Fix endless loop when mpd is launched from a non-interactive shell.

Thanks to _noth_ for the patch, this fixes Mantis bug #1534

_noth_ wrote:
> When MPD is launched from a non-interactive shell, it enters an endless
> loop, filling up its error log file with "error accept()'ing" messages.
> This is caused by the fact that stdin is already closed when mpd starts
> up.  listenOnPort() opens up the first of its sockets as fd 0 (the first
> empty fd table position). Then, setup_log_output()->redirect_stdin()
> overwrites fd0 (fd=open("/dev/null",...); dup2(fd, STDIN_FILENO);)
> without checking if it corresponds to the actual standard input (or if
> it is open in the first place).  This means that listenSockets[0].fd now
> is a fd for /dev/null, thus doIOForInterfaces()->getConnections() can't
> accept(2) on it and fails with the above error. The attached patch fixes
> this for me.

r6843 in trunk

git-svn-id: https://svn.musicpd.org/mpd/branches/branch-0.13.0-fixes@7159 09075e82-0dd4-0310-85a5-a0d7c8717e4f

1 files changed, 5 insertions, 1 deletions

diff --git a/src/log.c b/src/log.c
index fa4ae64f0..974c07146 100644
--- a/src/log.c
+++ b/src/log.c
@@ -40,7 +40,11 @@ static const char *err_filename;
 /* redirect stdin to /dev/null to work around a libao bug */
 static void redirect_stdin(void)
 {
-	int fd;
+	int fd, st;
+	struct stat ss;
+
+	if ((st = fstat(STDIN_FILENO, &ss)) < 0 || ! isatty(STDIN_FILENO))
+		return;
 	if ((fd = open("/dev/null", O_RDONLY)) < 0)
 		FATAL("failed to open /dev/null %s\n", strerror(errno));
 	if (dup2(fd, STDIN_FILENO) < 0)