add mappable bit in DMA segment (#215)

remove duplicate code for initializing DMA segment,  mark DMA segment whether it's mappable, plus basic unit test for dma_addr_to_sg

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>

2 files changed, 17 insertions, 14 deletions

diff --git a/lib/dma.c b/lib/dma.c
index 0bb623c..69b3fe5 100644
--- a/lib/dma.c
+++ b/lib/dma.c
@@ -375,13 +375,7 @@ _dma_addr_sg_split(const dma_controller_t *dma,
                 size_t region_len = MIN(region_end - dma_addr, len);
 
                 if (cnt < max_sg) {
-                    sg[cnt].dma_addr = region->dma_addr;
-                    sg[cnt].region = idx;
-                    sg[cnt].offset = dma_addr - region->dma_addr;
-                    sg[cnt].length = region_len;
-                    if (_dma_should_mark_dirty(dma, prot)) {
-                        _dma_mark_dirty(dma, region, sg);
-                    }
+                    dma_init_sg(dma, sg, dma_addr, region_len, prot, idx);
                 }
 
                 cnt++;
diff --git a/lib/dma.h b/lib/dma.h
index aeed9bb..7bab3da 100644
--- a/lib/dma.h
+++ b/lib/dma.h
@@ -181,6 +181,21 @@ _dma_mark_dirty(const dma_controller_t *dma, const dma_memory_region_t *region,
     }
 }
 
+static inline void
+dma_init_sg(const dma_controller_t *dma, dma_sg_t *sg, dma_addr_t dma_addr,
+            uint32_t len, int prot, int region_index)
+{
+    const dma_memory_region_t *const region = &dma->regions[region_index];
+    sg->dma_addr = region->dma_addr;
+    sg->region = region_index;
+    sg->offset = dma_addr - region->dma_addr;
+    sg->length = len;
+    if (_dma_should_mark_dirty(dma, prot)) {
+        _dma_mark_dirty(dma, region, sg);
+    }
+    sg->mappable = region->virt_addr != NULL;
+}
+
 /* Takes a linear dma address span and returns a sg list suitable for DMA.
  * A single linear dma address span may need to be split into multiple
  * scatter gather regions due to limitations of how memory can be mapped.
@@ -207,13 +222,7 @@ dma_addr_to_sg(const dma_controller_t *dma,
     if (likely(max_sg > 0 && len > 0 &&
                dma_addr >= region->dma_addr && dma_addr + len <= region_end &&
                region_hint < dma->nregions)) {
-        sg->dma_addr = region->dma_addr;
-        sg->region = region_hint;
-        sg->offset = dma_addr - region->dma_addr;
-        sg->length = len;
-        if (_dma_should_mark_dirty(dma, prot)) {
-            _dma_mark_dirty(dma, region, sg);
-        }
+        dma_init_sg(dma, sg, dma_addr, len, prot, region_hint);
         return 1;
     }
     // Slow path: search through regions.