xen: add a global indicator for grant copy being available

The Xen qdisk backend needs to test whether grant copy operations is
available in the kernel. Unfortunately this collides with using
xengnttab_set_max_grants() on some kernels as this operation has to
be the first one after opening the gnttab device.

In order to solve this problem test for the availability of grant copy
in xen_be_init() opening the gnttab device just for that purpose and
closing it again afterwards. Advertise the availability via a global
flag and use that flag in the qdisk backend.

Signed-off-by: Juergen Gross <[email protected]>
Acked-by: Anthony PERARD <[email protected]>
Signed-off-by: Stefano Stabellini <[email protected]>

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 536e2ee735ef05f0a69534a75b2ab1750ff507f8..62506e3167b70850fe948a4916a6edd11473af64 100644 (file)
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -121,9 +121,6 @@ struct XenBlkDev {
     unsigned int        persistent_gnt_count;
     unsigned int        max_grants;
 
-    /* Grant copy */
-    gboolean            feature_grant_copy;
-
     /* qemu block driver */
     DriveInfo           *dinfo;
     BlockBackend        *blk;
@@ -616,7 +613,7 @@ static void qemu_aio_complete(void *opaque, int ret)
         return;
     }
 
-    if (ioreq->blkdev->feature_grant_copy) {
+    if (xen_feature_grant_copy) {
         switch (ioreq->req.operation) {
         case BLKIF_OP_READ:
             /* in case of failure ioreq->aio_errors is increased */
@@ -638,7 +635,7 @@ static void qemu_aio_complete(void *opaque, int ret)
     }
 
     ioreq->status = ioreq->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
-    if (!ioreq->blkdev->feature_grant_copy) {
+    if (!xen_feature_grant_copy) {
         ioreq_unmap(ioreq);
     }
     ioreq_finish(ioreq);
@@ -698,7 +695,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
 {
     struct XenBlkDev *blkdev = ioreq->blkdev;
 
-    if (ioreq->blkdev->feature_grant_copy) {
+    if (xen_feature_grant_copy) {
         ioreq_init_copy_buffers(ioreq);
         if (ioreq->req.nr_segments && (ioreq->req.operation == BLKIF_OP_WRITE ||
             ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
@@ -750,7 +747,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
     }
     default:
         /* unknown operation (shouldn't happen -- parse catches this) */
-        if (!ioreq->blkdev->feature_grant_copy) {
+        if (!xen_feature_grant_copy) {
             ioreq_unmap(ioreq);
         }
         goto err;
@@ -1010,18 +1007,15 @@ static int blk_init(struct XenDevice *xendev)
 
     blkdev->file_blk  = BLOCK_SIZE;
 
-    blkdev->feature_grant_copy =
-                (xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);
-
     xen_pv_printf(&blkdev->xendev, 3, "grant copy operation %s\n",
-                  blkdev->feature_grant_copy ? "enabled" : "disabled");
+                  xen_feature_grant_copy ? "enabled" : "disabled");
 
     /* fill info
      * blk_connect supplies sector-size and sectors
      */
     xenstore_write_be_int(&blkdev->xendev, "feature-flush-cache", 1);
     xenstore_write_be_int(&blkdev->xendev, "feature-persistent",
-                          !blkdev->feature_grant_copy);
+                          !xen_feature_grant_copy);
     xenstore_write_be_int(&blkdev->xendev, "info", info);
 
     xenstore_write_be_int(&blkdev->xendev, "max-ring-page-order",

diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index c46cbb07594c495087534ee3be2784719672d0cb..0f849a26d28f25fddd58c5cab3c3c06d82ccac74 100644 (file)
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -44,6 +44,7 @@ BusState *xen_sysbus;
 /* public */
 struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
+bool xen_feature_grant_copy;
 
 /* private */
 static int debug;
@@ -519,6 +520,8 @@ void xenstore_update_fe(char *watch, struct XenDevice *xendev)
 
 int xen_be_init(void)
 {
+    xengnttab_handle *gnttabdev;
+
     xenstore = xs_daemon_open();
     if (!xenstore) {
         xen_pv_printf(NULL, 0, "can't connect to xenstored\n");
@@ -532,6 +535,14 @@ int xen_be_init(void)
         goto err;
     }
 
+    gnttabdev = xengnttab_open(NULL, 0);
+    if (gnttabdev != NULL) {
+        if (xengnttab_grant_copy(gnttabdev, 0, NULL) == 0) {
+            xen_feature_grant_copy = true;
+        }
+        xengnttab_close(gnttabdev);
+    }
+
     xen_sysdev = qdev_create(NULL, TYPE_XENSYSDEV);
     qdev_init_nofail(xen_sysdev);
     xen_sysbus = qbus_create(TYPE_XENSYSBUS, DEVICE(xen_sysdev), "xen-sysbus");

diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
index 8a6fbcbe20d33164a3b9343f4b9ed6321f450ab3..3a27692407979af5a22667d319b5cad518d6b6a7 100644 (file)
--- a/include/hw/xen/xen_backend.h
+++ b/include/hw/xen/xen_backend.h
@@ -16,6 +16,7 @@
 /* variables */
 extern struct xs_handle *xenstore;
 extern const char *xen_protocol;
+extern bool xen_feature_grant_copy;
 extern DeviceState *xen_sysdev;
 extern BusState *xen_sysbus;