start_command: detect execvp failures early

diff --git a/run-command.c b/run-command.c
index 02c7bfba8fb7491b936d819cd54054e645b58ef8..efe9fe413887966ced2bb3cd976789ec8789ec4d 100644 (file)
--- 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)
 {
@@ -39,6 +45,48 @@ static inline void set_cloexec(int fd)
 }
 #endif
 
+static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
+{
+       int status, code = -1;
+       pid_t waiting;
+       int failed_errno = 0;
+
+       while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
+               ;       /* nothing */
+
+       if (waiting < 0) {
+               failed_errno = errno;
+               error("waitpid for %s failed: %s", argv0, strerror(errno));
+       } else if (waiting != pid) {
+               error("waitpid is confused (%s)", argv0);
+       } else if (WIFSIGNALED(status)) {
+               code = WTERMSIG(status);
+               error("%s died of signal %d", argv0, code);
+               /*
+                * This return value is chosen so that code & 0xff
+                * mimics the exit code that a POSIX shell would report for
+                * a program that died from this signal.
+                */
+               code -= 128;
+       } else if (WIFEXITED(status)) {
+               code = WEXITSTATUS(status);
+               /*
+                * Convert special exit code when execvp failed.
+                */
+               if (code == 127) {
+                       code = -1;
+                       failed_errno = ENOENT;
+                       if (!silent_exec_failure)
+                               error("cannot run %s: %s", argv0,
+                                       strerror(ENOENT));
+               }
+       } else {
+               error("waitpid is confused (%s)", argv0);
+       }
+       errno = failed_errno;
+       return code;
+}
+
 int start_command(struct child_process *cmd)
 {
        int need_in, need_out, need_err;
@@ -100,6 +148,11 @@ int start_command(struct child_process *cmd)
        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) {
@@ -114,6 +167,11 @@ int start_command(struct child_process *cmd)
                }
                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) {
@@ -154,8 +212,16 @@ int start_command(struct child_process *cmd)
                                        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 {
@@ -173,6 +239,27 @@ int start_command(struct child_process *cmd)
        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 */
@@ -272,48 +359,6 @@ int start_command(struct child_process *cmd)
        return 0;
 }
 
-static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
-{
-       int status, code = -1;
-       pid_t waiting;
-       int failed_errno = 0;
-
-       while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
-               ;       /* nothing */
-
-       if (waiting < 0) {
-               failed_errno = errno;
-               error("waitpid for %s failed: %s", argv0, strerror(errno));
-       } else if (waiting != pid) {
-               error("waitpid is confused (%s)", argv0);
-       } else if (WIFSIGNALED(status)) {
-               code = WTERMSIG(status);
-               error("%s died of signal %d", argv0, code);
-               /*
-                * This return value is chosen so that code & 0xff
-                * mimics the exit code that a POSIX shell would report for
-                * a program that died from this signal.
-                */
-               code -= 128;
-       } else if (WIFEXITED(status)) {
-               code = WEXITSTATUS(status);
-               /*
-                * Convert special exit code when execvp failed.
-                */
-               if (code == 127) {
-                       code = -1;
-                       failed_errno = ENOENT;
-                       if (!silent_exec_failure)
-                               error("cannot run %s: %s", argv0,
-                                       strerror(ENOENT));
-               }
-       } else {
-               error("waitpid is confused (%s)", argv0);
-       }
-       errno = failed_errno;
-       return code;
-}
-
 int finish_command(struct child_process *cmd)
 {
        return wait_or_whine(cmd->pid, cmd->argv[0], cmd->silent_exec_failure);