Re: [Qemu-devel] [PATCH] block: Make op blockers recursive

[Benoît Canet]

On Mon, Aug 25, 2014 at 02:04:24PM +0800, Fam Zheng wrote:
> On Fri, 08/22 18:11, Benoît Canet wrote:
> > Since the block layer code is starting to modify the BDS graph right in the
> > middle of BDS chains (block-mirror's replace parameter for example) QEMU 
> > needs
> > to properly block and unblock whole BDS subtrees; recursion is a neat way to
> > achieve this task.
> > 
> > This patch also takes care of modifying the op blockers users.
> 
> Is this going to replace backing_blocker?
> 
> I think it is too general an approach to control the operation properly,
> because the op blocker may not work in the same way for all types of BDS
> connections.  In other words, the choosing of op blockers are likely
> conditional on graph edge types, that's why backing_blocker was added here. 
> For
> example, A VMDK extent connection will probably need a different set of
> blockers than bs->file connection.
> 
> So could you explain in which cases is the recursive blocking/unblocking
> useful?

It's designed for the new crop of block operations operating on BDS located in
the middle of the backing chain: Jeff's patches, intermediate live streaming or
intermediate mirroring.
Recursively blocking BDS allows to do these operations safely.

Best regards

Benoît


> 
> Fam
> 
> > 
> > Signed-off-by: Benoit Canet <address@hidden>
> > ---
> >  block.c                   | 69 
> > ++++++++++++++++++++++++++++++++++++++++++++---
> >  block/blkverify.c         | 21 +++++++++++++++
> >  block/commit.c            |  3 +++
> >  block/mirror.c            | 17 ++++++++----
> >  block/quorum.c            | 25 +++++++++++++++++
> >  block/stream.c            |  3 +++
> >  block/vmdk.c              | 34 +++++++++++++++++++++++
> >  include/block/block.h     |  2 +-
> >  include/block/block_int.h |  6 +++++
> >  9 files changed, 171 insertions(+), 9 deletions(-)
> > 
> > diff --git a/block.c b/block.c
> > index 6fa0201..d964b6c 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -5446,7 +5446,9 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, 
> > BlockOpType op, Error **errp)
> >      return false;
> >  }
> >  
> > -void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
> > +/* do the real work of blocking a BDS */
> > +static void bdrv_do_op_block(BlockDriverState *bs, BlockOpType op,
> > +                             Error *reason)
> >  {
> >      BdrvOpBlocker *blocker;
> >      assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> > @@ -5456,7 +5458,9 @@ void bdrv_op_block(BlockDriverState *bs, BlockOpType 
> > op, Error *reason)
> >      QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
> >  }
> >  
> > -void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
> > +/* do the real work of unblocking a BDS */
> > +static void bdrv_do_op_unblock(BlockDriverState *bs, BlockOpType op,
> > +                               Error *reason)
> >  {
> >      BdrvOpBlocker *blocker, *next;
> >      assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> > @@ -5468,6 +5472,65 @@ void bdrv_op_unblock(BlockDriverState *bs, 
> > BlockOpType op, Error *reason)
> >      }
> >  }
> >  
> > +static bool bdrv_op_is_blocked_by(BlockDriverState *bs, BlockOpType op,
> > +                                  Error *reason)
> > +{
> > +    BdrvOpBlocker *blocker, *next;
> > +    assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> > +    QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
> > +        if (blocker->reason == reason) {
> > +            return true;
> > +        }
> > +    }
> > +    return false;
> > +}
> > +
> > +/* block recursively a BDS */
> > +void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
