xref: /openbmc/qemu/block/linux-aio.c (revision 1f32989d)
1 /*
2  * Linux native AIO support.
3  *
4  * Copyright (C) 2009 IBM, Corp.
5  * Copyright (C) 2009 Red Hat, Inc.
6  *
7  * This work is licensed under the terms of the GNU GPL, version 2 or later.
8  * See the COPYING file in the top-level directory.
9  */
10 #include "qemu-common.h"
11 #include "qemu-aio.h"
12 #include "qemu-queue.h"
13 #include "block/raw-aio.h"
14 #include "event_notifier.h"
15 
16 #include <libaio.h>
17 
18 /*
19  * Queue size (per-device).
20  *
21  * XXX: eventually we need to communicate this to the guest and/or make it
22  *      tunable by the guest.  If we get more outstanding requests at a time
23  *      than this we will get EAGAIN from io_submit which is communicated to
24  *      the guest as an I/O error.
25  */
26 #define MAX_EVENTS 128
27 
28 struct qemu_laiocb {
29     BlockDriverAIOCB common;
30     struct qemu_laio_state *ctx;
31     struct iocb iocb;
32     ssize_t ret;
33     size_t nbytes;
34     QEMUIOVector *qiov;
35     bool is_read;
36     QLIST_ENTRY(qemu_laiocb) node;
37 };
38 
39 struct qemu_laio_state {
40     io_context_t ctx;
41     EventNotifier e;
42     int count;
43 };
44 
45 static inline ssize_t io_event_ret(struct io_event *ev)
46 {
47     return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
48 }
49 
50 /*
51  * Completes an AIO request (calls the callback and frees the ACB).
52  */
53 static void qemu_laio_process_completion(struct qemu_laio_state *s,
54     struct qemu_laiocb *laiocb)
55 {
56     int ret;
57 
58     s->count--;
59 
60     ret = laiocb->ret;
61     if (ret != -ECANCELED) {
62         if (ret == laiocb->nbytes) {
63             ret = 0;
64         } else if (ret >= 0) {
65             /* Short reads mean EOF, pad with zeros. */
66             if (laiocb->is_read) {
67                 qemu_iovec_memset(laiocb->qiov, ret, 0,
68                     laiocb->qiov->size - ret);
69             } else {
70                 ret = -EINVAL;
71             }
72         }
73 
74         laiocb->common.cb(laiocb->common.opaque, ret);
75     }
76 
77     qemu_aio_release(laiocb);
78 }
79 
80 static void qemu_laio_completion_cb(EventNotifier *e)
81 {
82     struct qemu_laio_state *s = container_of(e, struct qemu_laio_state, e);
83 
84     while (event_notifier_test_and_clear(&s->e)) {
85         struct io_event events[MAX_EVENTS];
86         struct timespec ts = { 0 };
87         int nevents, i;
88 
89         do {
90             nevents = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS, events, &ts);
91         } while (nevents == -EINTR);
92 
93         for (i = 0; i < nevents; i++) {
94             struct iocb *iocb = events[i].obj;
95             struct qemu_laiocb *laiocb =
96                     container_of(iocb, struct qemu_laiocb, iocb);
97 
98             laiocb->ret = io_event_ret(&events[i]);
99             qemu_laio_process_completion(s, laiocb);
100         }
101     }
102 }
103 
104 static int qemu_laio_flush_cb(EventNotifier *e)
105 {
106     struct qemu_laio_state *s = container_of(e, struct qemu_laio_state, e);
107 
108     return (s->count > 0) ? 1 : 0;
109 }
110 
111 static void laio_cancel(BlockDriverAIOCB *blockacb)
112 {
113     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
114     struct io_event event;
115     int ret;
116 
117     if (laiocb->ret != -EINPROGRESS)
118         return;
119 
120     /*
121      * Note that as of Linux 2.6.31 neither the block device code nor any
122      * filesystem implements cancellation of AIO request.
123      * Thus the polling loop below is the normal code path.
124      */
125     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
126     if (ret == 0) {
127         laiocb->ret = -ECANCELED;
128         return;
129     }
130 
131     /*
132      * We have to wait for the iocb to finish.
133      *
134      * The only way to get the iocb status update is by polling the io context.
135      * We might be able to do this slightly more optimal by removing the
136      * O_NONBLOCK flag.
137      */
138     while (laiocb->ret == -EINPROGRESS) {
139         qemu_laio_completion_cb(&laiocb->ctx->e);
140     }
141 }
142 
143 static const AIOCBInfo laio_aiocb_info = {
144     .aiocb_size         = sizeof(struct qemu_laiocb),
145     .cancel             = laio_cancel,
146 };
147 
148 BlockDriverAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
149         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
150         BlockDriverCompletionFunc *cb, void *opaque, int type)
151 {
152     struct qemu_laio_state *s = aio_ctx;
153     struct qemu_laiocb *laiocb;
154     struct iocb *iocbs;
155     off_t offset = sector_num * 512;
156 
157     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
158     laiocb->nbytes = nb_sectors * 512;
159     laiocb->ctx = s;
160     laiocb->ret = -EINPROGRESS;
161     laiocb->is_read = (type == QEMU_AIO_READ);
162     laiocb->qiov = qiov;
163 
164     iocbs = &laiocb->iocb;
165 
166     switch (type) {
167     case QEMU_AIO_WRITE:
168         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
169 	break;
170     case QEMU_AIO_READ:
171         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
172 	break;
173     /* Currently Linux kernel does not support other operations */
174     default:
175         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
176                         __func__, type);
177         goto out_free_aiocb;
178     }
179     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
180     s->count++;
181 
182     if (io_submit(s->ctx, 1, &iocbs) < 0)
183         goto out_dec_count;
184     return &laiocb->common;
185 
186 out_dec_count:
187     s->count--;
188 out_free_aiocb:
189     qemu_aio_release(laiocb);
190     return NULL;
191 }
192 
193 void *laio_init(void)
194 {
195     struct qemu_laio_state *s;
196 
197     s = g_malloc0(sizeof(*s));
198     if (event_notifier_init(&s->e, false) < 0) {
199         goto out_free_state;
200     }
201 
202     if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
203         goto out_close_efd;
204     }
205 
206     qemu_aio_set_event_notifier(&s->e, qemu_laio_completion_cb,
207                                 qemu_laio_flush_cb);
208 
209     return s;
210 
211 out_close_efd:
212     event_notifier_cleanup(&s->e);
213 out_free_state:
214     g_free(s);
215     return NULL;
216 }
217