Check for IO errors after running a command

This is trying to implement the strict IO error checks that Jim Meyering
suggested, but explicitly limits it to just regular files. If a pipe gets
closed on us, we shouldn't complain about it.

If the subcommand already returned an error, that takes precedence (and we
assume that the subcommand already printed out any relevant messages
relating to it)

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -224,6 +224,8 @@ struct cmd_struct {
 
 static int run_command(struct cmd_struct *p, int argc, const char **argv)
 {
+	int status;
+	struct stat st;
 	const char *prefix;
 
 	prefix = NULL;
@@ -237,7 +239,24 @@ static int run_command(struct cmd_struct *p, int argc, const char **argv)
 	}
 	trace_argv_printf(argv, argc, "trace: built-in: git");
 
-	return p->fn(argc, argv, prefix);
+	status = p->fn(argc, argv, prefix);
+	if (status)
+		return status;
+
+	/* Somebody closed stdout? */
+	if (fstat(fileno(stdout), &st))
+		return 0;
+	/* Ignore write errors for pipes and sockets.. */
+	if (S_ISFIFO(st.st_mode) || S_ISSOCK(st.st_mode))
+		return 0;
+
+	/* Check for ENOSPC and EIO errors.. */
+	if (ferror(stdout))
+		die("write failure on standard output");
+	if (fflush(stdout) || fclose(stdout))
+		die("write failure on standard output: %s", strerror(errno));
+
+	return 0;
 }
 
 static void handle_internal_command(int argc, const char **argv)