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