[CRIU] [PATCH] criu restore: mismatched pid debug

[Kir Kolyshkin]

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Sometimes we fail to restore because of PID mismatch. In this case,
we would like to know who the hell has taken our PID. Let's print
a process tree, which looks something like this (this example is
obviously from the host):

1 /usr/lib/systemd/systemd --switched-root --system --deserialize 24
\_482 /usr/lib/systemd/systemd-journald
\_746 /sbin/auditd
  \_748 /sbin/audispd
    \_751 /usr/sbin/sedispatch
\_769 /usr/lib/systemd/systemd-logind

This is debug for https://github.com/xemul/criu/issues/282.

Signed-off-by: Kir Kolyshkin <kir at openvz.org>
---
 criu/cr-restore.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/criu/cr-restore.c b/criu/cr-restore.c
index e78b72e..91874c0 100644
--- a/criu/cr-restore.c
+++ b/criu/cr-restore.c
@@ -1323,6 +1323,50 @@ static int create_children_and_session(void)
        return 0;
 }

+static int show_pstree(pid_t p, int level)
+{
+       pid_t *ch;
+       int i, nr_ch, ret;
+       char cmd[80];
+       int fd, len, llen;
+
+       /* limit output to a single line on a terminal */
+       llen = 79 - printf("%*s%d ", level*2, level ? "\\_" : "", p);
+
+       fd = open_proc(p, "cmdline");
+       if (fd < 0)
+               return -1;
+       len = read(fd, cmd, sizeof(cmd) - 1);
+       close(fd);
+
+       if (len > 0) {
+               if (len > llen) {
+                       len = llen;
+                       // ellipsis
+                       cmd[len - 1] = '.';
+                       cmd[len - 2] = '.';
+               }
+               for (i = 0; i < len; i++)
+                       if (cmd[i] == '\0')
+                               cmd[i] = ' ';
+               cmd[len] = '\0';
+               puts(cmd);
+       } else {
+               puts("???");
+       }
+
+       ret = parse_children(p, &ch, &nr_ch);
+       if (ret < 0)
+               return ret;
+
+       for (i = 0; i < nr_ch; i++) {
+               show_pstree(ch[i], level+1);
+       }
+
+       xfree(ch);
+       return 0;
+}
+
 static int restore_task_with_children(void *_arg)
 {
        struct cr_clone_arg *ca = _arg;
@@ -1351,6 +1395,7 @@ static int restore_task_with_children(void *_arg)
        pid = getpid();
        if (vpid(current) != pid) {
                pr_err("Pid %d do not match expected %d\n", pid, vpid(current));
+               show_pstree(1, 0);
                set_task_cr_err(EEXIST);
                goto err;
        }
--
2.9.3