start: open /dev/null from "host" /dev

Sometimes, a container doesn't have /dev/null.
For example, I have this problem with Android container.

This fixes #910 (github) for me.

Signed-off-by: Aleksandr Mezin <mezin.alexander@gmail.com>

diff --git a/src/lxc/start.c b/src/lxc/start.c
index bb7009ba87170d723e6c318bf6cf601bfc9d4308..fc98eb396493744c38c9e8bc0667c737fe8f9df1 100644 (file)
--- a/src/lxc/start.c
+++ b/src/lxc/start.c
@@ -710,6 +710,7 @@ static int do_start(void *data)
 {
        struct lxc_list *iterator;
        struct lxc_handler *handler = data;
+       int devnull_fd = -1;
 
        if (sigprocmask(SIG_SETMASK, &handler->oldmask, NULL)) {
                SYSERROR("failed to set sigprocmask");
@@ -788,6 +789,13 @@ static int do_start(void *data)
        }
        #endif
 
+       if (handler->backgrounded) {
+               devnull_fd = open_devnull();
+
+               if (devnull_fd < 0)
+                       goto out_warn_father;
+       }
+
        /* Setup the container, ip, names, utsname, ... */
        if (lxc_setup(handler)) {
                ERROR("failed to setup the container");
@@ -796,7 +804,7 @@ static int do_start(void *data)
 
        /* ask father to setup cgroups and wait for him to finish */
        if (lxc_sync_barrier_parent(handler, LXC_SYNC_CGROUP))
-               return -1;
+               goto out_error;
 
        /* Set the label to change to when we exec(2) the container's init */
        if (lsm_process_label_set(NULL, handler->conf, 1, 1) < 0)
@@ -853,9 +861,14 @@ static int do_start(void *data)
 
        close(handler->sigfd);
 
-       if (handler->backgrounded && null_stdfds() < 0)
+       if (handler->backgrounded && set_stdfds(devnull_fd))
                goto out_warn_father;
 
+       if (devnull_fd >= 0) {
+               close(devnull_fd);
+               devnull_fd = -1;
+       }
+
        if (cgns_supported() && unshare(CLONE_NEWCGROUP) != 0) {
                SYSERROR("Failed to unshare cgroup namespace");
                goto out_warn_father;
@@ -871,6 +884,11 @@ out_warn_father:
        /* we want the parent to know something went wrong, so we return a special
         * error code. */
        lxc_sync_wake_parent(handler, LXC_SYNC_ERROR);
+
+out_error:
+       if (devnull_fd >= 0)
+               close(devnull_fd);
+
        return -1;
 }