xref: /openbmc/qemu/util/aio-wait.c (revision ed75658a)
1 /*
2  * AioContext wait support
3  *
4  * Copyright (C) 2018 Red Hat, Inc.
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a copy
7  * of this software and associated documentation files (the "Software"), to deal
8  * in the Software without restriction, including without limitation the rights
9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10  * copies of the Software, and to permit persons to whom the Software is
11  * furnished to do so, subject to the following conditions:
12  *
13  * The above copyright notice and this permission notice shall be included in
14  * all copies or substantial portions of the Software.
15  *
16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22  * THE SOFTWARE.
23  */
24 
25 #include "qemu/osdep.h"
26 #include "qemu/main-loop.h"
27 #include "block/aio-wait.h"
28 
29 AioWait global_aio_wait;
30 
31 static void dummy_bh_cb(void *opaque)
32 {
33     /* The point is to make AIO_WAIT_WHILE()'s aio_poll() return */
34 }
35 
36 void aio_wait_kick(void)
37 {
38     /*
39      * Paired with smp_mb in AIO_WAIT_WHILE. Here we have:
40      * write(condition);
41      * aio_wait_kick() {
42      *      smp_mb();
43      *      read(num_waiters);
44      * }
45      *
46      * And in AIO_WAIT_WHILE:
47      * write(num_waiters);
48      * smp_mb();
49      * read(condition);
50      */
51     smp_mb();
52 
53     if (qatomic_read(&global_aio_wait.num_waiters)) {
54         aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
55     }
56 }
57 
58 typedef struct {
59     bool done;
60     QEMUBHFunc *cb;
61     void *opaque;
62 } AioWaitBHData;
63 
64 /* Context: BH in IOThread */
65 static void aio_wait_bh(void *opaque)
66 {
67     AioWaitBHData *data = opaque;
68 
69     data->cb(data->opaque);
70 
71     data->done = true;
72     aio_wait_kick();
73 }
74 
75 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
76 {
77     AioWaitBHData data = {
78         .cb = cb,
79         .opaque = opaque,
80     };
81 
82     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
83 
84     aio_bh_schedule_oneshot(ctx, aio_wait_bh, &data);
85     AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done);
86 }
87