diff mbox series

[RFC,3/4] include/sysemu/block-backend: split header into I/O and graph API

Message ID 20210908131021.774533-4-eesposit@redhat.com
State New
Headers show
Series block layer: split block APIs in graph and I/O | expand

Commit Message

Emanuele Giuseppe Esposito Sept. 8, 2021, 1:10 p.m. UTC 
block-backend.h currently contains a mix of functions:
some of them run under the BQL and modify the block layer graph,
others are instead thread-safe and perform I/O in iothreads.
It is not easy to understand which function is part of which
group (I/O vs graph), and this patch aims to clarify it.

The graph functions need the BQL, and often use
aio_context_acquire/release and/or drain to be sure they
can modify the graph safely.
The I/O function are instead thread safe, and can run in
any AioContext.

By splitting the header in two files, block-backend-io.h
and block-backend-graph.h we have a clearer view on what
needs what kind of protection. block-backend-common.h
instead contains common structures shared by both headers.

In addition, remove the block/block.h include as it seems
it is not necessary anymore, together with qemu/iov.h

block-backend.h is left there for legacy and avoid to change
all includes in all c files that use the block-backend APIs.

Assertions are added in the next patch.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/block-backend.c                 |   9 +-
 include/sysemu/block-backend-common.h |  74 ++++++++
 include/sysemu/block-backend-graph.h  | 132 +++++++++++++
 include/sysemu/block-backend-io.h     | 123 ++++++++++++
 include/sysemu/block-backend.h        | 262 +-------------------------
 5 files changed, 338 insertions(+), 262 deletions(-)
 create mode 100644 include/sysemu/block-backend-common.h
 create mode 100644 include/sysemu/block-backend-graph.h
 create mode 100644 include/sysemu/block-backend-io.h

Comments

Stefan Hajnoczi Sept. 13, 2021, 1:27 p.m. UTC | #1 
On Wed, Sep 08, 2021 at 09:10:20AM -0400, Emanuele Giuseppe Esposito wrote:
> diff --git a/include/sysemu/block-backend-graph.h b/include/sysemu/block-backend-graph.h
> new file mode 100644
> index 0000000000..3310987b16
> --- /dev/null
> +++ b/include/sysemu/block-backend-graph.h
> @@ -0,0 +1,132 @@
> +/*
> + * QEMU Block backends
> + *
> + * Copyright (C) 2014-2016 Red Hat, Inc.
> + *
> + * Authors:
> + *  Markus Armbruster <armbru@redhat.com>,
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.1
> + * or later.  See the COPYING.LIB file in the top-level directory.
> + */
> +
> +#ifndef BLOCK_BACKEND_GRAPH_H
> +#define BLOCK_BACKEND_GRAPH_H
> +
> +#include "block-backend-common.h"
> +
> +/*
> + * Graph API. These functions run under the BQL lock.
> + *
> + * If a function modifies the graph, it uses drain and/or
> + * aio_context_acquire/release to be sure it has unique access.

It's not obvious why additional locking is needed if the BQL is already
held. Please refer to the thread-safe I/O API functions that can be
running concurrently without the BQL.

> + *
> + * All functions in this header must use this assertion:
> + * g_assert(qemu_in_main_thread());
> + * to be sure they belong here.

I suggest "to catch when they are accidentally called without the BQL".
It explains the rationale whereas "to be sure they belong here" doesn't
explain anything.

> diff --git a/include/sysemu/block-backend-io.h b/include/sysemu/block-backend-io.h
> new file mode 100644
> index 0000000000..66a7bed9f0
> --- /dev/null
> +++ b/include/sysemu/block-backend-io.h
> @@ -0,0 +1,123 @@
> +/*
> + * QEMU Block backends
> + *
> + * Copyright (C) 2014-2016 Red Hat, Inc.
> + *
> + * Authors:
> + *  Markus Armbruster <armbru@redhat.com>,
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.1
> + * or later.  See the COPYING.LIB file in the top-level directory.
> + */
> +
> +#ifndef BLOCK_BACKEND_IO_H
> +#define BLOCK_BACKEND_IO_H
> +
> +#include "block-backend-common.h"
> +
> +/*
> + * I/O API functions. These functions are thread-safe, and therefore
> + * can run in any AioContext.

