[Qemu-devel] [PATCH 04/17] stream: Switch stream_run() to byte-based

[Eric Blake]

We are gradually converting to byte-based interfaces, as they are
easier to reason about than sector-based.  Change the internal
loop iteration of streaming to track by bytes instead of sectors
(although we are still guaranteed that we iterate by steps that
are sector-aligned).

Signed-off-by: Eric Blake <address@hidden>
---
 block/stream.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/block/stream.c b/block/stream.c
index 5acef6d..3ed4fef 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque)
     BlockBackend *blk = s->common.blk;
     BlockDriverState *bs = blk_bs(blk);
     BlockDriverState *base = s->base;
-    int64_t sector_num = 0;
-    int64_t end = -1;
+    int64_t offset = 0;
     uint64_t delay_ns = 0;
     int error = 0;
     int ret = 0;
-    int n = 0;
+    int n = 0; /* sectors */
     void *buf;

     if (!bs->backing) {
@@ -126,7 +125,6 @@ static void coroutine_fn stream_run(void *opaque)
         goto out;
     }

-    end = s->common.len >> BDRV_SECTOR_BITS;
     buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);

     /* Turn on copy-on-read for the whole block device so that guest read
@@ -138,7 +136,7 @@ static void coroutine_fn stream_run(void *opaque)
         bdrv_enable_copy_on_read(bs);
     }

-    for (sector_num = 0; sector_num < end; sector_num += n) {
+    for ( ; offset < s->common.len; offset += n * BDRV_SECTOR_SIZE) {
         bool copy;

         /* Note that even when no rate limit is applied we need to yield
@@ -151,28 +149,26 @@ static void coroutine_fn stream_run(void *opaque)

         copy = false;

-        ret = bdrv_is_allocated(bs, sector_num,
+        ret = bdrv_is_allocated(bs, offset / BDRV_SECTOR_SIZE,
                                 STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);
         if (ret == 1) {
             /* Allocated in the top, no need to copy.  */
         } else if (ret >= 0) {
             /* Copy if allocated in the intermediate images.  Limit to the
-             * known-unallocated area [sector_num, sector_num+n).  */
+             * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
             ret = bdrv_is_allocated_above(backing_bs(bs), base,
-                                          sector_num, n, &n);
+                                          offset / BDRV_SECTOR_SIZE, n, &n);

             /* Finish early if end of backing file has been reached */
             if (ret == 0 && n == 0) {
-                n = end - sector_num;
+                n = (s->common.len - offset) / BDRV_SECTOR_SIZE;
             }

             copy = (ret == 1);
         }
-        trace_stream_one_iteration(s, sector_num * BDRV_SECTOR_SIZE,
-                                   n * BDRV_SECTOR_SIZE, ret);
+        trace_stream_one_iteration(s, offset, n * BDRV_SECTOR_SIZE, ret);
         if (copy) {
-            ret = stream_populate(blk, sector_num * BDRV_SECTOR_SIZE,
-                                  n * BDRV_SECTOR_SIZE, buf);
+            ret = stream_populate(blk, offset, n * BDRV_SECTOR_SIZE, buf);
         }
         if (ret < 0) {
             BlockErrorAction action =
@@ -211,7 +207,7 @@ out:
     /* Modify backing chain and close BDSes in main loop */
     data = g_malloc(sizeof(*data));
     data->ret = ret;
-    data->reached_end = sector_num == end;
+    data->reached_end = offset == s->common.len;
     block_job_defer_to_main_loop(&s->common, stream_complete, data);
 }

-- 
2.9.3