async: Remove AsyncContext
The purpose of AsyncContexts was to protect qcow and qcow2 against reentrancy
during an emulated bdrv_read/write (which includes a qemu_aio_wait() call and
can run AIO callbacks of different requests if it weren't for AsyncContexts).
Now both qcow and qcow2 are protected by CoMutexes and AsyncContexts can be
removed.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/async.c b/async.c
index fd313df..3fe70b9 100644
--- a/async.c
+++ b/async.c
@@ -25,92 +25,8 @@
#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;
-}
+/* Anchor of the list of Bottom Halves belonging to the context */
+static struct QEMUBH *first_bh;
/***********************************************************/
/* bottom halves (can be seen as timers which expire ASAP) */
@@ -130,8 +46,8 @@
bh = qemu_mallocz(sizeof(QEMUBH));
bh->cb = cb;
bh->opaque = opaque;
- bh->next = async_context->first_bh;
- async_context->first_bh = bh;
+ bh->next = first_bh;
+ first_bh = bh;
return bh;
}
@@ -141,7 +57,7 @@
int ret;
ret = 0;
- for (bh = async_context->first_bh; bh; bh = next) {
+ for (bh = first_bh; bh; bh = next) {
next = bh->next;
if (!bh->deleted && bh->scheduled) {
bh->scheduled = 0;
@@ -153,7 +69,7 @@
}
/* remove deleted bhs */
- bhp = &async_context->first_bh;
+ bhp = &first_bh;
while (*bhp) {
bh = *bhp;
if (bh->deleted) {
@@ -199,7 +115,7 @@
{
QEMUBH *bh;
- for (bh = async_context->first_bh; bh; bh = bh->next) {
+ for (bh = first_bh; bh; bh = bh->next) {
if (!bh->deleted && bh->scheduled) {
if (bh->idle) {
/* idle bottom halves will be polled at least
