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