[PATCH] getroot: Correctly handle missing btrfs device identifiers.

[James Johnston]

>From 97bcb9eb8c34329a8ca1ec88fd89296e273ceb24 Mon Sep 17 00:00:00 2001
From: James Johnston <address@hidden>
Date: Thu, 17 Mar 2016 15:10:49 +0000
Subject: [PATCH] getroot: Correctly handle missing btrfs device identifiers.

The btrfs driver's BTRFS_IOC_FS_INFO ioctl only tells you the maximum
device ID and the number of devices.  It does not tell you which
device IDs may no longer be allocated - for example, if a device is
later deleted from the file system, its device ID won't be allocated
any more.

You must then probe each device ID with BTRFS_IOC_DEV_INFO to see if
it is a valid device or not.  It is not an error condition for this
ioctl to return ENODEV: it seems to mean that the device was deleted
by the user.

Signed-off-by: James Johnston <address@hidden>
---
 grub-core/osdep/linux/getroot.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/grub-core/osdep/linux/getroot.c b/grub-core/osdep/linux/getroot.c
index 10480b6..852f3a2 100644
--- a/grub-core/osdep/linux/getroot.c
+++ b/grub-core/osdep/linux/getroot.c
@@ -242,15 +242,29 @@ grub_find_root_devices_from_btrfs (const char *dir)
       struct btrfs_ioctl_dev_info_args devi;
       memset (&devi, 0, sizeof (devi));
       devi.devid = i;
+      /* We have to probe all possible device IDs, since btrfs doesn't
+        give us a list of all the valid ones.  */
       if (ioctl (fd, BTRFS_IOC_DEV_INFO, &devi) < 0)
        {
-         close (fd);
-         free (ret);
-         return NULL;
+         /* ENODEV is normal, e.g. if the first device is deleted from
+            an array. */
+         int last_error = errno;
+         if (last_error != ENODEV)
+           {
+             grub_util_warn(_("btrfs device info could not be read "
+                              "for %s, device %d: errno %d"), dir, i,
+                              last_error);
+             close (fd);
+             free (ret);
+             return NULL;
+           }
+       }
+      else
+       {
+         ret[j++] = xstrdup ((char *) devi.path);
+         if (j >= fsi.num_devices)
+           break;
        }
-      ret[j++] = xstrdup ((char *) devi.path);
-      if (j >= fsi.num_devices)
-       break;
     }
   close (fd);
   ret[j] = 0;
-- 
1.9.5.msysgit.1