qemu-io: Allow larger write zeroes under no fallback

[qmiga/qemu.git] / qemu-img.c

diff --git a/qemu-img.c b/qemu-img.c
index f036a1d..6fe2466 100644 (file)
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -902,7 +902,7 @@ static void common_block_job_cb(void *opaque, int ret)
 static void run_block_job(BlockJob *job, Error **errp)
 {
     uint64_t progress_current, progress_total;
-    AioContext *aio_context = blk_get_aio_context(job->blk);
+    AioContext *aio_context = block_job_get_aio_context(job);
     int ret = 0;
 
     aio_context_acquire(aio_context);
@@ -1171,19 +1171,34 @@ static int is_allocated_sectors(const uint8_t *buf, int n, int *pnum,
         }
     }
 
+    if (i == n) {
+        /*
+         * The whole buf is the same.
+         * No reason to split it into chunks, so return now.
+         */
+        *pnum = i;
+        return !is_zero;
+    }
+
     tail = (sector_num + i) & (alignment - 1);
     if (tail) {
         if (is_zero && i <= tail) {
-            /* treat unallocated areas which only consist
-             * of a small tail as allocated. */
+            /*
+             * For sure next sector after i is data, and it will rewrite this
+             * tail anyway due to RMW. So, let's just write data now.
+             */
             is_zero = false;
         }
         if (!is_zero) {
-            /* align up end offset of allocated areas. */
+            /* If possible, align up end offset of allocated areas. */
             i += alignment - tail;
             i = MIN(i, n);
         } else {
-            /* align down end offset of zero areas. */
+            /*
+             * For sure next sector after i is data, and it will rewrite this
+             * tail anyway due to RMW. Better is avoid RMW and write zeroes up
+             * to aligned bound.
+             */
             i -= tail;
         }
     }