[PATCH v3 02/10] Add vhost-user helper to get MemoryRegion data

[Raphael Norwitz <raphael.norwitz@nutanix.com>]

When setting the memory tables, qemu uses a memory region's userspace
address to look up the region's MemoryRegion struct. Among other things,
the MemoryRegion contains the region's offset and associated file
descriptor, all of which need to be sent to the backend.

With VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS, this logic will be
needed in multiple places, so before feature support is added it
should be moved to a helper function.

This helper is also used to simplify the vhost_user_can_merge()
function.

Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
---
 hw/virtio/vhost-user.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index ee6d1ed..dacf5bb 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -407,6 +407,18 @@ static int vhost_user_set_log_base(struct vhost_dev *dev, uint64_t base,
     return 0;
 }
 
+static MemoryRegion *vhost_user_get_mr_data(uint64_t addr, ram_addr_t *offset,
+                                            int *fd)
+{
+    MemoryRegion *mr;
+
+    assert((uintptr_t)addr == addr);
+    mr = memory_region_from_host((void *)(uintptr_t)addr, offset);
+    *fd = memory_region_get_fd(mr);
+
+    return mr;
+}
+
 static void vhost_user_fill_msg_region(VhostUserMemoryRegion *dst,
                                        struct vhost_memory_region *src)
 {
@@ -432,10 +444,7 @@ static int vhost_user_fill_set_mem_table_msg(struct vhost_user *u,
     for (i = 0; i < dev->mem->nregions; ++i) {
         reg = dev->mem->regions + i;
 
-        assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
-        mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
-                                     &offset);
-        fd = memory_region_get_fd(mr);
+        mr = vhost_user_get_mr_data(reg->userspace_addr, &offset, &fd);
         if (fd > 0) {
             if (track_ramblocks) {
                 assert(*fd_num < VHOST_MEMORY_MAX_NREGIONS);
@@ -1550,13 +1559,9 @@ static bool vhost_user_can_merge(struct vhost_dev *dev,
 {
     ram_addr_t offset;
     int mfd, rfd;
-    MemoryRegion *mr;
-
-    mr = memory_region_from_host((void *)(uintptr_t)start1, &offset);
-    mfd = memory_region_get_fd(mr);
 
-    mr = memory_region_from_host((void *)(uintptr_t)start2, &offset);
-    rfd = memory_region_get_fd(mr);
+    (void)vhost_user_get_mr_data(start1, &offset, &mfd);
+    (void)vhost_user_get_mr_data(start2, &offset, &rfd);
 
     return mfd == rfd;
 }
-- 
1.8.3.1