[Xen-changelog] [xen-unstable] libxl: Fix bug in libxl_cdrom_insert, make more robust against bad xenstore data

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User George Dunlap <george.dunlap@xxxxxxxxxxxxx>
# Date 1354025621 0
# Node ID 1c69c938f641a643e6ebfbdfc412e2c601e7032d
# Parent  17ffbe7cf645029a9c9e0c875ccd9424ec56ac62
libxl: Fix bug in libxl_cdrom_insert, make more robust against bad xenstore data

libxl_cdrom_insert was failing to initialize the backend type,
resulting in the wrong default backend.  The result was not only that
the CD was not inserted properly, but also that some improper xenstore
entries were created, causing further block commands to fail.

This patch fixes the bug by setting the disk backend type based on the
type of the existing device.

It also makes the system more robust by checking to see that it has
got a valid path before proceeding to write a partial xenstore entry.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---


diff -r 17ffbe7cf645 -r 1c69c938f641 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c       Tue Nov 27 14:13:40 2012 +0000
+++ b/tools/libxl/libxl.c       Tue Nov 27 14:13:41 2012 +0000
@@ -2354,6 +2354,7 @@ int libxl_cdrom_insert(libxl_ctx *ctx, u
 
     libxl__device device;
     const char * path;
+    char * tmp;
 
     flexarray_t *insert = NULL;
 
@@ -2384,8 +2385,11 @@ int libxl_cdrom_insert(libxl_ctx *ctx, u
     disks = libxl_device_disk_list(ctx, domid, &num);
     for (i = 0; i < num; i++) {
         if (disks[i].is_cdrom && !strcmp(disk->vdev, disks[i].vdev))
-            /* found */
+        {
+            /* Found.  Set backend type appropriately. */
+            disk->backend=disks[i].backend;
             break;
+        }
     }
     if (i == num) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Virtual device not found");
@@ -2411,6 +2415,17 @@ int libxl_cdrom_insert(libxl_ctx *ctx, u
 
     path = libxl__device_backend_path(gc, &device);
 
+    /* Sanity check: make sure the backend exists before writing here */
+    tmp = libxl__xs_read(gc, XBT_NULL, libxl__sprintf(gc, "%s/frontend", 
path));
+    if (!tmp)
+    {
+        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Internal error: %s does not exist",
+            libxl__sprintf(gc, "%s/frontend", path));
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+
     insert = flexarray_make(gc, 4, 1);
 
     flexarray_append_pair(insert, "type",

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