock.

see https://gitlab.alpinelinux.org/alpine/abuild/-/issues/10026
---
 abuild-fetch.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/abuild-fetch.c b/abuild-fetch.c
index 477c5fe..f7f0a08 100644
--- a/abuild-fetch.c
+++ b/abuild-fetch.c
@@ -23,6 +23,7 @@ THE SOFTWARE.
 */
 
 
+#include <sys/file.h>
 #include <sys/wait.h>
 
 #include <err.h>
@@ -90,6 +91,7 @@ static int aquire_lock(const char *lockfile)
 	if (lockfd < 0)
 		err(1, "%s", lockfile);
 
+	/* create NFS-safe lock */
 	if (fcntl(lockfd, F_SETLK, &fl) < 0) {
 		int i;
 		printf("Waiting for %s ...\n", lockfile);
@@ -102,11 +104,20 @@ static int aquire_lock(const char *lockfile)
 			sleep(1);
 		}
 	}
+
+	int r = flock(lockfd, LOCK_EX);
+	if (r == -1)
+		err(1, "flock: %s", lockfile);
+
 	return lockfd;
 }
 
 static void release_lock(int lockfd)
 {
+	int r = flock(lockfd, LOCK_UN);
+	if (r == -1)
+		err(1, "flock");
+
 	close(lockfd);
 }