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authorJohannes Sixt <j6t@kdbg.org>2010-01-10 13:11:22 (GMT)
committerJunio C Hamano <gitster@pobox.com>2010-01-10 18:15:03 (GMT)
commit2b541bf8be2bbd6cc8daf8e3d5d4a8ee30b2ce4e (patch)
treea96beedf645609deb877c8b6180bae4df1fa658e /run-command.c
parentab0b41daf62ec3076e980fcad492b1997b35f22b (diff)
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start_command: detect execvp failures early
Previously, failures during execvp could be detected only by finish_command. However, in some situations it is beneficial for the parent process to know earlier that the child process will not run. The idea to use a pipe to signal failures to the parent process and the test case were lifted from patches by Ilari Liusvaara. Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'run-command.c')
-rw-r--r--run-command.c47
1 files changed, 46 insertions, 1 deletions
diff --git a/run-command.c b/run-command.c
index dccac37..efe9fe4 100644
--- a/run-command.c
+++ b/run-command.c
@@ -17,6 +17,12 @@ static inline void dup_devnull(int to)
#ifndef WIN32
static int child_err = 2;
+static int child_notifier = -1;
+
+static void notify_parent(void)
+{
+ write(child_notifier, "", 1);
+}
static NORETURN void die_child(const char *err, va_list params)
{
@@ -142,6 +148,11 @@ fail_pipe:
trace_argv_printf(cmd->argv, "trace: run_command:");
#ifndef WIN32
+{
+ int notify_pipe[2];
+ if (pipe(notify_pipe))
+ notify_pipe[0] = notify_pipe[1] = -1;
+
fflush(NULL);
cmd->pid = fork();
if (!cmd->pid) {
@@ -156,6 +167,11 @@ fail_pipe:
}
set_die_routine(die_child);
+ close(notify_pipe[0]);
+ set_cloexec(notify_pipe[1]);
+ child_notifier = notify_pipe[1];
+ atexit(notify_parent);
+
if (cmd->no_stdin)
dup_devnull(0);
else if (need_in) {
@@ -196,8 +212,16 @@ fail_pipe:
unsetenv(*cmd->env);
}
}
- if (cmd->preexec_cb)
+ if (cmd->preexec_cb) {
+ /*
+ * We cannot predict what the pre-exec callback does.
+ * Forgo parent notification.
+ */
+ close(child_notifier);
+ child_notifier = -1;
+
cmd->preexec_cb();
+ }
if (cmd->git_cmd) {
execv_git_cmd(cmd->argv);
} else {
@@ -215,6 +239,27 @@ fail_pipe:
if (cmd->pid < 0)
error("cannot fork() for %s: %s", cmd->argv[0],
strerror(failed_errno = errno));
+
+ /*
+ * Wait for child's execvp. If the execvp succeeds (or if fork()
+ * failed), EOF is seen immediately by the parent. Otherwise, the
+ * child process sends a single byte.
+ * Note that use of this infrastructure is completely advisory,
+ * therefore, we keep error checks minimal.
+ */
+ close(notify_pipe[1]);
+ if (read(notify_pipe[0], &notify_pipe[1], 1) == 1) {
+ /*
+ * At this point we know that fork() succeeded, but execvp()
+ * failed. Errors have been reported to our stderr.
+ */
+ wait_or_whine(cmd->pid, cmd->argv[0],
+ cmd->silent_exec_failure);
+ failed_errno = errno;
+ cmd->pid = -1;
+ }
+ close(notify_pipe[0]);
+}
#else
{
int s0 = -1, s1 = -1, s2 = -1; /* backups of stdin, stdout, stderr */