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Re: [Xen-devel] BUG 4.2.2: xl cd-insert corrupts xenstore state

George Dunlap writes ("Re: BUG 4.2.2: xl cd-insert corrupts xenstore state"):
> Turns out I already fixed this once!
> commit c3556e2a1aee3c9b7dda5d57e85e8867fff1b9da
> Author: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Commit: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Here's the backport, which was nearly trivial.

I'll push this to 4.2 staging unless someone objevts.


commit 1eea2f30f79a1af817fe32c9e01673da1f31dd5f
Author: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Date:   Wed May 1 16:56:54 2013 +0100

    libxl: Fix bug in libxl_cdrom_insert, make more robust against bad xenstore 
    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>
    (cherry picked from commit c3556e2a1aee3c9b7dda5d57e85e8867fff1b9da)
    Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index a6e9601..9f04e36 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2135,6 +2135,7 @@ int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t domid, 
libxl_device_disk *disk,
     libxl__device device;
     const char * path;
+    char * tmp;
     flexarray_t *insert = NULL;
@@ -2171,8 +2172,11 @@ int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t domid, 
libxl_device_disk *disk,
     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;
+        }
     if (i == num) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Virtual device not found");
@@ -2192,6 +2196,16 @@ int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t domid, 
libxl_device_disk *disk,
     if (rc) goto out;
     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", 
+    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(4, 1);
     flexarray_append_pair(insert, "type",

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