> > +{
> > +    if (!bs) {
> > +        return;
> > +    }
> > +
> > +    /* prevent recursion loop */
> > +    if (bdrv_op_is_blocked_by(bs, op, reason)) {
> > +        return;
> > +    }
> > +
> > +    /* block first for recursion loop protection to work */
> > +    bdrv_do_op_block(bs, op, reason);
> > +
> > +    bdrv_op_block(bs->file, op, reason);
> > +    bdrv_op_block(bs->backing_hd, op, reason);
> > +
> > +    if (bs->drv && bs->drv->bdrv_op_recursive_block) {
> > +        bs->drv->bdrv_op_recursive_block(bs, op, reason);
> > +    }
> > +}
> > +
> > +/* unblock recursively a BDS */
> > +void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
> > +{
> > +    if (!bs) {
> > +        return;
> > +    }
> > +
> > +    /* prevent recursion loop */
> > +    if (!bdrv_op_is_blocked_by(bs, op, reason)) {
> > +        return;
> > +    }
> > +
> > +    /* unblock first for recursion loop protection to work */
> > +    bdrv_do_op_unblock(bs, op, reason);
> > +
> > +    bdrv_op_unblock(bs->file, op, reason);
> > +    bdrv_op_unblock(bs->backing_hd, op, reason);
> > +
> > +    if (bs->drv && bs->drv->bdrv_op_recursive_unblock) {
> > +        bs->drv->bdrv_op_recursive_unblock(bs, op, reason);
> > +    }
> > +}
> > +
> >  void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
> >  {
> >      int i;
> > @@ -5848,7 +5911,7 @@ BlockDriverState *check_to_replace_node(const char 
> > *node_name, Error **errp)
> >          return NULL;
> >      }
> >  
> > -    if (bdrv_op_is_blocked(to_replace_bs, BLOCK_OP_TYPE_REPLACE, errp)) {
> > +    if (bdrv_op_is_blocked(to_replace_bs, BLOCK_OP_TYPE_MIRROR_REPLACE, 
> > errp)) {
> >          return NULL;
> >      }
> >  
> > diff --git a/block/blkverify.c b/block/blkverify.c
> > index 621b785..75ec3df 100644
> > --- a/block/blkverify.c
> > +++ b/block/blkverify.c
> > @@ -320,6 +320,24 @@ static void 
> > blkverify_attach_aio_context(BlockDriverState *bs,
> >      bdrv_attach_aio_context(s->test_file, new_context);
> >  }
> >  
> > +static void blkverify_op_recursive_block(BlockDriverState *bs, BlockOpType 
> > op,
> > +                                         Error *reason)
> > +{
> > +    BDRVBlkverifyState *s = bs->opaque;
> > +
> > +    bdrv_op_block(bs->file, op, reason);
> > +    bdrv_op_block(s->test_file, op, reason);
> > +}
> > +
> > +static void blkverify_op_recursive_unblock(BlockDriverState *bs, 
> > BlockOpType op,
> > +                                           Error *reason)
> > +{
> > +    BDRVBlkverifyState *s = bs->opaque;
> > +
> > +    bdrv_op_unblock(bs->file, op, reason);
> > +    bdrv_op_unblock(s->test_file, op, reason);
> > +}
> > +
> >  static BlockDriver bdrv_blkverify = {
> >      .format_name                      = "blkverify",
> >      .protocol_name                    = "blkverify",
> > @@ -337,6 +355,9 @@ static BlockDriver bdrv_blkverify = {
> >      .bdrv_attach_aio_context          = blkverify_attach_aio_context,
> >      .bdrv_detach_aio_context          = blkverify_detach_aio_context,
> >  
> > +    .bdrv_op_recursive_block          = blkverify_op_recursive_block,
> > +    .bdrv_op_recursive_unblock        = blkverify_op_recursive_unblock,
> > +
> >      .is_filter                        = true,
> >      .bdrv_recurse_is_first_non_filter = 
> > blkverify_recurse_is_first_non_filter,
> >  };
> > diff --git a/block/commit.c b/block/commit.c
> > index 91517d3..8a122b7 100644
> > --- a/block/commit.c
> > +++ b/block/commit.c
> > @@ -142,6 +142,9 @@ wait:
> >  
> >      if (!block_job_is_cancelled(&s->common) && sector_num == end) {
> >          /* success */
> > +        /* unblock only BDS to be dropped */
> > +        bdrv_op_unblock_all(top, s->common.blocker);
