xen_backend: add grant table helpers

This patch adds grant table helper functions to the xen_backend code to
localize error reporting and use of xen_domid.

The patch also defers the call to xengnttab_open() until just before the
initialise method in XenDevOps is invoked. This method is responsible for
mapping the shared ring. No prior method requires access to the grant table.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

2 files changed, 144 insertions, 12 deletions

diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index 7445b506ac..50412d6a09 100644
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -106,6 +106,103 @@ int xen_be_set_state(struct XenDevice *xendev, enum xenbus_state state)
     return 0;
 }
 
+void xen_be_set_max_grant_refs(struct XenDevice *xendev,
+                               unsigned int nr_refs)
+{
+    assert(xendev->ops->flags & DEVOPS_FLAG_NEED_GNTDEV);
+
+    if (xengnttab_set_max_grants(xendev->gnttabdev, nr_refs)) {
+        xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
+                      strerror(errno));
+    }
+}
+
+void *xen_be_map_grant_refs(struct XenDevice *xendev, uint32_t *refs,
+                            unsigned int nr_refs, int prot)
+{
+    void *ptr;
+
+    assert(xendev->ops->flags & DEVOPS_FLAG_NEED_GNTDEV);
+
+    ptr = xengnttab_map_domain_grant_refs(xendev->gnttabdev, nr_refs,
+                                          xen_domid, refs, prot);
+    if (!ptr) {
+        xen_pv_printf(xendev, 0,
+                      "xengnttab_map_domain_grant_refs failed: %s\n",
+                      strerror(errno));
+    }
+
+    return ptr;
+}
+
+void xen_be_unmap_grant_refs(struct XenDevice *xendev, void *ptr,
+                             unsigned int nr_refs)
+{
+    assert(xendev->ops->flags & DEVOPS_FLAG_NEED_GNTDEV);
+
+    if (xengnttab_unmap(xendev->gnttabdev, ptr, nr_refs)) {
+        xen_pv_printf(xendev, 0, "xengnttab_unmap failed: %s\n",
+                      strerror(errno));
+    }
+}
+
+int xen_be_copy_grant_refs(struct XenDevice *xendev,
+                           bool to_domain,
+                           XenGrantCopySegment segs[],
+                           unsigned int nr_segs)
+{
+    xengnttab_grant_copy_segment_t *xengnttab_segs;
+    unsigned int i;
+    int rc;
+
+    assert(xendev->ops->flags & DEVOPS_FLAG_NEED_GNTDEV);
+
+    xengnttab_segs = g_new0(xengnttab_grant_copy_segment_t, nr_segs);
+
+    for (i = 0; i < nr_segs; i++) {
+        XenGrantCopySegment *seg = &segs[i];
+        xengnttab_grant_copy_segment_t *xengnttab_seg = &xengnttab_segs[i];
+
+        if (to_domain) {
+            xengnttab_seg->flags = GNTCOPY_dest_gref;
+            xengnttab_seg->dest.foreign.domid = xen_domid;
+            xengnttab_seg->dest.foreign.ref = seg->dest.foreign.ref;
+            xengnttab_seg->dest.foreign.offset = seg->dest.foreign.offset;
+            xengnttab_seg->source.virt = seg->source.virt;
+        } else {
+            xengnttab_seg->flags = GNTCOPY_source_gref;
+            xengnttab_seg->source.foreign.domid = xen_domid;
+            xengnttab_seg->source.foreign.ref = seg->source.foreign.ref;
+            xengnttab_seg->source.foreign.offset =
+                seg->source.foreign.offset;
+            xengnttab_seg->dest.virt = seg->dest.virt;
+        }
+
+        xengnttab_seg->len = seg->len;
+    }
+
+    rc = xengnttab_grant_copy(xendev->gnttabdev, nr_segs, xengnttab_segs);
+
+    if (rc) {
+        xen_pv_printf(xendev, 0, "xengnttab_copy failed: %s\n",
+                      strerror(errno));
+    }
+
+    for (i = 0; i < nr_segs; i++) {
+        xengnttab_grant_copy_segment_t *xengnttab_seg =
+            &xengnttab_segs[i];
+
+        if (xengnttab_seg->status != GNTST_okay) {
+            xen_pv_printf(xendev, 0, "segment[%u] status: %d\n", i,
+                          xengnttab_seg->status);
+            rc = -1;
+        }
+    }
+
+    g_free(xengnttab_segs);
+    return rc;
+}
+
 /*
  * get xen backend device, allocate a new one if it doesn't exist.
  */
@@ -149,18 +246,6 @@ static struct XenDevice *xen_be_get_xendev(const char *type, int dom, int dev,
     }
     qemu_set_cloexec(xenevtchn_fd(xendev->evtchndev));
 
