[libvirt] [PATCH] [RFC] libxl: add discard support to libxl_device_disk

[Olaf Hering]

Translate libvirt discard settings into libxl-4.5 discard settings.
It makes use of upcoming changes for xen-4.5:
http://lists.xenproject.org/archives/html/xen-devel/2014-01/msg02632.html

This patch is not compile tested. How is a config file supposed to look
like to make use of a discard=on|off flag for a given disk image?

Signed-off-by: Olaf Hering <olaf at aepfle.de>
Cc: Jim Fehlig <jfehlig at suse.com>
---
 src/libxl/libxl_conf.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
index 4cefadf..8fc5e75 100644
--- a/src/libxl/libxl_conf.c
+++ b/src/libxl/libxl_conf.c
@@ -707,6 +707,26 @@ error:
     return -1;
 }
 
+static void
+libxlDiskSetDiscard(libxl_device_disk *x_disk, int discard)
+{
+    if (!x_disk->readwrite)
+        return;
+#if defined(LIBXL_HAVE_LIBXL_DEVICE_DISK_DISCARD_ENABLE)
+    /* libxl 4.5 */
+    switch (discard) {
+    case VIR_DOMAIN_DISK_DISCARD_DEFAULT:
+    case VIR_DOMAIN_DISK_DISCARD_UNMAP:
+        x_disk->discard_enable = 1;
+        break;
+    default:
+    case VIR_DOMAIN_DISK_DISCARD_IGNORE:
+        x_disk->discard_enable = 0;
+        break;
+    }
+#endif
+}
+
 int
 libxlMakeDisk(virDomainDiskDefPtr l_disk, libxl_device_disk *x_disk)
 {
@@ -817,6 +837,7 @@ libxlMakeDisk(virDomainDiskDefPtr l_disk, libxl_device_disk *x_disk)
     x_disk->removable = 1;
     x_disk->readwrite = !l_disk->readonly;
     x_disk->is_cdrom = l_disk->device == VIR_DOMAIN_DISK_DEVICE_CDROM ? 1 : 0;
+    libxlDiskSetDiscard(x_disk, l_disk->discard);
     if (l_disk->transient) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("libxenlight does not support transient disks"));