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Re: [Qemu-devel] [PATCH 03/12] block: Introduce BlockBackendPublic
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 03/12] block: Introduce BlockBackendPublic |
Date: |
Tue, 22 Mar 2016 15:53:50 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
On 03/22/2016 09:33 AM, Kevin Wolf wrote:
> Some features, like I/O throttling, are implemented outside
> block-backend.c, but still want to keep BlockBackends in a list. In
> order to avoid exposing the whole struct layout in the public header
> file, this patch introduces an embedded public struct where list entry
> structs can be added and a pair of functions to convert between
> BlockBackend and BlockBackendPublic.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> block/block-backend.c | 17 +++++++++++++++++
> include/sysemu/block-backend.h | 9 +++++++++
> 2 files changed, 26 insertions(+)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index df8f717..4394950 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -33,6 +33,7 @@ struct BlockBackend {
> DriveInfo *legacy_dinfo; /* null unless created by drive_new() */
> QTAILQ_ENTRY(BlockBackend) link; /* for block_backends */
> QTAILQ_ENTRY(BlockBackend) monitor_link; /* for monitor_block_backends */
> + BlockBackendPublic public;
Any reason to not put the public struct at offset 0?
> +
> +/*
> + * Returns a BlockBackend given the associated @public fields.
> + */
> +BlockBackend *blk_by_public(BlockBackendPublic *public)
> +{
> + return container_of(public, BlockBackend, public);
> +}
At least container_of() doesn't care, so I guess it doesn't matter.
> +/* This struct is embedded in (the private) BlockBackend struct and contains
> + * fields that must be public. This is in particular for QLIST_ENTRY() and
> + * friends so that BlockBackends can be kept in lists outside
> block-backend.c */
> +typedef struct BlockBackendPublic {
> +} BlockBackendPublic;
No fields? So really all we need this for is so that we can have an
address of a member of the larger struct, so that we can do list
operations based on that address?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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[Qemu-devel] [PATCH 04/12] block: throttle-groups: Use BlockBackend pointers internally, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 08/12] block: Move I/O throttling configuration functions to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 11/12] block: Decouple throttling from BlockDriverState, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 05/12] block: Convert throttle_group_get_name() to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 07/12] block: Move actual I/O throttling to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 10/12] block: Drain throttling queue with BdrvChild callback, Kevin Wolf, 2016/03/22