expose migration region (#305)

This patch exposes the fact that live migration is implemented as a
special device region. Hiding this from the user doesn't offer much
benefit since it only takes just a little bit of extra code for the user
to handle it as a region. We do keep the migration callback
functionality since this feature substantially simplifies supporting
live migration from the device implementation's perspective.

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
Co-authored-by: John Levon <john.levon@nutanix.com>

1 files changed, 12 insertions, 15 deletions

diff --git a/samples/client.c b/samples/client.c
index 92d86e0..d9b6661 100644
--- a/samples/client.c
+++ b/samples/client.c
@@ -209,7 +209,7 @@ send_device_reset(int sock)
 /* returns whether a VFIO migration capability is found */
 static bool
 get_region_vfio_caps(struct vfio_info_cap_header *header,
-                     struct vfio_region_info_cap_sparse_mmap *sparse)
+                     struct vfio_region_info_cap_sparse_mmap **sparse)
 {
     struct vfio_region_info_cap_type *type;
     unsigned int i;
@@ -218,12 +218,13 @@ get_region_vfio_caps(struct vfio_info_cap_header *header,
     while (true) {
         switch (header->id) {
             case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
-                sparse = (struct vfio_region_info_cap_sparse_mmap*)header;
+                *sparse = (struct vfio_region_info_cap_sparse_mmap *)header;
                 printf("%s: Sparse cap nr_mmap_areas %d\n", __func__,
-                       sparse->nr_areas);
-                for (i = 0; i < sparse->nr_areas; i++) {
+                       (*sparse)->nr_areas);
+                for (i = 0; i < (*sparse)->nr_areas; i++) {
                     printf("%s: area %d offset %#llx size %llu\n", __func__,
-                           i, sparse->areas[i].offset, sparse->areas[i].size);
+                           i, (*sparse)->areas[i].offset,
+                           (*sparse)->areas[i].size);
                 }
                 break;
             case VFIO_REGION_INFO_CAP_TYPE:
@@ -261,14 +262,10 @@ do_get_device_region_info(int sock, struct vfio_region_info *region_info,
 }
 
 static void
-mmap_sparse_areas(int *fds, size_t nr_fds,
-                  struct vfio_region_info_cap_sparse_mmap *sparse)
+mmap_sparse_areas(int *fds, struct vfio_region_info_cap_sparse_mmap *sparse)
 {
     size_t i;
 
-    assert(nr_fds == 2);
-    assert(sparse->nr_areas == 2);
-
     for (i = 0; i < sparse->nr_areas; i++) {
 
         ssize_t ret;
@@ -318,9 +315,6 @@ get_device_region_info(int sock, uint32_t index)
         region_info->index = index;
         do_get_device_region_info(sock, region_info, fds, &nr_fds);
         assert(region_info->argsz == size);
-        assert(nr_fds == 2);
-        assert(fds[0] >= 0);
-        assert(fds[1] >= 0);
     } else {
         nr_fds = 0;
     }
@@ -332,9 +326,12 @@ get_device_region_info(int sock, uint32_t index)
     if (cap_sz) {
         struct vfio_region_info_cap_sparse_mmap *sparse = NULL;
         if (get_region_vfio_caps((struct vfio_info_cap_header*)(region_info + 1),
-                                 sparse)) {
+                                 &sparse)) {
             if (sparse != NULL) {
-                mmap_sparse_areas(fds, nr_fds, sparse);
+                assert((index == VFU_PCI_DEV_BAR1_REGION_IDX && nr_fds == 2) ||
+                       (index == VFU_PCI_DEV_MIGR_REGION_IDX && nr_fds == 1));
+                assert(nr_fds == sparse->nr_areas);
+                mmap_sparse_areas(fds, sparse);
             }
             return true;
         }