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authorStefan Hajnoczi <stefanha@redhat.com>2014-10-21 12:03:54 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2014-11-03 11:41:49 +0000
commitdec7d421f85578b0949292336f784f55ac84812d (patch)
tree1e3c37516831a97591874685d13f270e8cb7a2d5
parent723c5d93c51bdb3adbc238ce90195c0864aa6cd5 (diff)
blockjob: add block_job_defer_to_main_loop()
Block jobs will run in the BlockDriverState's AioContext, which may not always be the QEMU main loop. There are some block layer APIs that are either not thread-safe or risk lock ordering problems. This includes bdrv_unref(), bdrv_close(), and anything that calls bdrv_drain_all(). The block_job_defer_to_main_loop() API allows a block job to schedule a function to run in the main loop with the BlockDriverState AioContext held. This function will be used to perform cleanup and backing chain manipulations in block jobs. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-id: 1413889440-32577-6-git-send-email-stefanha@redhat.com
-rw-r--r--blockjob.c45
-rw-r--r--include/block/blockjob.h19
2 files changed, 64 insertions, 0 deletions
diff --git a/blockjob.c b/blockjob.c
index 448b9ce113..cd4b573adb 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -342,3 +342,48 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockDriverState *bs,
}
return action;
}
+
+typedef struct {
+ BlockJob *job;
+ QEMUBH *bh;
+ AioContext *aio_context;
+ BlockJobDeferToMainLoopFn *fn;
+ void *opaque;
+} BlockJobDeferToMainLoopData;
+
+static void block_job_defer_to_main_loop_bh(void *opaque)
+{
+ BlockJobDeferToMainLoopData *data = opaque;
+ AioContext *aio_context;
+
+ qemu_bh_delete(data->bh);
+
+ /* Prevent race with block_job_defer_to_main_loop() */
+ aio_context_acquire(data->aio_context);
+
+ /* Fetch BDS AioContext again, in case it has changed */
+ aio_context = bdrv_get_aio_context(data->job->bs);
+ aio_context_acquire(aio_context);
+
+ data->fn(data->job, data->opaque);
+
+ aio_context_release(aio_context);
+
+ aio_context_release(data->aio_context);
+
+ g_free(data);
+}
+
+void block_job_defer_to_main_loop(BlockJob *job,
+ BlockJobDeferToMainLoopFn *fn,
+ void *opaque)
+{
+ BlockJobDeferToMainLoopData *data = g_malloc(sizeof(*data));
+ data->job = job;
+ data->bh = qemu_bh_new(block_job_defer_to_main_loop_bh, data);
+ data->aio_context = bdrv_get_aio_context(job->bs);
+ data->fn = fn;
+ data->opaque = opaque;
+
+ qemu_bh_schedule(data->bh);
+}
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 9694f130b0..b6d4ebbe03 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -315,4 +315,23 @@ void block_job_iostatus_reset(BlockJob *job);
BlockErrorAction block_job_error_action(BlockJob *job, BlockDriverState *bs,
BlockdevOnError on_err,
int is_read, int error);
+
+typedef void BlockJobDeferToMainLoopFn(BlockJob *job, void *opaque);
+
+/**
+ * block_job_defer_to_main_loop:
+ * @job: The job
+ * @fn: The function to run in the main loop
+ * @opaque: The opaque value that is passed to @fn
+ *
+ * Execute a given function in the main loop with the BlockDriverState
+ * AioContext acquired. Block jobs must call bdrv_unref(), bdrv_close(), and
+ * anything that uses bdrv_drain_all() in the main loop.
+ *
+ * The @job AioContext is held while @fn executes.
+ */
+void block_job_defer_to_main_loop(BlockJob *job,
+ BlockJobDeferToMainLoopFn *fn,
+ void *opaque);
+
#endif