bindings: record mount namespace

This will allows us to attach to the mount namespace in case we need to debug or
perform some action on update.

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

diff --git a/bindings.c b/bindings.c
index fe521a3317625bb0e7afddc935ed399f8368ad74..885eb64936c9921653f5a66d0d44204698bfedbf 100644 (file)
--- a/bindings.c
+++ b/bindings.c
@@ -139,6 +139,7 @@ static char **hierarchies;
  * another namespace using the *at() family of functions
  * {openat(), fchownat(), ...}. */
 static int *fd_hierarchies;
+static int cgroup_mount_ns_fd = -1;
 
 static void unlock_mutex(pthread_mutex_t *l)
 {
@@ -421,6 +422,7 @@ static void print_subsystems(void)
 {
        int i;
 
+       fprintf(stderr, "mount namespace: %d\n", cgroup_mount_ns_fd);
        fprintf(stderr, "hierarchies:\n");
        for (i = 0; i < num_hierarchies; i++) {
                if (hierarchies[i])
@@ -4477,6 +4479,19 @@ static bool permute_root(void)
        return true;
 }
 
+static int preserve_mnt_ns(int pid)
+{
+       int ret;
+       size_t len = sizeof("/proc/") + 21 + sizeof("/ns/mnt");
+       char path[len];
+
+       ret = snprintf(path, len, "/proc/%d/ns/mnt", pid);
+       if (ret < 0 || (size_t)ret >= len)
+               return -1;
+
+       return open(path, O_RDONLY | O_CLOEXEC);
+}
+
 static bool cgfs_prepare_mounts(void)
 {
        if (!mkdir_p(BASEDIR, 0700)) {
@@ -4494,6 +4509,12 @@ static bool cgfs_prepare_mounts(void)
                return false;
        }
 
+       cgroup_mount_ns_fd = preserve_mnt_ns(getpid());
+       if (cgroup_mount_ns_fd < 0) {
+               lxcfs_error("Failed to preserve mount namespace: %s.\n", strerror(errno));
+               return false;
+       }
+
        if (mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0) < 0) {
                lxcfs_error("Failed to remount / private: %s.\n", strerror(errno));
                return false;
@@ -4567,19 +4588,6 @@ static bool cgfs_setup_controllers(void)
        return true;
 }
 
-static int preserve_ns(int pid)
-{
-       int ret;
-       size_t len = 5 /* /proc */ + 21 /* /int_as_str */ + 7 /* /ns/mnt */ + 1 /* \0 */;
-       char path[len];
-
-       ret = snprintf(path, len, "/proc/%d/ns/mnt", pid);
-       if (ret < 0 || (size_t)ret >= len)
-               return -1;
-
-       return open(path, O_RDONLY | O_CLOEXEC);
-}
-
 static void __attribute__((constructor)) collect_and_mount_subsystems(void)
 {
        FILE *f;
@@ -4623,7 +4631,7 @@ static void __attribute__((constructor)) collect_and_mount_subsystems(void)
        }
 
        /* Preserve initial namespace. */
-       init_ns = preserve_ns(getpid());
+       init_ns = preserve_mnt_ns(getpid());
        if (init_ns < 0) {
                lxcfs_error("%s\n", "Failed to preserve initial mount namespace.");
                goto out;
@@ -4680,4 +4688,7 @@ static void __attribute__((destructor)) free_subsystems(void)
        }
        free(hierarchies);
        free(fd_hierarchies);
+
+       if (cgroup_mount_ns_fd >= 0)
+               close(cgroup_mount_ns_fd);
 }