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Re: [Qemu-devel] [PATCH v11 09/13] qmp: Add support of "dirty-bitmap" sy

From: John Snow
Subject: Re: [Qemu-devel] [PATCH v11 09/13] qmp: Add support of "dirty-bitmap" sync mode for drive-backup
Date: Tue, 13 Jan 2015 12:50:53 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 


On 01/13/2015 04:37 AM, Fam Zheng wrote:

On Mon, 01/12 11:31, John Snow wrote:

For "dirty-bitmap" sync mode, the block job will iterate through the
given dirty bitmap to decide if a sector needs backup (backup all the
dirty clusters and skip clean ones), just as allocation conditions of
"top" sync mode.

Signed-off-by: Fam Zheng <address@hidden>
Signed-off-by: John Snow <address@hidden>
---
  block.c                   |   5 ++
  block/backup.c            | 120 ++++++++++++++++++++++++++++++++++++++--------
  block/mirror.c            |   4 ++
  blockdev.c                |  14 +++++-
  hmp.c                     |   3 +-
  include/block/block.h     |   1 +
  include/block/block_int.h |   2 +
  qapi/block-core.json      |  11 +++--
  qmp-commands.hx           |   7 +--
  9 files changed, 137 insertions(+), 30 deletions(-)

diff --git a/block.c b/block.c
index 3f33b9d..5eb6788 100644
--- a/block.c
+++ b/block.c
@@ -5633,6 +5633,11 @@ static void bdrv_reset_dirty(BlockDriverState *bs, 
int64_t cur_sector,
      }
  }

+void bdrv_set_dirty_iter(HBitmapIter *hbi, int64_t offset)
+{
+    hbitmap_iter_init(hbi, hbi->hb, offset);


What's the reason for this indirection? Can caller just use hbitmap_iter_init?
Essentially it is just a rename of hbitmap_iter_init to make its usage here clear, that we are manually advancing the pointer. How we accomplish that (hbitmap_iter_init) is an implementation detail.
Yes, I can just call this directly from block/backup, but at the time I was less sure of how I would advance the pointer, so I created a wrapper where I could change details as needed, if I needed to. 


+}
+
  int64_t bdrv_get_dirty_count(BlockDriverState *bs, BdrvDirtyBitmap *bitmap)
  {
      return hbitmap_count(bitmap->bitmap);
diff --git a/block/backup.c b/block/backup.c
index 792e655..0626a3e 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -37,6 +37,8 @@ typedef struct CowRequest {
  typedef struct BackupBlockJob {
      BlockJob common;
      BlockDriverState *target;
+    /* bitmap for sync=dirty-bitmap */
+    BdrvDirtyBitmap *sync_bitmap;
      MirrorSyncMode sync_mode;
      RateLimit limit;
      BlockdevOnError on_source_error;
@@ -242,6 +244,31 @@ static void backup_complete(BlockJob *job, void *opaque)
      g_free(data);
  }

+static bool coroutine_fn yield_and_check(BackupBlockJob *job)
+{
+    if (block_job_is_cancelled(&job->common)) {
+        return true;
+    }
+
+    /* we need to yield so that qemu_aio_flush() returns.
+     * (without, VM does not reboot)
+     */
+    if (job->common.speed) {
+        uint64_t delay_ns = ratelimit_calculate_delay(&job->limit,
+                                                      job->sectors_read);
+        job->sectors_read = 0;
+        block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, delay_ns);
+    } else {
+        block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
+    }
+
+    if (block_job_is_cancelled(&job->common)) {
+        return true;
+    }
+
+    return false;
+}
+
  static void coroutine_fn backup_run(void *opaque)
  {
      BackupBlockJob *job = opaque;
@@ -254,13 +281,13 @@ static void coroutine_fn backup_run(void *opaque)
      };
      int64_t start, end;
      int ret = 0;
+    bool error_is_read;

      QLIST_INIT(&job->inflight_reqs);
      qemu_co_rwlock_init(&job->flush_rwlock);

      start = 0;
-    end = DIV_ROUND_UP(job->common.len / BDRV_SECTOR_SIZE,
-                       BACKUP_SECTORS_PER_CLUSTER);
+    end = DIV_ROUND_UP(job->common.len, BACKUP_CLUSTER_SIZE);

      job->bitmap = hbitmap_alloc(end, 0);

