Re: [RFC PATCH v2 13/25] include/systemu/blockdev.h: global state API

[Stefan Hajnoczi]

On Tue, Oct 05, 2021 at 10:32:03AM -0400, Emanuele Giuseppe Esposito wrote:
> blockdev functions run always under the BQL lock.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  include/sysemu/blockdev.h | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/include/sysemu/blockdev.h b/include/sysemu/blockdev.h
> index 32c2d6023c..28233f6b63 100644
> --- a/include/sysemu/blockdev.h
> +++ b/include/sysemu/blockdev.h
> @@ -38,24 +38,49 @@ struct DriveInfo {
>      QTAILQ_ENTRY(DriveInfo) next;
>  };
>  
> -DriveInfo *blk_legacy_dinfo(BlockBackend *blk);
> +/*
> + * Global state (GS) API. These functions run under the BQL lock.
> + *
> + * If a function modifies the graph, it also uses drain and/or
> + * aio_context_acquire/release to be sure it has unique access.
> + * aio_context locking is needed together with BQL because of
> + * the thread-safe I/O API that concurrently runs and accesses
> + * the graph without the BQL.
> + *
> + * It is important to note that not all of these functions are
> + * necessarily limited to running under the BQL, but they would
> + * require additional auditing and may small thread-safety changes
> + * to move them into the I/O API. Often it's not worth doing that
> + * work since the APIs are only used with the BQL held at the
> + * moment, so they have been placed in the GS API (for now).
> + *
> + * All functions in this header must use this assertion:
> + * g_assert(qemu_in_main_thread());
> + * to catch when they are accidentally called without the BQL.
> + */
> +
>  DriveInfo *blk_set_legacy_dinfo(BlockBackend *blk, DriveInfo *dinfo);
>  BlockBackend *blk_by_legacy_dinfo(DriveInfo *dinfo);
>  
>  void override_max_devs(BlockInterfaceType type, int max_devs);
>  
>  DriveInfo *drive_get(BlockInterfaceType type, int bus, int unit);
> -void drive_mark_claimed_by_board(void);

This function prototype is no longer used. Please make a note of this in
the commit description so reviewers know the deletion is intentional and
the reason for it. (It could have been an accident so I had to grep the
code to figure out why you did this.)

Otherwise:

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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