Re: [Qemu-devel] [PATCH v4 18/21] backup: Switch backup_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 backups to track by bytes instead of sectors
> (although we are still guaranteed that we iterate by steps that
> are cluster-aligned).
> 
> Signed-off-by: Eric Blake 
> Reviewed-by: John Snow 
> Reviewed-by: Jeff Cody 

Reviewed-by: Kevin Wolf 

[Qemu-devel] [PATCH v4 18/21] backup: Switch backup_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 backups to track by bytes instead of sectors
(although we are still guaranteed that we iterate by steps that
are cluster-aligned).

Signed-off-by: Eric Blake 
Reviewed-by: John Snow 
Reviewed-by: Jeff Cody 
---
v2-v4: no change
---
 block/backup.c | 32 +++-
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index c029d44..04def91 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -370,11 +370,10 @@ static int coroutine_fn 
backup_run_incremental(BackupBlockJob *job)
 int ret = 0;
 int clusters_per_iter;
 uint32_t granularity;
-int64_t sector;
+int64_t offset;
 int64_t cluster;
 int64_t end;
 int64_t last_cluster = -1;
-int64_t sectors_per_cluster = cluster_size_sectors(job);
 BdrvDirtyBitmapIter *dbi;

 granularity = bdrv_dirty_bitmap_granularity(job->sync_bitmap);
@@ -382,8 +381,8 @@ static int coroutine_fn 
backup_run_incremental(BackupBlockJob *job)
 dbi = bdrv_dirty_iter_new(job->sync_bitmap, 0);

 /* Find the next dirty sector(s) */
-while ((sector = bdrv_dirty_iter_next(dbi)) != -1) {
-cluster = sector / sectors_per_cluster;
+while ((offset = bdrv_dirty_iter_next(dbi) * BDRV_SECTOR_SIZE) >= 0) {
+cluster = offset / job->cluster_size;

 /* Fake progress updates for any clusters we skipped */
 if (cluster != last_cluster + 1) {
@@ -410,7 +409,8 @@ static int coroutine_fn 
backup_run_incremental(BackupBlockJob *job)
 /* If the bitmap granularity is smaller than the backup granularity,
  * we need to advance the iterator pointer to the next cluster. */
 if (granularity < job->cluster_size) {
-bdrv_set_dirty_iter(dbi, cluster * sectors_per_cluster);
+bdrv_set_dirty_iter(dbi,
+cluster * job->cluster_size / 
BDRV_SECTOR_SIZE);
 }

 last_cluster = cluster - 1;
@@ -432,17 +432,15 @@ static void coroutine_fn backup_run(void *opaque)
 BackupBlockJob *job = opaque;
 BackupCompleteData *data;
 BlockDriverState *bs = blk_bs(job->common.blk);
-int64_t start, end;
+int64_t offset;
 int64_t sectors_per_cluster = cluster_size_sectors(job);
 int ret = 0;

 QLIST_INIT(>inflight_reqs);
 qemu_co_rwlock_init(>flush_rwlock);

-start = 0;
-end = DIV_ROUND_UP(job->common.len, job->cluster_size);
-
-job->done_bitmap = bitmap_new(end);
+job->done_bitmap = bitmap_new(DIV_ROUND_UP(job->common.len,
+   job->cluster_size));

 job->before_write.notify = backup_before_write_notify;
 bdrv_add_before_write_notifier(bs, >before_write);
@@ -457,7 +455,8 @@ static void coroutine_fn backup_run(void *opaque)
 ret = backup_run_incremental(job);
 } else {
 /* Both FULL and TOP SYNC_MODE's require copying.. */
-for (; start < end; start++) {
+for (offset = 0; offset < job->common.len;
+ offset += job->cluster_size) {
 bool error_is_read;
 int alloced = 0;

@@ -480,8 +479,8 @@ static void coroutine_fn backup_run(void *opaque)
  * needed but at some point that is always the case. */
 alloced =
 bdrv_is_allocated(bs,
-start * sectors_per_cluster + i,
-sectors_per_cluster - i, );
+  (offset >> BDRV_SECTOR_BITS) + i,
+  sectors_per_cluster - i, );
 i += n;

 if (alloced || n == 0) {
@@ -499,9 +498,8 @@ static void coroutine_fn backup_run(void *opaque)
 if (alloced < 0) {
 ret = alloced;
 } else {
-ret = backup_do_cow(job, start * job->cluster_size,
-job->cluster_size, _is_read,
-false);
+ret = backup_do_cow(job, offset, job->cluster_size,
+_is_read, false);
 }
 if (ret < 0) {
 /* Depending on error action, fail now or retry cluster */
@@ -510,7 +508,7 @@ static void coroutine_fn backup_run(void *opaque)
 if (action == BLOCK_ERROR_ACTION_REPORT) {
 break;
 } else {
-start--;
+offset -= job->cluster_size;
 continue;
 }
 }
-- 
2.9.4