@@ -278,28 +305,45 @@ static void coroutine_fn backup_run(void *opaque)
              qemu_coroutine_yield();
              job->common.busy = true;
          }
+    } else if (job->sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
+        /* Dirty Bitmap sync has a slightly different iteration method */
+        HBitmapIter hbi;
+        int64_t sector;
+        int64_t cluster;
+        bool polyrhythmic;
+
+        bdrv_dirty_iter_init(bs, job->sync_bitmap, &hbi);
+        /* Does the granularity happen to match our backup cluster size? */
+        polyrhythmic = (bdrv_dirty_bitmap_granularity(bs, job->sync_bitmap) !=
+                        BACKUP_CLUSTER_SIZE);
+
+        /* Find the next dirty /sector/ and copy that /cluster/ */
+        while ((sector = hbitmap_iter_next(&hbi)) != -1) {
+            if (yield_and_check(job)) {
+                goto leave;
+            }
+            cluster = sector / BACKUP_SECTORS_PER_CLUSTER;
+
+            do {
+                ret = backup_do_cow(bs, cluster * BACKUP_SECTORS_PER_CLUSTER,
+                                    BACKUP_SECTORS_PER_CLUSTER, 
&error_is_read);
+                if ((ret < 0) &&
+                    backup_error_action(job, error_is_read, -ret) ==
+                    BLOCK_ERROR_ACTION_REPORT) {
+                    goto leave;
+                }
+            } while (ret < 0);
+
+            /* Advance (or rewind) our iterator if we need to. */
+            if (polyrhythmic) {
+                bdrv_set_dirty_iter(&hbi,
+                                    (cluster + 1) * 
BACKUP_SECTORS_PER_CLUSTER);
+            }
+        }
      } else {
          /* Both FULL and TOP SYNC_MODE's require copying.. */
          for (; start < end; start++) {
-            bool error_is_read;
-
-            if (block_job_is_cancelled(&job->common)) {
-                break;
-            }
-
-            /* we need to yield so that qemu_aio_flush() returns.
-             * (without, VM does not reboot)
-             */
-            if (job->common.speed) {
-                uint64_t delay_ns = ratelimit_calculate_delay(
-                        &job->limit, job->sectors_read);
-                job->sectors_read = 0;
-                block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 
delay_ns);
-            } else {
-                block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
-            }
-
-            if (block_job_is_cancelled(&job->common)) {
+            if (yield_and_check(job)) {
                  break;
              }

@@ -351,12 +395,23 @@ static void coroutine_fn backup_run(void *opaque)
          }
      }

+leave:
      notifier_with_return_remove(&before_write);

      /* wait until pending backup_do_cow() calls have completed */
      qemu_co_rwlock_wrlock(&job->flush_rwlock);
      qemu_co_rwlock_unlock(&job->flush_rwlock);

+    if (job->sync_bitmap) {
+        if (ret < 0) {
+            /* Merge the successor back into the parent, delete nothing. */
+            assert(bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL));


Why can't reclaim fail here? If we canassert, please move the expression out
because it has a side effect.
It shouldn't fail; if it does, something went very wrong. The only chance this has to fail is if the sync bitmap has no successor, but we explicitly installed one (and explicitly check that it succeeded) before going into the block backup.
I am not sure what other meaningful recovery could happen in this case, though we *could* just report an error and continue on, acknowledging that the BdrvDirtyBitmap is now compromised and of questionable validity. 

Does anyone have an error handling preference here?


+            bdrv_enable_dirty_bitmap(job->sync_bitmap);
+        } else {
+            /* Everything is fine, delete this bitmap and install the backup. 
*/
+            assert(bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL));
+        }
+    }
      hbitmap_free(job->bitmap);

      bdrv_iostatus_disable(target);
@@ -368,6 +423,7 @@ static void coroutine_fn backup_run(void *opaque)

  void backup_start(BlockDriverState *bs, BlockDriverState *target,
                    int64_t speed, MirrorSyncMode sync_mode,
+                  BdrvDirtyBitmap *sync_bitmap,
                    BlockdevOnError on_source_error,
                    BlockdevOnError on_target_error,
                    BlockCompletionFunc *cb, void *opaque,
@@ -386,6 +442,26 @@ void backup_start(BlockDriverState *bs, BlockDriverState 
*target,
          return;
      }

+    if (sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
+        if (!sync_bitmap) {
+            error_setg(errp, "must provide a valid bitmap name for "
+                             "\"dirty-bitmap\" sync mode");
+            return;
+        }
+
+        /* Create a new bitmap, and freeze/disable this one. */
+        if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
+            return;
+        }


There are two error paths in this function after this creation, need to release
it there?



Oh, yes. I will do two things:
(1) Add an optimization to reclaim such that if one of the bitmaps is empty, it just returns the other one, and 
(2) Add a reclaim call in the error pathway.


+
+    } else if (sync_bitmap) {
+        error_setg(errp,
+                   "a sync_bitmap was provided to backup_run, "
+                   "but received an incompatible sync_mode (%s)",
+                   MirrorSyncMode_lookup[sync_mode]);
+        return;
+    }
+
      len = bdrv_getlength(bs);
      if (len < 0) {
          error_setg_errno(errp, -len, "unable to get length for '%s'",
@@ -403,6 +479,8 @@ void backup_start(BlockDriverState *bs, BlockDriverState 
*target,
      job->on_target_error = on_target_error;
      job->target = target;
      job->sync_mode = sync_mode;
+    job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP ?
+                       sync_bitmap : NULL;
      job->common.len = len;
      job->common.co = qemu_coroutine_create(backup_run);
      qemu_coroutine_enter(job->common.co, job);
diff --git a/block/mirror.c b/block/mirror.c
index fc545f1..427c688 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -717,6 +717,10 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
      bool is_none_mode;
      BlockDriverState *base;