> > +        bdrv_op_block_all(base, s->common.blocker);
> >          ret = bdrv_drop_intermediate(active, top, base, 
> > s->backing_file_str);
> >      }
> >  
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 5e7a166..28ed47d 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -324,6 +324,7 @@ static void coroutine_fn mirror_run(void *opaque)
> >      uint64_t last_pause_ns;
> >      BlockDriverInfo bdi;
> >      char backing_filename[1024];
> > +    BlockDriverState *to_replace;
> >      int ret = 0;
> >      int n;
> >  
> > @@ -512,14 +513,16 @@ immediate_exit:
> >      g_free(s->in_flight_bitmap);
> >      bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
> >      bdrv_iostatus_disable(s->target);
> > +    to_replace = s->common.bs;
> > +    if (s->to_replace) {
> > +        bdrv_op_unblock_all(s->to_replace, s->replace_blocker);
> > +        to_replace = s->to_replace;
> > +    }
> >      if (s->should_complete && ret == 0) {
> > -        BlockDriverState *to_replace = s->common.bs;
> > -        if (s->to_replace) {
> > -            to_replace = s->to_replace;
> > -        }
> >          if (bdrv_get_flags(s->target) != bdrv_get_flags(to_replace)) {
> >              bdrv_reopen(s->target, bdrv_get_flags(to_replace), NULL);
> >          }
> > +        bdrv_op_unblock_all(to_replace, bs->job->blocker);
> >          bdrv_swap(s->target, to_replace);
> >          if (s->common.driver->job_type == BLOCK_JOB_TYPE_COMMIT) {
> >              /* drop the bs loop chain formed by the swap: break the loop 
> > then
> > @@ -530,7 +533,6 @@ immediate_exit:
> >          }
> >      }
> >      if (s->to_replace) {
> > -        bdrv_op_unblock_all(s->to_replace, s->replace_blocker);
> >          error_free(s->replace_blocker);
> >          bdrv_unref(s->to_replace);
> >      }
> > @@ -648,6 +650,11 @@ static void mirror_start_job(BlockDriverState *bs, 
> > BlockDriverState *target,
> >          return;
> >      }
> >  
> > +    /* remove BLOCK_OP_TYPE_MIRROR_REPLACE from the list of
> > +     * blocked operations so the replaces parameter can work
> > +     */
> > +    bdrv_op_unblock(bs, BLOCK_OP_TYPE_MIRROR_REPLACE, bs->job->blocker);
> > +
> >      s->replaces = g_strdup(replaces);
> >      s->on_source_error = on_source_error;
> >      s->on_target_error = on_target_error;
> > diff --git a/block/quorum.c b/block/quorum.c
> > index d5ee9c0..c260171 100644
> > --- a/block/quorum.c
> > +++ b/block/quorum.c
> > @@ -945,6 +945,28 @@ static void quorum_attach_aio_context(BlockDriverState 
> > *bs,
> >      }
> >  }
> >  
> > +static void quorum_op_recursive_block(BlockDriverState *bs, BlockOpType op,
> > +                                      Error *reason)
> > +{
> > +    BDRVQuorumState *s = bs->opaque;
> > +    int i;
> > +
> > +    for (i = 0; i < s->num_children; i++) {
> > +        bdrv_op_block(s->bs[i], op, reason);
> > +    }
> > +}
> > +
> > +static void quorum_op_recursive_unblock(BlockDriverState *bs, BlockOpType 
> > op,
> > +                                        Error *reason)
> > +{
> > +    BDRVQuorumState *s = bs->opaque;
> > +    int i;
> > +
> > +    for (i = 0; i < s->num_children; i++) {
> > +        bdrv_op_unblock(s->bs[i], op, reason);
> > +    }
> > +}
> > +
> >  static BlockDriver bdrv_quorum = {
> >      .format_name                        = "quorum",
> >      .protocol_name                      = "quorum",
> > @@ -965,6 +987,9 @@ static BlockDriver bdrv_quorum = {
> >      .bdrv_detach_aio_context            = quorum_detach_aio_context,
> >      .bdrv_attach_aio_context            = quorum_attach_aio_context,
> >  
> > +    .bdrv_op_recursive_block            = quorum_op_recursive_block,
> > +    .bdrv_op_recursive_unblock          = quorum_op_recursive_unblock,
