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/*
* QEMU System Emulator
*
* Copyright (c) 2003-2008 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu-common.h"
#include "qemu-aio.h"
/*
* An AsyncContext protects the callbacks of AIO requests and Bottom Halves
* against interfering with each other. A typical example is qcow2 that accepts
* asynchronous requests, but relies for manipulation of its metadata on
* synchronous bdrv_read/write that doesn't trigger any callbacks.
*
* However, these functions are often emulated using AIO which means that AIO
* callbacks must be run - but at the same time we must not run callbacks of
* other requests as they might start to modify metadata and corrupt the
* internal state of the caller of bdrv_read/write.
*
* To achieve the desired semantics we switch into a new AsyncContext.
* Callbacks must only be run if they belong to the current AsyncContext.
* Otherwise they need to be queued until their own context is active again.
* This is how you can make qemu_aio_wait() wait only for your own callbacks.
*
* The AsyncContexts form a stack. When you leave a AsyncContexts, you always
* return to the old ("parent") context.
*/
struct AsyncContext {
/* Consecutive number of the AsyncContext (position in the stack) */
int id;
/* Anchor of the list of Bottom Halves belonging to the context */
struct QEMUBH *first_bh;
/* Link to parent context */
struct AsyncContext *parent;
};
/* The currently active AsyncContext */
static struct AsyncContext *async_context = &(struct AsyncContext) { 0 };
/*
* Enter a new AsyncContext. Already scheduled Bottom Halves and AIO callbacks
* won't be called until this context is left again.
*/
void async_context_push(void)
{
struct AsyncContext *new = qemu_mallocz(sizeof(*new));
new->parent = async_context;
new->id = async_context->id + 1;
async_context = new;
}
/* Run queued AIO completions and destroy Bottom Half */
static void bh_run_aio_completions(void *opaque)
{
QEMUBH **bh = opaque;
qemu_bh_delete(*bh);
qemu_free(bh);
qemu_aio_process_queue();
}
/*
* Leave the currently active AsyncContext. All Bottom Halves belonging to the
* old context are executed before changing the context.
*/
void async_context_pop(void)
{
struct AsyncContext *old = async_context;
QEMUBH **bh;
/* Flush the bottom halves, we don't want to lose them */
while (qemu_bh_poll());
/* Switch back to the parent context */
async_context = async_context->parent;
qemu_free(old);
if (async_context == NULL) {
abort();
}
/* Schedule BH to run any queued AIO completions as soon as possible */
bh = qemu_malloc(sizeof(*bh));
*bh = qemu_bh_new(bh_run_aio_completions, bh);
qemu_bh_schedule(*bh);
}
/*
* Returns the ID of the currently active AsyncContext
*/
int get_async_context_id(void)
{
return async_context->id;
}
/***********************************************************/
/* bottom halves (can be seen as timers which expire ASAP) */
struct QEMUBH {
QEMUBHFunc *cb;
void *opaque;
int scheduled;
int idle;
int deleted;
QEMUBH *next;
};
QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
{
QEMUBH *bh;
bh = qemu_mallocz(sizeof(QEMUBH));
bh->cb = cb;
bh->opaque = opaque;
bh->next = async_context->first_bh;
async_context->first_bh = bh;
return bh;
}
int qemu_bh_poll(void)
{
QEMUBH *bh, **bhp, *next;
int ret;
ret = 0;
for (bh = async_context->first_bh; bh; bh = next) {
next = bh->next;
if (!bh->deleted && bh->scheduled) {
bh->scheduled = 0;
if (!bh->idle)
ret = 1;
bh->idle = 0;
bh->cb(bh->opaque);
}
}
/* remove deleted bhs */
bhp = &async_context->first_bh;
while (*bhp) {
bh = *bhp;
if (bh->deleted) {
*bhp = bh->next;
qemu_free(bh);
} else
bhp = &bh->next;
}
return ret;
}
void qemu_bh_schedule_idle(QEMUBH *bh)
{
if (bh->scheduled)
return;
bh->scheduled = 1;
bh->idle = 1;
}
void qemu_bh_schedule(QEMUBH *bh)
{
if (bh->scheduled)
return;
bh->scheduled = 1;
bh->idle = 0;
/* stop the currently executing CPU to execute the BH ASAP */
qemu_notify_event();
}
void qemu_bh_cancel(QEMUBH *bh)
{
bh->scheduled = 0;
}
void qemu_bh_delete(QEMUBH *bh)
{
bh->scheduled = 0;
bh->deleted = 1;
}
void qemu_bh_update_timeout(int *timeout)
{
QEMUBH *bh;
for (bh = async_context->first_bh; bh; bh = bh->next) {
if (!bh->deleted && bh->scheduled) {
if (bh->idle) {
/* idle bottom halves will be polled at least
* every 10ms */
*timeout = MIN(10, *timeout);
} else {
/* non-idle bottom halves will be executed
* immediately */
*timeout = 0;
break;
}
}
}
}
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