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Re: [PATCH v4 02/25] include/block/block: split header into I/O and glob

From: Hanna Reitz
Subject: Re: [PATCH v4 02/25] include/block/block: split header into I/O and global state API
Date: Thu, 11 Nov 2021 16:00:26 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0

On 25.10.21 12:17, Emanuele Giuseppe Esposito wrote:
block.h currently contains a mix of functions:
some of them run under the BQL and modify the block layer graph,
others are instead thread-safe and perform I/O in iothreads.
It is not easy to understand which function is part of which
group (I/O vs GS), and this patch aims to clarify it.

The "GS" functions need the BQL, and often use
aio_context_acquire/release and/or drain to be sure they
can modify the graph safely.
The I/O function are instead thread safe, and can run in
any AioContext.

By splitting the header in two files, block-io.h
and block-global-state.h we have a clearer view on what
needs what kind of protection. block-common.h
contains common structures shared by both headers.

block.h is left there for legacy and to avoid changing
all includes in all c files that use the block APIs.

Assertions are added in the next patch.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
  block.c                            |   3 +
  block/meson.build                  |   7 +-
  include/block/block-common.h       | 389 +++++++++++++
  include/block/block-global-state.h | 286 ++++++++++
  include/block/block-io.h           | 306 ++++++++++
  include/block/block.h              | 878 +----------------------------
  6 files changed, 1012 insertions(+), 857 deletions(-)
  create mode 100644 include/block/block-common.h
  create mode 100644 include/block/block-global-state.h
  create mode 100644 include/block/block-io.h


diff --git a/include/block/block-io.h b/include/block/block-io.h
new file mode 100644
index 0000000000..9af4609ccb
--- /dev/null
+++ b/include/block/block-io.h


+ * I/O API functions. These functions are thread-safe, and therefore
+ * can run in any thread as long as the thread has called
+ * aio_context_acquire/release().
+ */
+int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs,
+                          Error **errp);

Why is this function here?  Naïvely, I would’ve assumed as a graph-modifying function it should be in block-global-state.h.

I mean, perhaps it’s thread-safe and then it can fit here, too. Still, it surprises me a bit to find this here.


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