Annotation of qemu/linux-aio.c, revision 1.1.1.4

1.1       root        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 "block/raw-posix-aio.h"
                     13: 
                     14: #include <sys/eventfd.h>
                     15: #include <libaio.h>
                     16: 
                     17: /*
                     18:  * Queue size (per-device).
                     19:  *
                     20:  * XXX: eventually we need to communicate this to the guest and/or make it
                     21:  *      tunable by the guest.  If we get more outstanding requests at a time
                     22:  *      than this we will get EAGAIN from io_submit which is communicated to
                     23:  *      the guest as an I/O error.
                     24:  */
                     25: #define MAX_EVENTS 128
                     26: 
                     27: struct qemu_laiocb {
                     28:     BlockDriverAIOCB common;
                     29:     struct qemu_laio_state *ctx;
                     30:     struct iocb iocb;
                     31:     ssize_t ret;
                     32:     size_t nbytes;
1.1.1.3   root       33:     QEMUIOVector *qiov;
                     34:     bool is_read;
1.1       root       35:     QLIST_ENTRY(qemu_laiocb) node;
                     36: };
                     37: 
                     38: struct qemu_laio_state {
                     39:     io_context_t ctx;
                     40:     int efd;
                     41:     int count;
                     42: };
                     43: 
                     44: static inline ssize_t io_event_ret(struct io_event *ev)
                     45: {
                     46:     return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
                     47: }
                     48: 
                     49: /*
                     50:  * Completes an AIO request (calls the callback and frees the ACB).
                     51:  */
                     52: static void qemu_laio_process_completion(struct qemu_laio_state *s,
                     53:     struct qemu_laiocb *laiocb)
                     54: {
                     55:     int ret;
                     56: 
                     57:     s->count--;
                     58: 
                     59:     ret = laiocb->ret;
                     60:     if (ret != -ECANCELED) {
1.1.1.3   root       61:         if (ret == laiocb->nbytes) {
1.1       root       62:             ret = 0;
1.1.1.3   root       63:         } else if (ret >= 0) {
                     64:             /* Short reads mean EOF, pad with zeros. */
                     65:             if (laiocb->is_read) {
                     66:                 qemu_iovec_memset_skip(laiocb->qiov, 0,
                     67:                     laiocb->qiov->size - ret, ret);
                     68:             } else {
                     69:                 ret = -EINVAL;
                     70:             }
                     71:         }
1.1       root       72: 
                     73:         laiocb->common.cb(laiocb->common.opaque, ret);
                     74:     }
                     75: 
                     76:     qemu_aio_release(laiocb);
                     77: }
                     78: 
                     79: static void qemu_laio_completion_cb(void *opaque)
                     80: {
                     81:     struct qemu_laio_state *s = opaque;
                     82: 
                     83:     while (1) {
                     84:         struct io_event events[MAX_EVENTS];
                     85:         uint64_t val;
                     86:         ssize_t ret;
                     87:         struct timespec ts = { 0 };
                     88:         int nevents, i;
                     89: 
                     90:         do {
                     91:             ret = read(s->efd, &val, sizeof(val));
1.1.1.2   root       92:         } while (ret == -1 && errno == EINTR);
1.1       root       93: 
                     94:         if (ret == -1 && errno == EAGAIN)
                     95:             break;
                     96: 
                     97:         if (ret != 8)
                     98:             break;
                     99: 
                    100:         do {
                    101:             nevents = io_getevents(s->ctx, val, MAX_EVENTS, events, &ts);
                    102:         } while (nevents == -EINTR);
                    103: 
                    104:         for (i = 0; i < nevents; i++) {
                    105:             struct iocb *iocb = events[i].obj;
                    106:             struct qemu_laiocb *laiocb =
                    107:                     container_of(iocb, struct qemu_laiocb, iocb);
                    108: 
                    109:             laiocb->ret = io_event_ret(&events[i]);
1.1.1.3   root      110:             qemu_laio_process_completion(s, laiocb);
1.1       root      111:         }
                    112:     }
                    113: }
                    114: 
                    115: static int qemu_laio_flush_cb(void *opaque)
                    116: {
                    117:     struct qemu_laio_state *s = opaque;
                    118: 
                    119:     return (s->count > 0) ? 1 : 0;
                    120: }
                    121: 
                    122: static void laio_cancel(BlockDriverAIOCB *blockacb)
                    123: {
                    124:     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
                    125:     struct io_event event;
                    126:     int ret;
                    127: 
                    128:     if (laiocb->ret != -EINPROGRESS)
                    129:         return;
                    130: 
                    131:     /*
                    132:      * Note that as of Linux 2.6.31 neither the block device code nor any
                    133:      * filesystem implements cancellation of AIO request.
