dma: cleanup dma_{map,unmap}_sg (#591)

* dma: cleanup dma_{map,unmap}_sg

Instead of using index to traverse sg and iovec, better to use it as
pointers. It's more readable and less prone from coding mistakes.
Also adding unit tests for the same.

Signed-off-by: Swapnil Ingle <swapnil.ingle@nutanix.com>
Reviewed-by: John Levon <john.levon@nutanix.com>

1 files changed, 28 insertions, 20 deletions

diff --git a/lib/dma.h b/lib/dma.h
index 895e14f..190a016 100644
--- a/lib/dma.h
+++ b/lib/dma.h
@@ -229,35 +229,38 @@ dma_map_sg(dma_controller_t *dma, dma_sg_t *sg, struct iovec *iov,
            int cnt)
 {
     dma_memory_region_t *region;
-    int i;
 
     assert(dma != NULL);
     assert(sg != NULL);
     assert(iov != NULL);
+    assert(cnt > 0);
 
-    for (i = 0; i < cnt; i++) {
-        if (sg[i].region >= dma->nregions) {
+    do {
+        if (sg->region >= dma->nregions) {
             return ERROR_INT(EINVAL);
         }
-        region = &dma->regions[sg[i].region];
+        region = &dma->regions[sg->region];
 
         if (region->info.vaddr == NULL) {
             return ERROR_INT(EFAULT);
         }
 
-        if (sg[i].writeable) {
+        if (sg->writeable) {
             if (dma->dirty_pgsize > 0) {
-                _dma_mark_dirty(dma, region, &sg[i]);
+                _dma_mark_dirty(dma, region, sg);
             }
-            LIST_INSERT_HEAD(&dma->maps, &sg[i], entry);
+            LIST_INSERT_HEAD(&dma->maps, sg, entry);
         }
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "map %p-%p",
-                sg[i].dma_addr + sg[i].offset,
-                sg[i].dma_addr + sg[i].offset + sg[i].length);
-        iov[i].iov_base = region->info.vaddr + sg[i].offset;
-        iov[i].iov_len = sg[i].length;
+                sg->dma_addr + sg->offset,
+                sg->dma_addr + sg->offset + sg->length);
+        iov->iov_base = region->info.vaddr + sg->offset;
+        iov->iov_len = sg->length;
         region->refcnt++;
-    }
+
+        sg++;
+        iov++;
+    } while (--cnt > 0);
 
     return 0;
 }
@@ -266,9 +269,13 @@ static inline void
 dma_unmap_sg(dma_controller_t *dma, const dma_sg_t *sg,
 	     UNUSED struct iovec *iov, int cnt)
 {
-    int i;
 
-    for (i = 0; i < cnt; i++) {
+    assert(dma != NULL);
+    assert(sg != NULL);
+    assert(iov != NULL);
+    assert(cnt > 0);
+
+    do {
         dma_memory_region_t *r;
         /*
          * FIXME this double loop will be removed if we replace the array with
@@ -276,20 +283,21 @@ dma_unmap_sg(dma_controller_t *dma, const dma_sg_t *sg,
          */
         for (r = dma->regions;
              r < dma->regions + dma->nregions &&
-             r->info.iova.iov_base != sg[i].dma_addr;
+             r->info.iova.iov_base != sg->dma_addr;
              r++);
         if (r > dma->regions + dma->nregions) {
             /* bad region */
             continue;
         }
-        if (sg[i].writeable) {
-            LIST_REMOVE(&sg[i], entry);
+        if (sg->writeable) {
+            LIST_REMOVE(sg, entry);
         }
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "unmap %p-%p",
-                sg[i].dma_addr + sg[i].offset,
-                sg[i].dma_addr + sg[i].offset + sg[i].length);
+                sg->dma_addr + sg->offset,
+                sg->dma_addr + sg->offset + sg->length);
         r->refcnt--;
-    }
+        sg++;
+    } while (--cnt > 0);
 }
 
 int