cgroups: send two fds to attach to unified cgroup

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/cgroups/cgfsng.c b/src/lxc/cgroups/cgfsng.c
index 6e32704cdd2543b58d33119771464f46ee6cd995..564400221faedd324ede1c2079e4e8777eef38d0 100644 (file)
--- a/src/lxc/cgroups/cgfsng.c
+++ b/src/lxc/cgroups/cgfsng.c
@@ -2127,9 +2127,8 @@ static int cgroup_attach_leaf(const struct lxc_conf *conf, int unified_fd, pid_t
 static int cgroup_attach_create_leaf(const struct lxc_conf *conf,
                                     int unified_fd, int *sk_fd)
 {
-       __do_close int sk = *sk_fd;
-       int target_fds[2] = {-EBADF, -EBADF};
-       __do_close int target_fd1 = target_fds[0], target_fd2 = target_fds[1];
+       __do_close int sk = *sk_fd, target_fd0 = -EBADF, target_fd1 = -EBADF;
+       int target_fds[2];
        ssize_t ret;
 
        /* Create leaf cgroup. */
@@ -2137,28 +2136,29 @@ static int cgroup_attach_create_leaf(const struct lxc_conf *conf,
        if (ret < 0 && errno != EEXIST)
                return log_error_errno(-1, errno, "Failed to create leaf cgroup \".lxc\"");
 
-       target_fd1 = openat(unified_fd, ".lxc/cgroup.procs", O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
-       if (target_fd1 < 0)
+       target_fd0 = openat(unified_fd, ".lxc/cgroup.procs", O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
+       if (target_fd0 < 0)
                return log_error_errno(-errno, errno, "Failed to open \".lxc/cgroup.procs\"");
+       target_fds[0] = target_fd0;
 
-       target_fd2 = openat(unified_fd, "cgroup.procs", O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
-       if (target_fd2 < 0)
+       target_fd1 = openat(unified_fd, "cgroup.procs", O_WRONLY | O_CLOEXEC | O_NOFOLLOW);
+       if (target_fd1 < 0)
                return log_error_errno(-errno, errno, "Failed to open \".lxc/cgroup.procs\"");
+       target_fds[1] = target_fd1;
 
        ret = lxc_abstract_unix_send_fds(sk, target_fds, 2, NULL, 0);
        if (ret <= 0)
                return log_error_errno(-errno, errno, "Failed to send \".lxc/cgroup.procs\" fds %d and %d",
-                                      target_fd1, target_fd2);
+                                      target_fd0, target_fd1);
 
-       return log_debug(0, "Sent target cgroup fds %d and %d", target_fd1, target_fd2);
+       return log_debug(0, "Sent target cgroup fds %d and %d", target_fd0, target_fd1);
 }
 
 static int cgroup_attach_move_into_leaf(const struct lxc_conf *conf,
                                        int *sk_fd, pid_t pid)
 {
-       __do_close int sk = *sk_fd;
-       int target_fds[2] = {-EBADF, -EBADF};
-       __do_close int target_fd1 = target_fds[0], target_fd2 = target_fds[1];
+       __do_close int sk = *sk_fd, target_fd0 = -EBADF, target_fd1 = -EBADF;
+       int target_fds[2];
        char pidstr[INTTYPE_TO_STRLEN(int64_t) + 1];
        size_t pidstr_len;
        ssize_t ret;
@@ -2166,16 +2166,21 @@ static int cgroup_attach_move_into_leaf(const struct lxc_conf *conf,
        ret = lxc_abstract_unix_recv_fds(sk, target_fds, 2, NULL, 0);
        if (ret <= 0)
                return log_error_errno(-1, errno, "Failed to receive target cgroup fd");
+       target_fd0 = target_fds[0];
+       target_fd1 = target_fds[1];
 
        pidstr_len = sprintf(pidstr, INT64_FMT, (int64_t)pid);
 
+       ret = lxc_write_nointr(target_fd0, pidstr, pidstr_len);
+       if (ret > 0 && ret == pidstr_len)
+               return log_debug(0, "Moved process into target cgroup via fd %d", target_fd0);
+
        ret = lxc_write_nointr(target_fd1, pidstr, pidstr_len);
-       if (ret != pidstr_len && errno == EBUSY)
-               ret = lxc_write_nointr(target_fd2, pidstr, pidstr_len);
-       if (ret != pidstr_len)
-               return log_error_errno(-1, errno, "Failed to move process into target cgroup");
+       if (ret > 0 && ret == pidstr_len)
+               return log_debug(0, "Moved process into target cgroup via fd %d", target_fd1);
 
-       return log_debug(0, "Moved process into target cgroup");
+       return log_debug_errno(-1, errno, "Failed to move process into target cgroup via fd %d and %d",
+                              target_fd0, target_fd1);
 }
 
 struct userns_exec_unified_attach_data {