Re: [Qemu-devel] [PATCH v4 05/21] stream: Switch stream_run() to byte-based

[Kevin Wolf]

Am 05.07.2017 um 23:08 hat Eric Blake geschrieben:
> 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 
> Reviewed-by: John Snow 
> Reviewed-by: Jeff Cody 

Reviewed-by: Kevin Wolf 

[Qemu-devel] [PATCH v4 05/21] 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 
Reviewed-by: John Snow 
Reviewed-by: Jeff Cody 

---
v4: avoid reached_end change by rebasing to earlier changes [Kevin], R-b kept
v2-v3: no change
---
 block/stream.c | 22 +-
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/block/stream.c b/block/stream.c
index 12f1659..e3dd2ac 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -107,12 +107,11 @@ 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) {
@@ -125,7 +124,6 @@ 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
@@ -137,7 +135,7 @@ 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
@@ -150,28 +148,26 @@ 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, );
 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, );
+  offset / BDRV_SECTOR_SIZE, 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 =
-- 
2.9.4