[Qemu-devel] [PATCH v2 2/2] xen: dont try setting max grants multiple times

[Juergen Gross <jgross@suse.com>]

Trying to call xengnttab_set_max_grants() with the same file handle
might fail on some kernels, as this operation is allowed only once.

This is a problem for the qdisk backend as blk_connect() can be
called multiple times for a domain, e.g. in case grub-xen is being
used to boot it.

So instead of letting the generic backend code open the gnttab device
do it in blk_connect() and close it again in blk_disconnect.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- always call blk_disconnect() from blk_free() in order to have the
  gnttab device node closed (Anthony Perard)
---
 hw/block/xen_disk.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 62506e3167..e431bd89e8 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -1220,6 +1220,12 @@ static int blk_connect(struct XenDevice *xendev)
     /* Add on the number needed for the ring pages */
     max_grants += blkdev->nr_ring_ref;
 
+    blkdev->xendev.gnttabdev = xengnttab_open(NULL, 0);
+    if (blkdev->xendev.gnttabdev == NULL) {
+        xen_pv_printf(xendev, 0, "xengnttab_open failed: %s\n",
+                      strerror(errno));
+        return -1;
+    }
     if (xengnttab_set_max_grants(blkdev->xendev.gnttabdev, max_grants)) {
         xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
                       strerror(errno));
@@ -1327,6 +1333,11 @@ static void blk_disconnect(struct XenDevice *xendev)
         }
         blkdev->feature_persistent = false;
     }
+
+    if (blkdev->xendev.gnttabdev) {
+        xengnttab_close(blkdev->xendev.gnttabdev);
+        blkdev->xendev.gnttabdev = NULL;
+    }
 }
 
 static int blk_free(struct XenDevice *xendev)
@@ -1334,9 +1345,7 @@ static int blk_free(struct XenDevice *xendev)
     struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
     struct ioreq *ioreq;
 
-    if (blkdev->blk || blkdev->sring) {
-        blk_disconnect(xendev);
-    }
+    blk_disconnect(xendev);
 
     while (!QLIST_EMPTY(&blkdev->freelist)) {
         ioreq = QLIST_FIRST(&blkdev->freelist);
@@ -1363,7 +1372,6 @@ static void blk_event(struct XenDevice *xendev)
 
 struct XenDevOps xen_blkdev_ops = {
     .size       = sizeof(struct XenBlkDev),
-    .flags      = DEVOPS_FLAG_NEED_GNTDEV,
     .alloc      = blk_alloc,
     .init       = blk_init,
     .initialise    = blk_connect,
-- 
2.12.3