+    if (mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
+        error_setg(errp, "Sync mode 'dirty-bitmap' not supported");
+        return;
+    }
      is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
      base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
      mirror_start_job(bs, target, replaces,
diff --git a/blockdev.c b/blockdev.c
index 8dde72a..114a94c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1569,6 +1569,7 @@ static void drive_backup_prepare(BlkTransactionState 
*common, Error **errp)
                       backup->sync,
                       backup->has_mode, backup->mode,
                       backup->has_speed, backup->speed,
+                     backup->has_bitmap, backup->bitmap,
                       backup->has_on_source_error, backup->on_source_error,
                       backup->has_on_target_error, backup->on_target_error,
                       &local_err);
@@ -2358,6 +2359,7 @@ void qmp_drive_backup(const char *device, const char 
*target,
                        enum MirrorSyncMode sync,
                        bool has_mode, enum NewImageMode mode,
                        bool has_speed, int64_t speed,
+                      bool has_bitmap, const char *bitmap,
                        bool has_on_source_error, BlockdevOnError 
on_source_error,
                        bool has_on_target_error, BlockdevOnError 
on_target_error,
                        Error **errp)
@@ -2365,6 +2367,7 @@ void qmp_drive_backup(const char *device, const char 
*target,
      BlockDriverState *bs;
      BlockDriverState *target_bs;
      BlockDriverState *source = NULL;
+    BdrvDirtyBitmap *bmap = NULL;
      AioContext *aio_context;
      BlockDriver *drv = NULL;
      Error *local_err = NULL;
@@ -2460,7 +2463,16 @@ void qmp_drive_backup(const char *device, const char 
*target,

      bdrv_set_aio_context(target_bs, aio_context);

-    backup_start(bs, target_bs, speed, sync, on_source_error, on_target_error,
+    if (has_bitmap) {
+        bmap = bdrv_find_dirty_bitmap(bs, bitmap);
+        if (!bmap) {
+            error_setg(errp, "Bitmap '%s' could not be found", bitmap);
+            goto out;
+        }
+    }
+
+    backup_start(bs, target_bs, speed, sync, bmap,
+                 on_source_error, on_target_error,
                   block_job_cb, bs, &local_err);
      if (local_err != NULL) {
          bdrv_unref(target_bs);
diff --git a/hmp.c b/hmp.c
index 481be80..63b19c7 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1021,7 +1021,8 @@ void hmp_drive_backup(Monitor *mon, const QDict *qdict)

      qmp_drive_backup(device, filename, !!format, format,
                       full ? MIRROR_SYNC_MODE_FULL : MIRROR_SYNC_MODE_TOP,
-                     true, mode, false, 0, false, 0, false, 0, &err);
+                     true, mode, false, 0, false, NULL,
+                     false, 0, false, 0, &err);
      hmp_handle_error(mon, &err);
  }

diff --git a/include/block/block.h b/include/block/block.h
index 6138544..99ed679 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -462,6 +462,7 @@ void bdrv_reset_dirty_bitmap(BlockDriverState *bs, 
BdrvDirtyBitmap *bitmap,
  void bdrv_clear_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap);
  void bdrv_dirty_iter_init(BlockDriverState *bs,
                            BdrvDirtyBitmap *bitmap, struct HBitmapIter *hbi);
+void bdrv_set_dirty_iter(struct HBitmapIter *hbi, int64_t offset);
  int64_t bdrv_get_dirty_count(BlockDriverState *bs, BdrvDirtyBitmap *bitmap);

  void bdrv_enable_copy_on_read(BlockDriverState *bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 06a21dd..cb1e4a1 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -584,6 +584,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
   * @target: Block device to write to.
   * @speed: The maximum speed, in bytes per second, or 0 for unlimited.
   * @sync_mode: What parts of the disk image should be copied to the 
destination.
+ * @sync_bitmap: The dirty bitmap if sync_mode is 
MIRROR_SYNC_MODE_DIRTY_BITMAP.
   * @on_source_error: The action to take upon error reading from the source.
   * @on_target_error: The action to take upon error writing to the target.
   * @cb: Completion function for the job.
@@ -594,6 +595,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
   */
  void backup_start(BlockDriverState *bs, BlockDriverState *target,
                    int64_t speed, MirrorSyncMode sync_mode,
+                  BdrvDirtyBitmap *sync_bitmap,
                    BlockdevOnError on_source_error,
                    BlockdevOnError on_target_error,
                    BlockCompletionFunc *cb, void *opaque,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 3e863b9..92c3a84 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -500,7 +500,7 @@
  # Since: 1.3
  ##
  { 'enum': 'MirrorSyncMode',
-  'data': ['top', 'full', 'none'] }
+  'data': ['top', 'full', 'none', 'dirty-bitmap'] }


Maybe document version info for 'dirty-bitmap'? Eric?

Fam

<snip>



Thanks!
--John
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