> > +
> >      .is_filter                          = true,
> >      .bdrv_recurse_is_first_non_filter   = 
> > quorum_recurse_is_first_non_filter,
> >  };
> > diff --git a/block/stream.c b/block/stream.c
> > index cdea3e8..2c917b7 100644
> > --- a/block/stream.c
> > +++ b/block/stream.c
> > @@ -192,6 +192,9 @@ wait:
> >              }
> >          }
> >          ret = bdrv_change_backing_file(bs, base_id, base_fmt);
> > +        /* unblock only BDS to be dropped */
> > +        bdrv_op_unblock_all(bs->backing_hd, s->common.blocker);
> > +        bdrv_op_block_all(base, s->common.blocker);
> >          close_unused_images(bs, base, base_id);
> >      }
> >  
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index 01412a8..bc5b17f 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -2220,6 +2220,38 @@ static QemuOptsList vmdk_create_opts = {
> >      }
> >  };
> >  
> > +static void vmdk_op_recursive_block(BlockDriverState *bs, BlockOpType op,
> > +                                      Error *reason)
> > +{
> > +    BDRVVmdkState *s = bs->opaque;
> > +    int i;
> > +
> > +    bdrv_op_block(bs->file, op, reason);
> > +    bdrv_op_block(bs->backing_hd, op, reason);
> > +
> > +    for (i = 0; i < s->num_extents; i++) {
> > +        if (s->extents[i].file) {
> > +            bdrv_op_block(s->extents[i].file, op, reason);
> > +        }
> > +    }
> > +}
> > +
> > +static void vmdk_op_recursive_unblock(BlockDriverState *bs, BlockOpType op,
> > +                                        Error *reason)
> > +{
> > +    BDRVVmdkState *s = bs->opaque;
> > +    int i;
> > +
> > +    bdrv_op_unblock(bs->file, op, reason);
> > +    bdrv_op_unblock(bs->backing_hd, op, reason);
> > +
> > +    for (i = 0; i < s->num_extents; i++) {
> > +        if (s->extents[i].file) {
> > +            bdrv_op_unblock(s->extents[i].file, op, reason);
> > +        }
> > +    }
> > +}
> > +
> >  static BlockDriver bdrv_vmdk = {
> >      .format_name                  = "vmdk",
> >      .instance_size                = sizeof(BDRVVmdkState),
> > @@ -2242,6 +2274,8 @@ static BlockDriver bdrv_vmdk = {
> >      .bdrv_get_info                = vmdk_get_info,
> >      .bdrv_detach_aio_context      = vmdk_detach_aio_context,
> >      .bdrv_attach_aio_context      = vmdk_attach_aio_context,
> > +    .bdrv_op_recursive_block      = vmdk_op_recursive_block,
> > +    .bdrv_op_recursive_unblock    = vmdk_op_recursive_unblock,
> >  
> >      .supports_backing             = true,
> >      .create_opts                  = &vmdk_create_opts,
> > diff --git a/include/block/block.h b/include/block/block.h
> > index e94b701..4729a0a 100644
> > --- a/include/block/block.h
> > +++ b/include/block/block.h
> > @@ -175,7 +175,7 @@ typedef enum BlockOpType {
> >      BLOCK_OP_TYPE_MIRROR,
> >      BLOCK_OP_TYPE_RESIZE,
> >      BLOCK_OP_TYPE_STREAM,
> > -    BLOCK_OP_TYPE_REPLACE,
> > +    BLOCK_OP_TYPE_MIRROR_REPLACE,
> >      BLOCK_OP_TYPE_MAX,
> >  } BlockOpType;
> >  
> > diff --git a/include/block/block_int.h b/include/block/block_int.h
> > index 7b541a0..a802abc 100644
> > --- a/include/block/block_int.h
> > +++ b/include/block/block_int.h
> > @@ -266,6 +266,12 @@ struct BlockDriver {
> >      void (*bdrv_io_unplug)(BlockDriverState *bs);
> >      void (*bdrv_flush_io_queue)(BlockDriverState *bs);
> >  
> > +    /* helps blockers to propagate recursively */
> > +    void (*bdrv_op_recursive_block)(BlockDriverState *bs, BlockOpType op,
> > +                                    Error *reason);
> > +    void (*bdrv_op_recursive_unblock)(BlockDriverState *bs, BlockOpType op,
> > +                                      Error *reason);
> > +
> >      QLIST_ENTRY(BlockDriver) list;
> >  };
> >  
> > -- 
> > 2.1.0
> >