[PATCH] detect dup failure

[Jim Meyering <jim@meyering.net>]

Without this, if you ever run out of file descriptors, dup will
fail (silently), fdopen will return NULL, and fprintf will
try to dereference NULL (i.e., usually segfault).

Signed-off-by: Jim Meyering <jim@meyering.net>
---
 builtin-log.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/builtin-log.c b/builtin-log.c
index 073a2a1..ca54387 100644
--- a/builtin-log.c
+++ b/builtin-log.c
@@ -588,8 +588,12 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (ignore_if_in_upstream)
 		get_patch_ids(&rev, &ids, prefix);

-	if (!use_stdout)
-		realstdout = fdopen(dup(1), "w");
+	if (!use_stdout) {
+		int fd = dup(1);
+		if (fd < 0)
+			die("failed to duplicate standard output");
+		realstdout = fdopen(fd, "w");
+	}

 	prepare_revision_walk(&rev);
 	while ((commit = get_revision(&rev)) != NULL) {