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start_command: detect execvp failures early

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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>
This commit is contained in:
Johannes Sixt
2010-01-10 14:11:22 +01:00
committed by Junio C Hamano
parent ab0b41daf6
commit 2b541bf8be
4 changed files with 96 additions and 1 deletions
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47
run-command.c
View File

@ -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 */