"can run in any AioContext" makes me wonder what the exact requirements
are. Can they run in any *thread* (regardless of whether an AioContext
even exists for that thread) or do they need to run in a thread that has
called qemu_set_current_aio_context()?
Stefan Hajnoczi Sept. 13, 2021, 1:41 p.m. UTC | #2 
On Wed, Sep 08, 2021 at 09:10:20AM -0400, Emanuele Giuseppe Esposito wrote:
> +/*
> + * Graph API. These functions run under the BQL lock.
> + *
> + * If a function modifies the graph, it uses drain and/or
> + * aio_context_acquire/release to be sure it has unique access.
> + *
> + * All functions in this header must use this assertion:
> + * g_assert(qemu_in_main_thread());
> + * to be sure they belong here.
> + */

It's 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 graph
API (for now).

Stefan
Paolo Bonzini Sept. 15, 2021, 12:14 p.m. UTC | #3 
On 13/09/21 15:27, Stefan Hajnoczi wrote:
>> +/*
>> + * I/O API functions. These functions are thread-safe, and therefore
>> + * can run in any AioContext.
> "can run in any AioContext" makes me wonder what the exact requirements
> are. Can they run in any*thread*  (regardless of whether an AioContext
> even exists for that thread) or do they need to run in a thread that has
> called qemu_set_current_aio_context()?

I think they can run in any thread as long as they have called 
aio_context_acquire/release; later on, they will be able to run in any 
thread completely (which will be the underlying mechanism for multiqueue).

Paolo
Stefan Hajnoczi Sept. 15, 2021, 2:38 p.m. UTC | #4 
On Wed, Sep 15, 2021 at 02:14:08PM +0200, Paolo Bonzini wrote:
> On 13/09/21 15:27, Stefan Hajnoczi wrote:
> > > +/*
> > > + * I/O API functions. These functions are thread-safe, and therefore
> > > + * can run in any AioContext.
> > "can run in any AioContext" makes me wonder what the exact requirements
> > are. Can they run in any*thread*  (regardless of whether an AioContext
> > even exists for that thread) or do they need to run in a thread that has
> > called qemu_set_current_aio_context()?
> 
> I think they can run in any thread as long as they have called
> aio_context_acquire/release; later on, they will be able to run in any
> thread completely (which will be the underlying mechanism for multiqueue).

Great, it would be good to reflect this in the comment.

Stefan
diff mbox series

Patch

diff --git a/block/block-backend.c b/block/block-backend.c
index deb55c272e..7d5216a9a0 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -78,6 +78,7 @@  struct BlockBackend {
     bool allow_aio_context_change;
     bool allow_write_beyond_eof;
 
+    /* Protected by BQL lock */
     NotifierList remove_bs_notifiers, insert_bs_notifiers;
     QLIST_HEAD(, BlockBackendAioNotifier) aio_notifiers;
 
@@ -110,12 +111,14 @@  static const AIOCBInfo block_backend_aiocb_info = {
 static void drive_info_del(DriveInfo *dinfo);
 static BlockBackend *bdrv_first_blk(BlockDriverState *bs);
 
-/* All BlockBackends */
+/* All BlockBackends. Protected by the BQL lock. */
 static QTAILQ_HEAD(, BlockBackend) block_backends =
     QTAILQ_HEAD_INITIALIZER(block_backends);
 
-/* All BlockBackends referenced by the monitor and which are iterated through by
- * blk_next() */
+/*
+ * All BlockBackends referenced by the monitor and which are iterated through by
+ * blk_next(). Protected by the BQL lock.
+ */
 static QTAILQ_HEAD(, BlockBackend) monitor_block_backends =
     QTAILQ_HEAD_INITIALIZER(monitor_block_backends);
 
diff --git a/include/sysemu/block-backend-common.h b/include/sysemu/block-backend-common.h
new file mode 100644
index 0000000000..52ff6a4d26
--- /dev/null
+++ b/include/sysemu/block-backend-common.h
@@ -0,0 +1,74 @@ 
+/*
+ * QEMU Block backends
+ *
+ * Copyright (C) 2014-2016 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@redhat.com>,
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#ifndef BLOCK_BACKEND_COMMON_H
+#define BLOCK_BACKEND_COMMON_H
+
+#include "block/throttle-groups.h"
+
+/* Callbacks for block device models */
+typedef struct BlockDevOps {
+    /*
+     * Runs when virtual media changed (monitor commands eject, change)
+     * Argument load is true on load and false on eject.
+     * Beware: doesn't run when a host device's physical media
+     * changes.  Sure would be useful if it did.
+     * Device models with removable media must implement this callback.
+     */
+    void (*change_media_cb)(void *opaque, bool load, Error **errp);
+    /*
+     * Runs when an eject request is issued from the monitor, the tray
+     * is closed, and the medium is locked.
+     * Device models that do not implement is_medium_locked will not need
+     * this callback.  Device models that can lock the medium or tray might
+     * want to implement the callback and unlock the tray when "force" is
+     * true, even if they do not support eject requests.
+     */
+    void (*eject_request_cb)(void *opaque, bool force);
+    /*
+     * Is the virtual tray open?
+     * Device models implement this only when the device has a tray.
+     */
+    bool (*is_tray_open)(void *opaque);
+    /*
+     * Is the virtual medium locked into the device?
+     * Device models implement this only when device has such a lock.
+     */
+    bool (*is_medium_locked)(void *opaque);
+    /*
+     * Runs when the size changed (e.g. monitor command block_resize)
+     */
+    void (*resize_cb)(void *opaque);
+    /*
+     * Runs when the backend receives a drain request.
+     */
+    void (*drained_begin)(void *opaque);
+    /*
+     * Runs when the backend's last drain request ends.
+     */
+    void (*drained_end)(void *opaque);
+    /*
+     * Is the device still busy?
+     */
+    bool (*drained_poll)(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 {
+    ThrottleGroupMember throttle_group_member;
+} BlockBackendPublic;
+
+#endif /* BLOCK_BACKEND_COMMON_H */
diff --git a/include/sysemu/block-backend-graph.h b/include/sysemu/block-backend-graph.h
new file mode 100644
index 0000000000..3310987b16
--- /dev/null
+++ b/include/sysemu/block-backend-graph.h
@@ -0,0 +1,132 @@ 
+/*
+ * QEMU Block backends
+ *
+ * Copyright (C) 2014-2016 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@redhat.com>,
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#ifndef BLOCK_BACKEND_GRAPH_H
+#define BLOCK_BACKEND_GRAPH_H
+
+#include "block-backend-common.h"
+
+/*
+ * Graph API. These functions run under the BQL lock.
+ *
+ * If a function modifies the graph, it uses drain and/or
+ * aio_context_acquire/release to be sure it has unique access.
+ *
+ * All functions in this header must use this assertion:
+ * g_assert(qemu_in_main_thread());
+ * to be sure they belong here.
+ */
+
+BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm);
+BlockBackend *blk_new_with_bs(BlockDriverState *bs, uint64_t perm,
+                              uint64_t shared_perm, Error **errp);
+BlockBackend *blk_new_open(const char *filename, const char *reference,
+                           QDict *options, int flags, Error **errp);
+int blk_get_refcnt(BlockBackend *blk);
+void blk_ref(BlockBackend *blk);
+void blk_unref(BlockBackend *blk);
+void blk_remove_all_bs(void);
+const char *blk_name(const BlockBackend *blk);
+BlockBackend *blk_by_name(const char *name);
+BlockBackend *blk_next(BlockBackend *blk);
+BlockBackend *blk_all_next(BlockBackend *blk);
+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);
+
+void blk_remove_bs(BlockBackend *blk);
+int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp);
+bool bdrv_has_blk(BlockDriverState *bs);
+bool bdrv_is_root_node(BlockDriverState *bs);
+int blk_set_perm(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
+                 Error **errp);
+void blk_get_perm(BlockBackend *blk, uint64_t *perm, uint64_t *shared_perm);
+
+void blk_iostatus_enable(BlockBackend *blk);
+bool blk_iostatus_is_enabled(const BlockBackend *blk);
+BlockDeviceIoStatus blk_iostatus(const BlockBackend *blk);
+void blk_iostatus_disable(BlockBackend *blk);
+void blk_iostatus_reset(BlockBackend *blk);
+void blk_iostatus_set_err(BlockBackend *blk, int error);
+int blk_attach_dev(BlockBackend *blk, DeviceState *dev);
+void blk_detach_dev(BlockBackend *blk, DeviceState *dev);
+DeviceState *blk_get_attached_dev(BlockBackend *blk);
+char *blk_get_attached_dev_id(BlockBackend *blk);
+BlockBackend *blk_by_dev(void *dev);
+BlockBackend *blk_by_qdev_id(const char *id, Error **errp);
+void blk_set_dev_ops(BlockBackend *blk, const BlockDevOps *ops, void *opaque);
+
+int blk_make_zero(BlockBackend *blk, BdrvRequestFlags flags);
+int64_t blk_nb_sectors(BlockBackend *blk);
+int blk_commit_all(void);
+void blk_drain(BlockBackend *blk);
+void blk_drain_all(void);
+void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
+                      BlockdevOnError on_write_error);
+BlockdevOnError blk_get_on_error(BlockBackend *blk, bool is_read);
+BlockErrorAction blk_get_error_action(BlockBackend *blk, bool is_read,
+                                      int error);
+void blk_error_action(BlockBackend *blk, BlockErrorAction action,
+                      bool is_read, int error);
+bool blk_supports_write_perm(BlockBackend *blk);
+bool blk_is_sg(BlockBackend *blk);
+bool blk_enable_write_cache(BlockBackend *blk);
+void blk_set_enable_write_cache(BlockBackend *blk, bool wce);
+void blk_lock_medium(BlockBackend *blk, bool locked);
+void blk_eject(BlockBackend *blk, bool eject_flag);
+int blk_get_flags(BlockBackend *blk);
+int blk_get_max_iov(BlockBackend *blk);
+void blk_set_guest_block_size(BlockBackend *blk, int align);
+bool blk_op_is_blocked(BlockBackend *blk, BlockOpType op, Error **errp);
+void blk_op_unblock(BlockBackend *blk, BlockOpType op, Error *reason);
+void blk_op_block_all(BlockBackend *blk, Error *reason);
+void blk_op_unblock_all(BlockBackend *blk, Error *reason);
+int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
+                        Error **errp);
+void blk_add_aio_context_notifier(BlockBackend *blk,
+        void (*attached_aio_context)(AioContext *new_context, void *opaque),
+        void (*detach_aio_context)(void *opaque), void *opaque);
+void blk_remove_aio_context_notifier(BlockBackend *blk,
+                                     void (*attached_aio_context)(AioContext *,
+                                                                  void *),
+                                     void (*detach_aio_context)(void *),
+                                     void *opaque);
+void blk_add_remove_bs_notifier(BlockBackend *blk, Notifier *notify);
+void blk_add_insert_bs_notifier(BlockBackend *blk, Notifier *notify);
+BlockBackendRootState *blk_get_root_state(BlockBackend *blk);
+void blk_update_root_state(BlockBackend *blk);
+bool blk_get_detect_zeroes_from_root_state(BlockBackend *blk);
+int blk_get_open_flags_from_root_state(BlockBackend *blk);
+
+int blk_save_vmstate(BlockBackend *blk, const uint8_t *buf,
+                     int64_t pos, int size);
+int blk_load_vmstate(BlockBackend *blk, uint8_t *buf, int64_t pos, int size);
+int blk_probe_blocksizes(BlockBackend *blk, BlockSizes *bsz);
+int blk_probe_geometry(BlockBackend *blk, HDGeometry *geo);
+BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
+                                  BlockCompletionFunc *cb,
+                                  void *opaque, int ret);
+
+void blk_set_io_limits(BlockBackend *blk, ThrottleConfig *cfg);
+void blk_io_limits_disable(BlockBackend *blk);
+void blk_io_limits_enable(BlockBackend *blk, const char *group);
+void blk_io_limits_update_group(BlockBackend *blk, const char *group);
+void blk_set_force_allow_inactivate(BlockBackend *blk);
+
+void blk_register_buf(BlockBackend *blk, void *host, size_t size);
+void blk_unregister_buf(BlockBackend *blk, void *host);
+
+const BdrvChild *blk_root(BlockBackend *blk);
+
+#endif /* BLOCK_BACKEND_GRAPH_H */
diff --git a/include/sysemu/block-backend-io.h b/include/sysemu/block-backend-io.h
new file mode 100644
index 0000000000..66a7bed9f0
--- /dev/null
+++ b/include/sysemu/block-backend-io.h
@@ -0,0 +1,123 @@ 
+/*
+ * QEMU Block backends
+ *
+ * Copyright (C) 2014-2016 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@redhat.com>,
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#ifndef BLOCK_BACKEND_IO_H
+#define BLOCK_BACKEND_IO_H
+
+#include "block-backend-common.h"
+
+/*
+ * I/O API functions. These functions are thread-safe, and therefore
+ * can run in any AioContext.
+ */
+
+BlockDriverState *blk_bs(BlockBackend *blk);
+
+void blk_set_allow_write_beyond_eof(BlockBackend *blk, bool allow);
+void blk_set_allow_aio_context_change(BlockBackend *blk, bool allow);
+void blk_set_disable_request_queuing(BlockBackend *blk, bool disable);
+
+int blk_pread(BlockBackend *blk, int64_t offset, void *buf, int bytes);
+int blk_pwrite(BlockBackend *blk, int64_t offset, const void *buf, int bytes,
+               BdrvRequestFlags flags);
+int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
+                               unsigned int bytes, QEMUIOVector *qiov,
+                               BdrvRequestFlags flags);
+int coroutine_fn blk_co_pwritev_part(BlockBackend *blk, int64_t offset,
+                                     unsigned int bytes,
+                                     QEMUIOVector *qiov, size_t qiov_offset,
+                                     BdrvRequestFlags flags);
+int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
+                               unsigned int bytes, QEMUIOVector *qiov,
+                               BdrvRequestFlags flags);
+
+static inline int coroutine_fn blk_co_pread(BlockBackend *blk, int64_t offset,
+                                            unsigned int bytes, void *buf,
+                                            BdrvRequestFlags flags)
+{
+    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf, bytes);
+
+    return blk_co_preadv(blk, offset, bytes, &qiov, flags);
+}
+
+static inline int coroutine_fn blk_co_pwrite(BlockBackend *blk, int64_t offset,
+                                             unsigned int bytes, void *buf,
+                                             BdrvRequestFlags flags)
+{
+    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf, bytes);
+
+    return blk_co_pwritev(blk, offset, bytes, &qiov, flags);
+}
+
+BlockAIOCB *blk_aio_pwrite_zeroes(BlockBackend *blk, int64_t offset,
+                                  int bytes, BdrvRequestFlags flags,
+                                  BlockCompletionFunc *cb, void *opaque);
+
+BlockAIOCB *blk_aio_preadv(BlockBackend *blk, int64_t offset,
+                           QEMUIOVector *qiov, BdrvRequestFlags flags,
+                           BlockCompletionFunc *cb, void *opaque);
+BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset,
+                            QEMUIOVector *qiov, BdrvRequestFlags flags,
+                            BlockCompletionFunc *cb, void *opaque);
+BlockAIOCB *blk_aio_flush(BlockBackend *blk,
+                          BlockCompletionFunc *cb, void *opaque);
+BlockAIOCB *blk_aio_pdiscard(BlockBackend *blk, int64_t offset, int bytes,
+                             BlockCompletionFunc *cb, void *opaque);
+void blk_aio_cancel(BlockAIOCB *acb);
+void blk_aio_cancel_async(BlockAIOCB *acb);
+int blk_ioctl(BlockBackend *blk, unsigned long int req, void *buf);
+BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, void *buf,
+                          BlockCompletionFunc *cb, void *opaque);
+int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int bytes);
+int blk_co_flush(BlockBackend *blk);
+int blk_flush(BlockBackend *blk);
+void blk_inc_in_flight(BlockBackend *blk);
+void blk_dec_in_flight(BlockBackend *blk);
+bool blk_is_inserted(BlockBackend *blk);
+bool blk_is_available(BlockBackend *blk);
+int64_t blk_getlength(BlockBackend *blk);
+void blk_get_geometry(BlockBackend *blk, uint64_t *nb_sectors_ptr);
+void *blk_try_blockalign(BlockBackend *blk, size_t size);
+void *blk_blockalign(BlockBackend *blk, size_t size);
+bool blk_is_writable(BlockBackend *blk);
+
+void blk_invalidate_cache(BlockBackend *blk, Error **errp);
+
+void blk_io_plug(BlockBackend *blk);
+void blk_io_unplug(BlockBackend *blk);
+AioContext *blk_get_aio_context(BlockBackend *blk);
+BlockAcctStats *blk_get_stats(BlockBackend *blk);
+void *blk_aio_get(const AIOCBInfo *aiocb_info, BlockBackend *blk,
+                  BlockCompletionFunc *cb, void *opaque);
+int blk_pwrite_compressed(BlockBackend *blk, int64_t offset, const void *buf,
+                          int bytes);
+int blk_pdiscard(BlockBackend *blk, int64_t offset, int bytes);
+int blk_pwrite_zeroes(BlockBackend *blk, int64_t offset,
+                      int bytes, BdrvRequestFlags flags);
+int coroutine_fn blk_co_pwrite_zeroes(BlockBackend *blk, int64_t offset,
+                                      int bytes, BdrvRequestFlags flags);
+int blk_truncate(BlockBackend *blk, int64_t offset, bool exact,
+                 PreallocMode prealloc, BdrvRequestFlags flags, Error **errp);
+
+uint32_t blk_get_request_alignment(BlockBackend *blk);
+uint32_t blk_get_max_transfer(BlockBackend *blk);
+uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
+
+int coroutine_fn blk_co_copy_range(BlockBackend *blk_in, int64_t off_in,
+                                   BlockBackend *blk_out, int64_t off_out,
+                                   int bytes, BdrvRequestFlags read_flags,
+                                   BdrvRequestFlags write_flags);
+
+
+int blk_make_empty(BlockBackend *blk, Error **errp);
+
+#endif /* BLOCK_BACKEND_IO_H */
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 9ac5f7bbd3..8c64a46008 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -13,265 +13,9 @@ 
 #ifndef BLOCK_BACKEND_H
 #define BLOCK_BACKEND_H
 
-#include "qemu/iov.h"
-#include "block/throttle-groups.h"
+#include "block-backend-graph.h"
+#include "block-backend-io.h"
 
-/*
- * TODO Have to include block/block.h for a bunch of block layer
- * types.  Unfortunately, this pulls in the whole BlockDriverState
- * API, which we don't want used by many BlockBackend users.  Some of
- * the types belong here, and the rest should be split into a common
- * header and one for the BlockDriverState API.
- */
-#include "block/block.h"
-
-/* Callbacks for block device models */
-typedef struct BlockDevOps {
-    /*
-     * Runs when virtual media changed (monitor commands eject, change)
-     * Argument load is true on load and false on eject.
-     * Beware: doesn't run when a host device's physical media
-     * changes.  Sure would be useful if it did.
-     * Device models with removable media must implement this callback.
-     */
-    void (*change_media_cb)(void *opaque, bool load, Error **errp);
-    /*
-     * Runs when an eject request is issued from the monitor, the tray
-     * is closed, and the medium is locked.
-     * Device models that do not implement is_medium_locked will not need
-     * this callback.  Device models that can lock the medium or tray might
-     * want to implement the callback and unlock the tray when "force" is
-     * true, even if they do not support eject requests.
-     */
-    void (*eject_request_cb)(void *opaque, bool force);
-    /*
-     * Is the virtual tray open?
-     * Device models implement this only when the device has a tray.
-     */
-    bool (*is_tray_open)(void *opaque);
-    /*
-     * Is the virtual medium locked into the device?
-     * Device models implement this only when device has such a lock.
-     */
-    bool (*is_medium_locked)(void *opaque);
-    /*
-     * Runs when the size changed (e.g. monitor command block_resize)
-     */
-    void (*resize_cb)(void *opaque);
-    /*
-     * Runs when the backend receives a drain request.
-     */
-    void (*drained_begin)(void *opaque);
-    /*
-     * Runs when the backend's last drain request ends.
-     */
-    void (*drained_end)(void *opaque);
-    /*
-     * Is the device still busy?
-     */
-    bool (*drained_poll)(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 {
-    ThrottleGroupMember throttle_group_member;
-} BlockBackendPublic;
-
-BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm);
-BlockBackend *blk_new_with_bs(BlockDriverState *bs, uint64_t perm,
-                              uint64_t shared_perm, Error **errp);
-BlockBackend *blk_new_open(const char *filename, const char *reference,
-                           QDict *options, int flags, Error **errp);
-int blk_get_refcnt(BlockBackend *blk);
-void blk_ref(BlockBackend *blk);
-void blk_unref(BlockBackend *blk);
-void blk_remove_all_bs(void);
-const char *blk_name(const BlockBackend *blk);
-BlockBackend *blk_by_name(const char *name);
-BlockBackend *blk_next(BlockBackend *blk);
-BlockBackend *blk_all_next(BlockBackend *blk);
-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);
-int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp);
-bool bdrv_has_blk(BlockDriverState *bs);
-bool bdrv_is_root_node(BlockDriverState *bs);
-int blk_set_perm(BlockBackend *blk, uint64_t perm, uint64_t shared_perm,
-                 Error **errp);
-void blk_get_perm(BlockBackend *blk, uint64_t *perm, uint64_t *shared_perm);
-
-void blk_set_allow_write_beyond_eof(BlockBackend *blk, bool allow);
-void blk_set_allow_aio_context_change(BlockBackend *blk, bool allow);
-void blk_set_disable_request_queuing(BlockBackend *blk, bool disable);
-void blk_iostatus_enable(BlockBackend *blk);
-bool blk_iostatus_is_enabled(const BlockBackend *blk);
-BlockDeviceIoStatus blk_iostatus(const BlockBackend *blk);
-void blk_iostatus_disable(BlockBackend *blk);
-void blk_iostatus_reset(BlockBackend *blk);
-void blk_iostatus_set_err(BlockBackend *blk, int error);
-int blk_attach_dev(BlockBackend *blk, DeviceState *dev);
-void blk_detach_dev(BlockBackend *blk, DeviceState *dev);
-DeviceState *blk_get_attached_dev(BlockBackend *blk);
-char *blk_get_attached_dev_id(BlockBackend *blk);
-BlockBackend *blk_by_dev(void *dev);
-BlockBackend *blk_by_qdev_id(const char *id, Error **errp);
-void blk_set_dev_ops(BlockBackend *blk, const BlockDevOps *ops, void *opaque);
-int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
-                               unsigned int bytes, QEMUIOVector *qiov,
-                               BdrvRequestFlags flags);
-int coroutine_fn blk_co_pwritev_part(BlockBackend *blk, int64_t offset,
-                                     unsigned int bytes,
-                                     QEMUIOVector *qiov, size_t qiov_offset,
-                                     BdrvRequestFlags flags);
-int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
-                               unsigned int bytes, QEMUIOVector *qiov,
-                               BdrvRequestFlags flags);
-
-static inline int coroutine_fn blk_co_pread(BlockBackend *blk, int64_t offset,
-                                            unsigned int bytes, void *buf,
-                                            BdrvRequestFlags flags)
-{
-    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf, bytes);
-
-    return blk_co_preadv(blk, offset, bytes, &qiov, flags);
-}
-
-static inline int coroutine_fn blk_co_pwrite(BlockBackend *blk, int64_t offset,
-                                             unsigned int bytes, void *buf,
-                                             BdrvRequestFlags flags)
-{
-    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf, bytes);
-
-    return blk_co_pwritev(blk, offset, bytes, &qiov, flags);
-}
-
-int blk_pwrite_zeroes(BlockBackend *blk, int64_t offset,
-                      int bytes, BdrvRequestFlags flags);
-BlockAIOCB *blk_aio_pwrite_zeroes(BlockBackend *blk, int64_t offset,
-                                  int bytes, BdrvRequestFlags flags,
-                                  BlockCompletionFunc *cb, void *opaque);
-int blk_make_zero(BlockBackend *blk, BdrvRequestFlags flags);
-int blk_pread(BlockBackend *blk, int64_t offset, void *buf, int bytes);
-int blk_pwrite(BlockBackend *blk, int64_t offset, const void *buf, int bytes,
-               BdrvRequestFlags flags);
-int64_t blk_getlength(BlockBackend *blk);
-void blk_get_geometry(BlockBackend *blk, uint64_t *nb_sectors_ptr);
-int64_t blk_nb_sectors(BlockBackend *blk);
-BlockAIOCB *blk_aio_preadv(BlockBackend *blk, int64_t offset,
-                           QEMUIOVector *qiov, BdrvRequestFlags flags,
-                           BlockCompletionFunc *cb, void *opaque);
-BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset,
-                            QEMUIOVector *qiov, BdrvRequestFlags flags,
-                            BlockCompletionFunc *cb, void *opaque);
-BlockAIOCB *blk_aio_flush(BlockBackend *blk,
-                          BlockCompletionFunc *cb, void *opaque);
-BlockAIOCB *blk_aio_pdiscard(BlockBackend *blk, int64_t offset, int bytes,
-                             BlockCompletionFunc *cb, void *opaque);
-void blk_aio_cancel(BlockAIOCB *acb);
-void blk_aio_cancel_async(BlockAIOCB *acb);
-int blk_ioctl(BlockBackend *blk, unsigned long int req, void *buf);
-BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, void *buf,
-                          BlockCompletionFunc *cb, void *opaque);
-int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int bytes);
-int blk_co_flush(BlockBackend *blk);
-int blk_flush(BlockBackend *blk);
-int blk_commit_all(void);
-void blk_inc_in_flight(BlockBackend *blk);
-void blk_dec_in_flight(BlockBackend *blk);
-void blk_drain(BlockBackend *blk);
-void blk_drain_all(void);
-void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
-                      BlockdevOnError on_write_error);
-BlockdevOnError blk_get_on_error(BlockBackend *blk, bool is_read);
-BlockErrorAction blk_get_error_action(BlockBackend *blk, bool is_read,
-                                      int error);
-void blk_error_action(BlockBackend *blk, BlockErrorAction action,
-                      bool is_read, int error);
-bool blk_supports_write_perm(BlockBackend *blk);
-bool blk_is_writable(BlockBackend *blk);
-bool blk_is_sg(BlockBackend *blk);
-bool blk_enable_write_cache(BlockBackend *blk);
-void blk_set_enable_write_cache(BlockBackend *blk, bool wce);
-void blk_invalidate_cache(BlockBackend *blk, Error **errp);
-bool blk_is_inserted(BlockBackend *blk);
-bool blk_is_available(BlockBackend *blk);
-void blk_lock_medium(BlockBackend *blk, bool locked);
-void blk_eject(BlockBackend *blk, bool eject_flag);
-int blk_get_flags(BlockBackend *blk);
-uint32_t blk_get_request_alignment(BlockBackend *blk);
-uint32_t blk_get_max_transfer(BlockBackend *blk);
-uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
-int blk_get_max_iov(BlockBackend *blk);
-void blk_set_guest_block_size(BlockBackend *blk, int align);
-void *blk_try_blockalign(BlockBackend *blk, size_t size);
-void *blk_blockalign(BlockBackend *blk, size_t size);
-bool blk_op_is_blocked(BlockBackend *blk, BlockOpType op, Error **errp);
-void blk_op_unblock(BlockBackend *blk, BlockOpType op, Error *reason);
-void blk_op_block_all(BlockBackend *blk, Error *reason);
-void blk_op_unblock_all(BlockBackend *blk, Error *reason);
-AioContext *blk_get_aio_context(BlockBackend *blk);
-int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
-                        Error **errp);
-void blk_add_aio_context_notifier(BlockBackend *blk,
-        void (*attached_aio_context)(AioContext *new_context, void *opaque),
-        void (*detach_aio_context)(void *opaque), void *opaque);
-void blk_remove_aio_context_notifier(BlockBackend *blk,
-                                     void (*attached_aio_context)(AioContext *,
-                                                                  void *),
-                                     void (*detach_aio_context)(void *),
-                                     void *opaque);
-void blk_add_remove_bs_notifier(BlockBackend *blk, Notifier *notify);
-void blk_add_insert_bs_notifier(BlockBackend *blk, Notifier *notify);
-void blk_io_plug(BlockBackend *blk);
-void blk_io_unplug(BlockBackend *blk);
-BlockAcctStats *blk_get_stats(BlockBackend *blk);
-BlockBackendRootState *blk_get_root_state(BlockBackend *blk);
-void blk_update_root_state(BlockBackend *blk);
-bool blk_get_detect_zeroes_from_root_state(BlockBackend *blk);
-int blk_get_open_flags_from_root_state(BlockBackend *blk);
-
-void *blk_aio_get(const AIOCBInfo *aiocb_info, BlockBackend *blk,
-                  BlockCompletionFunc *cb, void *opaque);
-int coroutine_fn blk_co_pwrite_zeroes(BlockBackend *blk, int64_t offset,
-                                      int bytes, BdrvRequestFlags flags);
-int blk_pwrite_compressed(BlockBackend *blk, int64_t offset, const void *buf,
-                          int bytes);
-int blk_truncate(BlockBackend *blk, int64_t offset, bool exact,
-                 PreallocMode prealloc, BdrvRequestFlags flags, Error **errp);
-int blk_pdiscard(BlockBackend *blk, int64_t offset, int bytes);
-int blk_save_vmstate(BlockBackend *blk, const uint8_t *buf,
-                     int64_t pos, int size);
-int blk_load_vmstate(BlockBackend *blk, uint8_t *buf, int64_t pos, int size);
-int blk_probe_blocksizes(BlockBackend *blk, BlockSizes *bsz);
-int blk_probe_geometry(BlockBackend *blk, HDGeometry *geo);
-BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
-                                  BlockCompletionFunc *cb,
-                                  void *opaque, int ret);
-
-void blk_set_io_limits(BlockBackend *blk, ThrottleConfig *cfg);
-void blk_io_limits_disable(BlockBackend *blk);
-void blk_io_limits_enable(BlockBackend *blk, const char *group);
-void blk_io_limits_update_group(BlockBackend *blk, const char *group);
-void blk_set_force_allow_inactivate(BlockBackend *blk);
-
-void blk_register_buf(BlockBackend *blk, void *host, size_t size);
-void blk_unregister_buf(BlockBackend *blk, void *host);
-
-int coroutine_fn blk_co_copy_range(BlockBackend *blk_in, int64_t off_in,
-                                   BlockBackend *blk_out, int64_t off_out,
-                                   int bytes, BdrvRequestFlags read_flags,
-                                   BdrvRequestFlags write_flags);
-
-const BdrvChild *blk_root(BlockBackend *blk);
-
-int blk_make_empty(BlockBackend *blk, Error **errp);
+/* DO NOT ADD ANYTHING IN HERE. USE ONE OF THE HEADERS INCLUDED ABOVE */
 
 #endif