block: remove AIOCBInfo->get_aio_context()

The synchronous bdrv_aio_cancel() function needs the acb's AioContext so
it can call aio_poll() to wait for cancellation.

It turns out that all users run under the BQL in the main AioContext, so
this callback is not needed.

Remove the callback, mark bdrv_aio_cancel() GLOBAL_STATE_CODE just like
its blk_aio_cancel() caller, and poll the main loop AioContext.

The purpose of this cleanup is to identify bdrv_aio_cancel() as an API
that does not work with the multi-queue block layer.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230912231037.826804-2-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -33,8 +33,6 @@
 
 #define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
 
-static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb);
-
 typedef struct BlockBackendAioNotifier {
     void (*attached_aio_context)(AioContext *new_context, void *opaque);
     void (*detach_aio_context)(void *opaque);
@@ -103,7 +101,6 @@ typedef struct BlockBackendAIOCB {
 } BlockBackendAIOCB;
 
 static const AIOCBInfo block_backend_aiocb_info = {
-    .get_aio_context = blk_aiocb_get_aio_context,
     .aiocb_size = sizeof(BlockBackendAIOCB),
 };
 
@@ -1562,16 +1559,8 @@ typedef struct BlkAioEmAIOCB {
     bool has_returned;
 } BlkAioEmAIOCB;
 
-static AioContext *blk_aio_em_aiocb_get_aio_context(BlockAIOCB *acb_)
-{
-    BlkAioEmAIOCB *acb = container_of(acb_, BlkAioEmAIOCB, common);
-
-    return blk_get_aio_context(acb->rwco.blk);
-}
-
 static const AIOCBInfo blk_aio_em_aiocb_info = {
     .aiocb_size         = sizeof(BlkAioEmAIOCB),
-    .get_aio_context    = blk_aio_em_aiocb_get_aio_context,
 };
 
 static void blk_aio_complete(BlkAioEmAIOCB *acb)
@@ -2451,12 +2440,6 @@ AioContext *blk_get_aio_context(BlockBackend *blk)
     return blk->ctx;
 }
 
-static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb)
-{
-    BlockBackendAIOCB *blk_acb = DO_UPCAST(BlockBackendAIOCB, common, acb);
-    return blk_get_aio_context(blk_acb->blk);
-}
-
 int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
                         Error **errp)
 {

block/io.c

@@ -2950,25 +2950,18 @@ int bdrv_load_vmstate(BlockDriverState *bs, uint8_t *buf,
 /**************************************************************/
 /* async I/Os */
 
+/**
+ * Synchronously cancels an acb. Must be called with the BQL held and the acb
+ * must be processed with the BQL held too (IOThreads are not allowed).
+ *
+ * Use bdrv_aio_cancel_async() instead when possible.
+ */
 void bdrv_aio_cancel(BlockAIOCB *acb)
 {
-    IO_CODE();
+    GLOBAL_STATE_CODE();
     qemu_aio_ref(acb);
     bdrv_aio_cancel_async(acb);
-    while (acb->refcnt > 1) {
-        if (acb->aiocb_info->get_aio_context) {
-            aio_poll(acb->aiocb_info->get_aio_context(acb), true);
-        } else if (acb->bs) {
-            /* qemu_aio_ref and qemu_aio_unref are not thread-safe, so
-             * assert that we're not using an I/O thread.  Thread-safe
-             * code should use bdrv_aio_cancel_async exclusively.
-             */
-            assert(bdrv_get_aio_context(acb->bs) == qemu_get_aio_context());
-            aio_poll(bdrv_get_aio_context(acb->bs), true);
-        } else {
-            abort();
-        }
-    }
+    AIO_WAIT_WHILE_UNLOCKED(NULL, acb->refcnt > 1);
     qemu_aio_unref(acb);
 }
 

hw/nvme/ctrl.c

@@ -2130,11 +2130,6 @@ static inline bool nvme_is_write(NvmeRequest *req)
            rw->opcode == NVME_CMD_WRITE_ZEROES;
 }
 
