[PATCH v2 3/5] libvhost-user: Simplify VHOST_USER_REM_MEM_REG

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

From: David Hildenbrand <david@redhat.com>

Let's avoid having to manually copy all elements. Copy only the ones
necessary to close the hole and perform the operation in-place without
a second array.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 subprojects/libvhost-user/libvhost-user.c | 30 +++++++++++------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvhost-user/libvhost-user.c
index d61285e991..77ddc96ddf 100644
--- a/subprojects/libvhost-user/libvhost-user.c
+++ b/subprojects/libvhost-user/libvhost-user.c
@@ -802,10 +802,8 @@ static inline bool reg_equal(VuDevRegion *vudev_reg,
 
 static bool
 vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
-    int i, j;
-    bool found = false;
-    VuDevRegion shadow_regions[VHOST_USER_MAX_RAM_SLOTS] = {};
     VhostUserMemoryRegion m = vmsg->payload.memreg.region, *msg_region = &m;
+    int i;
 
     if (vmsg->fd_num != 1 ||
         vmsg->size != sizeof(vmsg->payload.memreg)) {
@@ -823,28 +821,28 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
     DPRINT("    mmap_offset      0x%016"PRIx64"\n",
            msg_region->mmap_offset);
 
-    for (i = 0, j = 0; i < dev->nregions; i++) {
-        if (!reg_equal(&dev->regions[i], msg_region)) {
-            shadow_regions[j].gpa = dev->regions[i].gpa;
-            shadow_regions[j].size = dev->regions[i].size;
-            shadow_regions[j].qva = dev->regions[i].qva;
-            shadow_regions[j].mmap_addr = dev->regions[i].mmap_addr;
-            shadow_regions[j].mmap_offset = dev->regions[i].mmap_offset;
-            j++;
-        } else {
-            found = true;
+    for (i = 0; i < dev->nregions; i++) {
+        if (reg_equal(&dev->regions[i], msg_region)) {
             VuDevRegion *r = &dev->regions[i];
             void *m = (void *) (uintptr_t) r->mmap_addr;
 
             if (m) {
                 munmap(m, r->size + r->mmap_offset);
             }
+
+            break;
         }
     }
 
-    if (found) {
-        memcpy(dev->regions, shadow_regions,
-               sizeof(VuDevRegion) * VHOST_USER_MAX_RAM_SLOTS);
+    if (i < dev->nregions) {
+        /*
+         * Shift all affected entries by 1 to close the hole at index i and
+         * zero out the last entry.
+         */
+        memmove(dev->regions + i, dev->regions + i + 1,
+               sizeof(VuDevRegion) * (dev->nregions - i - 1));
+        memset(dev->regions + dev->nregions - 1, 0,
+               sizeof(VuDevRegion));
         DPRINT("Successfully removed a region\n");
         dev->nregions--;
         vmsg_set_reply_u64(vmsg, 0);
-- 
2.20.1