Re: [Xen-devel] [PATCH 1/9] libxl: disks: Make LIBXL_DISK_BACKEND_UNKNOWN work

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [Xen-devel] [PATCH 1/9] libxl: disks: Make 
LIBXL_DISK_BACKEND_UNKNOWN work"):
> I think this should be treated the same as you did above, by adding an
> explicit fallback before the switch statement, for clarity.

OK.  This results in two copies of the same comment.  Really we should
have a common function for figuring out the correct backend, but this
at least makes things no worse.

Ian.


commit ee4720b0f9b15be152b10656b9b3e13b83be6c55
Author: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Date:   Fri May 6 09:02:02 2011 +0100

    libxl: disks: Make LIBXL_DISK_BACKEND_UNKNOWN work
    
    libxl callers should not be required to specify the backend if they
    don't want to.  So LIBXL_DISK_BACKEND_UNKNOWN should instruct libxl to
    choose the backend for itself.
    
    For now, we do this by simply treating it the same as BACKEND_TAP,
    which itself falls back to other methods.
    
    More thorough fixes for the disk handling will follow.
    
    Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index c21cfe7..a36de58 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -991,6 +991,21 @@ int libxl_device_disk_add(libxl_ctx *ctx, uint32_t domid, 
libxl_device_disk *dis
     device.domid = domid;
     device.kind = DEVICE_VBD;
 
+
+    /*
+     * Fixing the incoming backend type to try to decide on which
+     * backend to use.  Unfortunately at the moment this code is
+     * utterly broken, but it more or less works.
+     */
+
+    /*
+     * Backend type UNKNOWN should mean "caller does not want to specify",
+     * not "break pointlessely".  (Callers should not be required to
+     * specify the backend if they don't want to.)
+     */
+    if (disk->backend == LIBXL_DISK_BACKEND_UNKNOWN)
+        disk->backend = LIBXL_DISK_BACKEND_TAP;
+
     /* If blktap is not available then fallback to qdisk */
     if (disk->backend == LIBXL_DISK_BACKEND_TAP && !libxl__blktap_enabled(&gc))
         disk->backend = LIBXL_DISK_BACKEND_QDISK;
@@ -1126,6 +1141,20 @@ char * libxl_device_disk_local_attach(libxl_ctx *ctx, 
libxl_device_disk *disk)
     char *dev = NULL;
     char *ret = NULL;
 
+    /*
+     * Fixing the incoming backend type to try to decide on which
+     * backend to use.  Unfortunately at the moment this code is
+     * utterly broken, but it more or less works.
+     */
+
+    /*
+     * Backend type UNKNOWN should mean "caller does not want to specify",
+     * not "break pointlessely".  (Callers should not be required to
+     * specify the backend if they don't want to.)
+     */
+    if (disk->backend == LIBXL_DISK_BACKEND_UNKNOWN)
+        disk->backend = LIBXL_DISK_BACKEND_TAP;
+
     switch (disk->backend) {
         case LIBXL_DISK_BACKEND_PHY:
             if (disk->format != LIBXL_DISK_FORMAT_RAW) {
@@ -1175,7 +1204,6 @@ char * libxl_device_disk_local_attach(libxl_ctx *ctx, 
libxl_device_disk *disk)
                 disk->pdev_path);
             dev = disk->pdev_path;
             break;
-        case LIBXL_DISK_BACKEND_UNKNOWN:
         default:
             LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend "
                 "type: %d", disk->backend);

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel