This will be used by BDRV_POLL_WHILE (and thus by bdrv_drain) to choose how to wait for I/O completion. Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <1477565348-5458-12-git-send-email-pbonzini@redhat.com> Signed-off-by: Fam Zheng <famz@redhat.com>
482 lines
15 KiB
C
482 lines
15 KiB
C
/*
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* QEMU aio implementation
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*
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* Copyright IBM, Corp. 2008
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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*/
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#ifndef QEMU_AIO_H
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#define QEMU_AIO_H
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#include "qemu-common.h"
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#include "qemu/queue.h"
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#include "qemu/event_notifier.h"
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#include "qemu/thread.h"
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#include "qemu/rfifolock.h"
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#include "qemu/timer.h"
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typedef struct BlockAIOCB BlockAIOCB;
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typedef void BlockCompletionFunc(void *opaque, int ret);
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typedef struct AIOCBInfo {
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void (*cancel_async)(BlockAIOCB *acb);
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AioContext *(*get_aio_context)(BlockAIOCB *acb);
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size_t aiocb_size;
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} AIOCBInfo;
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struct BlockAIOCB {
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const AIOCBInfo *aiocb_info;
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BlockDriverState *bs;
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BlockCompletionFunc *cb;
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void *opaque;
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int refcnt;
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};
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void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
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BlockCompletionFunc *cb, void *opaque);
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void qemu_aio_unref(void *p);
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void qemu_aio_ref(void *p);
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typedef struct AioHandler AioHandler;
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typedef void QEMUBHFunc(void *opaque);
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typedef void IOHandler(void *opaque);
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struct ThreadPool;
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struct LinuxAioState;
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struct AioContext {
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GSource source;
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/* Protects all fields from multi-threaded access */
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RFifoLock lock;
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/* The list of registered AIO handlers */
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QLIST_HEAD(, AioHandler) aio_handlers;
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/* This is a simple lock used to protect the aio_handlers list.
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* Specifically, it's used to ensure that no callbacks are removed while
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* we're walking and dispatching callbacks.
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*/
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int walking_handlers;
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/* Used to avoid unnecessary event_notifier_set calls in aio_notify;
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* accessed with atomic primitives. If this field is 0, everything
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* (file descriptors, bottom halves, timers) will be re-evaluated
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* before the next blocking poll(), thus the event_notifier_set call
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* can be skipped. If it is non-zero, you may need to wake up a
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* concurrent aio_poll or the glib main event loop, making
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* event_notifier_set necessary.
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*
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* Bit 0 is reserved for GSource usage of the AioContext, and is 1
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* between a call to aio_ctx_prepare and the next call to aio_ctx_check.
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* Bits 1-31 simply count the number of active calls to aio_poll
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* that are in the prepare or poll phase.
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*
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* The GSource and aio_poll must use a different mechanism because
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* there is no certainty that a call to GSource's prepare callback
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* (via g_main_context_prepare) is indeed followed by check and
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* dispatch. It's not clear whether this would be a bug, but let's
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* play safe and allow it---it will just cause extra calls to
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* event_notifier_set until the next call to dispatch.
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*
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* Instead, the aio_poll calls include both the prepare and the
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* dispatch phase, hence a simple counter is enough for them.
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*/
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uint32_t notify_me;
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/* lock to protect between bh's adders and deleter */
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QemuMutex bh_lock;
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/* Anchor of the list of Bottom Halves belonging to the context */
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struct QEMUBH *first_bh;
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/* A simple lock used to protect the first_bh list, and ensure that
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* no callbacks are removed while we're walking and dispatching callbacks.
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*/
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int walking_bh;
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/* Used by aio_notify.
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*
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* "notified" is used to avoid expensive event_notifier_test_and_clear
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* calls. When it is clear, the EventNotifier is clear, or one thread
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* is going to clear "notified" before processing more events. False
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* positives are possible, i.e. "notified" could be set even though the
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* EventNotifier is clear.
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*
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* Note that event_notifier_set *cannot* be optimized the same way. For
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* more information on the problem that would result, see "#ifdef BUG2"
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* in the docs/aio_notify_accept.promela formal model.
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*/
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bool notified;
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EventNotifier notifier;
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/* Scheduling this BH forces the event loop it iterate */
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QEMUBH *notify_dummy_bh;
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/* Thread pool for performing work and receiving completion callbacks */
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struct ThreadPool *thread_pool;
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#ifdef CONFIG_LINUX_AIO
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/* State for native Linux AIO. Uses aio_context_acquire/release for
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* locking.
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*/
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struct LinuxAioState *linux_aio;
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#endif
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/* TimerLists for calling timers - one per clock type */
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QEMUTimerListGroup tlg;
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int external_disable_cnt;
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/* epoll(7) state used when built with CONFIG_EPOLL */
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int epollfd;
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bool epoll_enabled;
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bool epoll_available;
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};
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/**
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* aio_context_new: Allocate a new AioContext.
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*
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* AioContext provide a mini event-loop that can be waited on synchronously.
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* They also provide bottom halves, a service to execute a piece of code
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* as soon as possible.
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*/
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AioContext *aio_context_new(Error **errp);
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/**
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* aio_context_ref:
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* @ctx: The AioContext to operate on.
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*
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* Add a reference to an AioContext.
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*/
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void aio_context_ref(AioContext *ctx);
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/**
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* aio_context_unref:
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* @ctx: The AioContext to operate on.
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*
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* Drop a reference to an AioContext.
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*/
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void aio_context_unref(AioContext *ctx);
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/* Take ownership of the AioContext. If the AioContext will be shared between
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* threads, and a thread does not want to be interrupted, it will have to
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* take ownership around calls to aio_poll(). Otherwise, aio_poll()
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* automatically takes care of calling aio_context_acquire and
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* aio_context_release.
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*
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* Access to timers and BHs from a thread that has not acquired AioContext
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* is possible. Access to callbacks for now must be done while the AioContext
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* is owned by the thread (FIXME).
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*/
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void aio_context_acquire(AioContext *ctx);
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/* Relinquish ownership of the AioContext. */
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void aio_context_release(AioContext *ctx);
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/**
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* aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run
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* only once and as soon as possible.
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*/
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void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
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/**
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* aio_bh_new: Allocate a new bottom half structure.
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*
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* Bottom halves are lightweight callbacks whose invocation is guaranteed
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* to be wait-free, thread-safe and signal-safe. The #QEMUBH structure
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* is opaque and must be allocated prior to its use.
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*/
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QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
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/**
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* aio_notify: Force processing of pending events.
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*
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* Similar to signaling a condition variable, aio_notify forces
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* aio_wait to exit, so that the next call will re-examine pending events.
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* The caller of aio_notify will usually call aio_wait again very soon,
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* or go through another iteration of the GLib main loop. Hence, aio_notify
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* also has the side effect of recalculating the sets of file descriptors
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* that the main loop waits for.
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*
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* Calling aio_notify is rarely necessary, because for example scheduling
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* a bottom half calls it already.
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*/
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void aio_notify(AioContext *ctx);
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/**
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* aio_notify_accept: Acknowledge receiving an aio_notify.
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*
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* aio_notify() uses an EventNotifier in order to wake up a sleeping
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* aio_poll() or g_main_context_iteration(). Calls to aio_notify() are
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* usually rare, but the AioContext has to clear the EventNotifier on
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* every aio_poll() or g_main_context_iteration() in order to avoid
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* busy waiting. This event_notifier_test_and_clear() cannot be done
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* using the usual aio_context_set_event_notifier(), because it must
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* be done before processing all events (file descriptors, bottom halves,
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* timers).
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*
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* aio_notify_accept() is an optimized event_notifier_test_and_clear()
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* that is specific to an AioContext's notifier; it is used internally
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* to clear the EventNotifier only if aio_notify() had been called.
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*/
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void aio_notify_accept(AioContext *ctx);
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/**
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* aio_bh_call: Executes callback function of the specified BH.
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*/
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void aio_bh_call(QEMUBH *bh);
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/**
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* aio_bh_poll: Poll bottom halves for an AioContext.
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*
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* These are internal functions used by the QEMU main loop.
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* And notice that multiple occurrences of aio_bh_poll cannot
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* be called concurrently
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*/
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int aio_bh_poll(AioContext *ctx);
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/**
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* qemu_bh_schedule: Schedule a bottom half.
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*
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* Scheduling a bottom half interrupts the main loop and causes the
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* execution of the callback that was passed to qemu_bh_new.
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*
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* Bottom halves that are scheduled from a bottom half handler are instantly
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* invoked. This can create an infinite loop if a bottom half handler
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* schedules itself.
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*
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* @bh: The bottom half to be scheduled.
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*/
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void qemu_bh_schedule(QEMUBH *bh);
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/**
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* qemu_bh_cancel: Cancel execution of a bottom half.
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*
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* Canceling execution of a bottom half undoes the effect of calls to
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* qemu_bh_schedule without freeing its resources yet. While cancellation
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* itself is also wait-free and thread-safe, it can of course race with the
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* loop that executes bottom halves unless you are holding the iothread
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* mutex. This makes it mostly useless if you are not holding the mutex.
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*
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* @bh: The bottom half to be canceled.
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*/
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void qemu_bh_cancel(QEMUBH *bh);
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/**
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*qemu_bh_delete: Cancel execution of a bottom half and free its resources.
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*
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* Deleting a bottom half frees the memory that was allocated for it by
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* qemu_bh_new. It also implies canceling the bottom half if it was
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* scheduled.
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* This func is async. The bottom half will do the delete action at the finial
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* end.
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*
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* @bh: The bottom half to be deleted.
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*/
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void qemu_bh_delete(QEMUBH *bh);
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/* Return whether there are any pending callbacks from the GSource
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* attached to the AioContext, before g_poll is invoked.
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*
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* This is used internally in the implementation of the GSource.
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*/
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bool aio_prepare(AioContext *ctx);
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/* Return whether there are any pending callbacks from the GSource
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* attached to the AioContext, after g_poll is invoked.
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*
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* This is used internally in the implementation of the GSource.
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*/
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bool aio_pending(AioContext *ctx);
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/* Dispatch any pending callbacks from the GSource attached to the AioContext.
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*
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* This is used internally in the implementation of the GSource.
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*/
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bool aio_dispatch(AioContext *ctx);
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/* Progress in completing AIO work to occur. This can issue new pending
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* aio as a result of executing I/O completion or bh callbacks.
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*
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* Return whether any progress was made by executing AIO or bottom half
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* handlers. If @blocking == true, this should always be true except
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* if someone called aio_notify.
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*
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* If there are no pending bottom halves, but there are pending AIO
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* operations, it may not be possible to make any progress without
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* blocking. If @blocking is true, this function will wait until one
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* or more AIO events have completed, to ensure something has moved
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* before returning.
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*/
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bool aio_poll(AioContext *ctx, bool blocking);
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/* Register a file descriptor and associated callbacks. Behaves very similarly
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* to qemu_set_fd_handler. Unlike qemu_set_fd_handler, these callbacks will
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* be invoked when using aio_poll().
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*
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* Code that invokes AIO completion functions should rely on this function
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* instead of qemu_set_fd_handler[2].
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*/
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void aio_set_fd_handler(AioContext *ctx,
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int fd,
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bool is_external,
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IOHandler *io_read,
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IOHandler *io_write,
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void *opaque);
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/* Register an event notifier and associated callbacks. Behaves very similarly
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* to event_notifier_set_handler. Unlike event_notifier_set_handler, these callbacks
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* will be invoked when using aio_poll().
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*
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* Code that invokes AIO completion functions should rely on this function
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* instead of event_notifier_set_handler.
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*/
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void aio_set_event_notifier(AioContext *ctx,
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EventNotifier *notifier,
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bool is_external,
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EventNotifierHandler *io_read);
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/* Return a GSource that lets the main loop poll the file descriptors attached
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* to this AioContext.
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*/
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GSource *aio_get_g_source(AioContext *ctx);
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/* Return the ThreadPool bound to this AioContext */
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struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
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/* Return the LinuxAioState bound to this AioContext */
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struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
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/**
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* aio_timer_new:
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* @ctx: the aio context
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* @type: the clock type
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* @scale: the scale
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* @cb: the callback to call on timer expiry
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* @opaque: the opaque pointer to pass to the callback
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*
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* Allocate a new timer attached to the context @ctx.
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* The function is responsible for memory allocation.
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*
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* The preferred interface is aio_timer_init. Use that
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* unless you really need dynamic memory allocation.
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*
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* Returns: a pointer to the new timer
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*/
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static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type,
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int scale,
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QEMUTimerCB *cb, void *opaque)
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{
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return timer_new_tl(ctx->tlg.tl[type], scale, cb, opaque);
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}
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/**
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* aio_timer_init:
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* @ctx: the aio context
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* @ts: the timer
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* @type: the clock type
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* @scale: the scale
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* @cb: the callback to call on timer expiry
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* @opaque: the opaque pointer to pass to the callback
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*
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* Initialise a new timer attached to the context @ctx.
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* The caller is responsible for memory allocation.
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*/
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static inline void aio_timer_init(AioContext *ctx,
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QEMUTimer *ts, QEMUClockType type,
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int scale,
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QEMUTimerCB *cb, void *opaque)
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{
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timer_init_tl(ts, ctx->tlg.tl[type], scale, cb, opaque);
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}
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/**
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* aio_compute_timeout:
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* @ctx: the aio context
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*
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* Compute the timeout that a blocking aio_poll should use.
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*/
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int64_t aio_compute_timeout(AioContext *ctx);
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/**
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* aio_disable_external:
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* @ctx: the aio context
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*
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* Disable the further processing of external clients.
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*/
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static inline void aio_disable_external(AioContext *ctx)
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{
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atomic_inc(&ctx->external_disable_cnt);
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}
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/**
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* aio_enable_external:
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* @ctx: the aio context
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*
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* Enable the processing of external clients.
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*/
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static inline void aio_enable_external(AioContext *ctx)
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{
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assert(ctx->external_disable_cnt > 0);
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atomic_dec(&ctx->external_disable_cnt);
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}
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/**
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* aio_external_disabled:
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* @ctx: the aio context
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*
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* Return true if the external clients are disabled.
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*/
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static inline bool aio_external_disabled(AioContext *ctx)
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{
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return atomic_read(&ctx->external_disable_cnt);
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}
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/**
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* aio_node_check:
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* @ctx: the aio context
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* @is_external: Whether or not the checked node is an external event source.
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*
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* Check if the node's is_external flag is okay to be polled by the ctx at this
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* moment. True means green light.
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*/
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static inline bool aio_node_check(AioContext *ctx, bool is_external)
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{
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return !is_external || !atomic_read(&ctx->external_disable_cnt);
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}
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/**
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* Return the AioContext whose event loop runs in the current thread.
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*
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* If called from an IOThread this will be the IOThread's AioContext. If
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* called from another thread it will be the main loop AioContext.
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*/
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AioContext *qemu_get_current_aio_context(void);
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/**
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* @ctx: the aio context
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*
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* Return whether we are running in the I/O thread that manages @ctx.
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*/
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static inline bool aio_context_in_iothread(AioContext *ctx)
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{
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return ctx == qemu_get_current_aio_context();
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}
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/**
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* aio_context_setup:
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* @ctx: the aio context
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*
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* Initialize the aio context.
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*/
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void aio_context_setup(AioContext *ctx);
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#endif
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