[Bug 1136542] [NEW] g_unix_mount_points_get() won't work in a LXC container unless /etc/fstab is set

[Matt Fischer]

Public bug reported:

Seen on several versions of glib2 and Ubuntu:
12.10 - amd64
libglib2.0-0:amd64          2.34.1-1ubuntu1

12.04 armhf
libglib2.0-0          2.32.3-0ubuntu1

g_unix_mount_points_get() returns an empty list when run inside an LXC
container. I think this is because it reads /etc/fstab to gather mount
info instead of reading /proc/mounts. This means that for LXC
containers, it will fail using a default container, returning no mount
points. There are other cases where fstab is neither complete up to date
or accurate and I think that reading mounts would make more sense. Below
is a repro case.

/* gcc -g -ggdb -o dt dt.c `pkg-config --cflags --libs glib-2.0
libgtop-2.0 gio-2.0 gio-unix-2.0` */

/* g_unix_mount_points_get() - returns empty set inside a container */

#include <glib.h>
#include <gio/gio.h>
#include <gio/gunixmounts.h>
#include <stdio.h>
#include <stdlib.h>

int main(void) {
  GList        *points;
  GList        *p;
  points = g_unix_mount_points_get (NULL);
  if (points == NULL) {
      printf("no mounts found!");
  }
  for (p = points; p != NULL; p = p->next)
    {
      GUnixMountEntry *mount = p->data;
      const char *mount_path;

      mount_path = g_unix_mount_get_mount_path (mount);
      printf("Found a mount: %s\n", mount_path);
    }
  g_list_free (points);
}

** Affects: glib2.0 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1136542

Title:
  g_unix_mount_points_get() won't work in a LXC container unless
  /etc/fstab is set

Status in “glib2.0” package in Ubuntu:
  New

Bug description:
  Seen on several versions of glib2 and Ubuntu:
  12.10 - amd64
  libglib2.0-0:amd64          2.34.1-1ubuntu1

  12.04 armhf
  libglib2.0-0          2.32.3-0ubuntu1

  g_unix_mount_points_get() returns an empty list when run inside an LXC
  container. I think this is because it reads /etc/fstab to gather mount
  info instead of reading /proc/mounts. This means that for LXC
  containers, it will fail using a default container, returning no mount
  points. There are other cases where fstab is neither complete up to
  date or accurate and I think that reading mounts would make more
  sense. Below is a repro case.

  /* gcc -g -ggdb -o dt dt.c `pkg-config --cflags --libs glib-2.0
  libgtop-2.0 gio-2.0 gio-unix-2.0` */

  /* g_unix_mount_points_get() - returns empty set inside a container */

  #include <glib.h>
  #include <gio/gio.h>
  #include <gio/gunixmounts.h>
  #include <stdio.h>
  #include <stdlib.h>

  int main(void) {
    GList        *points;
    GList        *p;
    points = g_unix_mount_points_get (NULL);
    if (points == NULL) {
        printf("no mounts found!");
    }
    for (p = points; p != NULL; p = p->next)
      {
        GUnixMountEntry *mount = p->data;
        const char *mount_path;

        mount_path = g_unix_mount_get_mount_path (mount);
        printf("Found a mount: %s\n", mount_path);
      }
    g_list_free (points);
  }

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