-static AioContext *nvme_get_aio_context(BlockAIOCB *acb)
-{
-    return qemu_get_aio_context();
-}
-
 static void nvme_misc_cb(void *opaque, int ret)
 {
     NvmeRequest *req = opaque;
@@ -3302,7 +3297,6 @@ static void nvme_flush_cancel(BlockAIOCB *acb)
 static const AIOCBInfo nvme_flush_aiocb_info = {
     .aiocb_size = sizeof(NvmeFlushAIOCB),
     .cancel_async = nvme_flush_cancel,
-    .get_aio_context = nvme_get_aio_context,
 };
 
 static void nvme_do_flush(NvmeFlushAIOCB *iocb);
@@ -6478,7 +6472,6 @@ static void nvme_format_cancel(BlockAIOCB *aiocb)
 static const AIOCBInfo nvme_format_aiocb_info = {
     .aiocb_size = sizeof(NvmeFormatAIOCB),
     .cancel_async = nvme_format_cancel,
-    .get_aio_context = nvme_get_aio_context,
 };
 
 static void nvme_format_set(NvmeNamespace *ns, uint8_t lbaf, uint8_t mset,

include/block/aio.h

@@ -31,7 +31,6 @@ typedef void BlockCompletionFunc(void *opaque, int ret);
 
 typedef struct AIOCBInfo {
     void (*cancel_async)(BlockAIOCB *acb);
-    AioContext *(*get_aio_context)(BlockAIOCB *acb);
     size_t aiocb_size;
 } AIOCBInfo;
 

include/block/block-global-state.h

@@ -185,6 +185,8 @@ void bdrv_drain_all_begin_nopoll(void);
 void bdrv_drain_all_end(void);
 void bdrv_drain_all(void);
 
+void bdrv_aio_cancel(BlockAIOCB *acb);
+
 int bdrv_has_zero_init_1(BlockDriverState *bs);
 int bdrv_has_zero_init(BlockDriverState *bs);
 BlockDriverState *bdrv_find_node(const char *node_name);

include/block/block-io.h

@@ -101,7 +101,6 @@ bdrv_co_delete_file_noerr(BlockDriverState *bs);
 
 
 /* async block I/O */
-void bdrv_aio_cancel(BlockAIOCB *acb);
 void bdrv_aio_cancel_async(BlockAIOCB *acb);
 
 /* sg packet commands */

softmmu/dma-helpers.c

@@ -206,17 +206,9 @@ static void dma_aio_cancel(BlockAIOCB *acb)
     }
 }
 
-static AioContext *dma_get_aio_context(BlockAIOCB *acb)
-{
-    DMAAIOCB *dbs = container_of(acb, DMAAIOCB, common);
-
-    return dbs->ctx;
-}
-
 static const AIOCBInfo dma_aiocb_info = {
     .aiocb_size         = sizeof(DMAAIOCB),
     .cancel_async       = dma_aio_cancel,
-    .get_aio_context    = dma_get_aio_context,
 };
 
 BlockAIOCB *dma_blk_io(AioContext *ctx,

util/thread-pool.c

@@ -228,17 +228,9 @@ static void thread_pool_cancel(BlockAIOCB *acb)
 
 }
 
-static AioContext *thread_pool_get_aio_context(BlockAIOCB *acb)
-{
-    ThreadPoolElement *elem = (ThreadPoolElement *)acb;
-    ThreadPool *pool = elem->pool;
-    return pool->ctx;
-}
-
 static const AIOCBInfo thread_pool_aiocb_info = {
     .aiocb_size         = sizeof(ThreadPoolElement),
     .cancel_async       = thread_pool_cancel,
-    .get_aio_context    = thread_pool_get_aio_context,
 };
 
 BlockAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,