-    if (ops->flags & DEVOPS_FLAG_NEED_GNTDEV) {
-        xendev->gnttabdev = xengnttab_open(NULL, 0);
-        if (xendev->gnttabdev == NULL) {
-            xen_pv_printf(NULL, 0, "can't open gnttab device\n");
-            xenevtchn_close(xendev->evtchndev);
-            qdev_unplug(DEVICE(xendev), NULL);
-            return NULL;
-        }
-    } else {
-        xendev->gnttabdev = NULL;
-    }
-
     xen_pv_insert_xendev(xendev);
 
     if (xendev->ops->alloc) {
@@ -322,6 +407,16 @@ static int xen_be_try_initialise(struct XenDevice *xendev)
         }
     }
 
+    if (xendev->ops->flags & DEVOPS_FLAG_NEED_GNTDEV) {
+        xendev->gnttabdev = xengnttab_open(NULL, 0);
+        if (xendev->gnttabdev == NULL) {
+            xen_pv_printf(NULL, 0, "can't open gnttab device\n");
+            return -1;
+        }
+    } else {
+        xendev->gnttabdev = NULL;
+    }
+
     if (xendev->ops->initialise) {
         rc = xendev->ops->initialise(xendev);
     }
@@ -369,6 +464,10 @@ static void xen_be_disconnect(struct XenDevice *xendev, enum xenbus_state state)
         xendev->ops->disconnect) {
         xendev->ops->disconnect(xendev);
     }
+    if (xendev->gnttabdev) {
+        xengnttab_close(xendev->gnttabdev);
+        xendev->gnttabdev = NULL;
+    }
     if (xendev->be_state != state) {
         xen_be_set_state(xendev, state);
     }
diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
index 3a27692407..29bf1c3bc3 100644
--- a/include/hw/xen/xen_backend.h
+++ b/include/hw/xen/xen_backend.h
@@ -42,6 +42,39 @@ void xen_be_register_common(void);
 int xen_be_register(const char *type, struct XenDevOps *ops);
 int xen_be_set_state(struct XenDevice *xendev, enum xenbus_state state);
 int xen_be_bind_evtchn(struct XenDevice *xendev);
+void xen_be_set_max_grant_refs(struct XenDevice *xendev,
+                               unsigned int nr_refs);
+void *xen_be_map_grant_refs(struct XenDevice *xendev, uint32_t *refs,
+                            unsigned int nr_refs, int prot);
+void xen_be_unmap_grant_refs(struct XenDevice *xendev, void *ptr,
+                             unsigned int nr_refs);
+
+typedef struct XenGrantCopySegment {
+    union {
+        void *virt;
+        struct {
+            uint32_t ref;
+            off_t offset;
+        } foreign;
+    } source, dest;
+    size_t len;
+} XenGrantCopySegment;
+
+int xen_be_copy_grant_refs(struct XenDevice *xendev,
+                           bool to_domain, XenGrantCopySegment segs[],
+                           unsigned int nr_segs);
+
+static inline void *xen_be_map_grant_ref(struct XenDevice *xendev,
+                                         uint32_t ref, int prot)
+{
+    return xen_be_map_grant_refs(xendev, &ref, 1, prot);
+}
+
+static inline void xen_be_unmap_grant_ref(struct XenDevice *xendev,
+                                          void *ptr)
+{
+    return xen_be_unmap_grant_refs(xendev, ptr, 1);
+}
 
 /* actual backend drivers */
 extern struct XenDevOps xen_console_ops;      /* xen_console.c     */