[Qemu-devel] [PATCH 03/12] block: Introduce BlockBackendPublic

[Kevin Wolf <kwolf@redhat.com>]

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 <kwolf@redhat.com>
---
 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;
 
     void *dev;                  /* attached device model, if any */
     /* TODO change to DeviceState when all users are qdevified */
@@ -410,6 +411,22 @@ BlockBackend *blk_by_legacy_dinfo(DriveInfo *dinfo)
 }
 
 /*
+ * Returns a pointer to the publicly accessible fields of @blk.
+ */
+BlockBackendPublic *blk_get_public(BlockBackend *blk)
+{
+    return &blk->public;
+}
+
+/*
+ * Returns a BlockBackend given the associated @public fields.
+ */
+BlockBackend *blk_by_public(BlockBackendPublic *public)
+{
+    return container_of(public, BlockBackend, public);
+}
+
+/*
  * Disassociates the currently associated BlockDriverState from @blk.
  */
 void blk_remove_bs(BlockBackend *blk)
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index d839bff..bb4ff6f 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -59,6 +59,12 @@ typedef struct BlockDevOps {
     void (*resize_cb)(void *opaque);
 } BlockDevOps;
 
+/* 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;
+
 BlockBackend *blk_new(Error **errp);
 BlockBackend *blk_new_with_bs(Error **errp);
 BlockBackend *blk_new_open(const char *filename, const char *reference,
@@ -74,6 +80,9 @@ BlockDriverState *blk_next_root_bs(BlockDriverState *bs);
 bool monitor_add_blk(BlockBackend *blk, const char *name, Error **errp);
 void monitor_remove_blk(BlockBackend *blk);
 
+BlockBackendPublic *blk_get_public(BlockBackend *blk);
+BlockBackend *blk_by_public(BlockBackendPublic *public);
+
 BlockDriverState *blk_bs(BlockBackend *blk);
 void blk_remove_bs(BlockBackend *blk);
 void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs);
-- 
1.8.3.1