                    134:      * Thus the polling loop below is the normal code path.
                    135:      */
                    136:     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
                    137:     if (ret == 0) {
                    138:         laiocb->ret = -ECANCELED;
                    139:         return;
                    140:     }
                    141: 
                    142:     /*
                    143:      * We have to wait for the iocb to finish.
                    144:      *
                    145:      * The only way to get the iocb status update is by polling the io context.
                    146:      * We might be able to do this slightly more optimal by removing the
                    147:      * O_NONBLOCK flag.
                    148:      */
                    149:     while (laiocb->ret == -EINPROGRESS)
                    150:         qemu_laio_completion_cb(laiocb->ctx);
                    151: }
                    152: 
                    153: static AIOPool laio_pool = {
                    154:     .aiocb_size         = sizeof(struct qemu_laiocb),
                    155:     .cancel             = laio_cancel,
                    156: };
                    157: 
                    158: BlockDriverAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
                    159:         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
                    160:         BlockDriverCompletionFunc *cb, void *opaque, int type)
                    161: {
                    162:     struct qemu_laio_state *s = aio_ctx;
                    163:     struct qemu_laiocb *laiocb;
                    164:     struct iocb *iocbs;
                    165:     off_t offset = sector_num * 512;
                    166: 
                    167:     laiocb = qemu_aio_get(&laio_pool, bs, cb, opaque);
                    168:     laiocb->nbytes = nb_sectors * 512;
                    169:     laiocb->ctx = s;
                    170:     laiocb->ret = -EINPROGRESS;
1.1.1.3   root      171:     laiocb->is_read = (type == QEMU_AIO_READ);
                    172:     laiocb->qiov = qiov;
1.1       root      173: 
                    174:     iocbs = &laiocb->iocb;
                    175: 
                    176:     switch (type) {
                    177:     case QEMU_AIO_WRITE:
                    178:         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
                    179:        break;
                    180:     case QEMU_AIO_READ:
                    181:         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
                    182:        break;
1.1.1.3   root      183:     /* Currently Linux kernel does not support other operations */
1.1       root      184:     default:
                    185:         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
                    186:                         __func__, type);
                    187:         goto out_free_aiocb;
                    188:     }
                    189:     io_set_eventfd(&laiocb->iocb, s->efd);
                    190:     s->count++;
                    191: 
                    192:     if (io_submit(s->ctx, 1, &iocbs) < 0)
                    193:         goto out_dec_count;
                    194:     return &laiocb->common;
                    195: 
                    196: out_dec_count:
                    197:     s->count--;
1.1.1.3   root      198: out_free_aiocb:
                    199:     qemu_aio_release(laiocb);
1.1       root      200:     return NULL;
                    201: }
                    202: 
                    203: void *laio_init(void)
                    204: {
                    205:     struct qemu_laio_state *s;
                    206: 
1.1.1.3   root      207:     s = g_malloc0(sizeof(*s));
1.1       root      208:     s->efd = eventfd(0, 0);
                    209:     if (s->efd == -1)
                    210:         goto out_free_state;
                    211:     fcntl(s->efd, F_SETFL, O_NONBLOCK);
                    212: 
                    213:     if (io_setup(MAX_EVENTS, &s->ctx) != 0)
                    214:         goto out_close_efd;
                    215: 
                    216:     qemu_aio_set_fd_handler(s->efd, qemu_laio_completion_cb, NULL,
1.1.1.4 ! root      217:         qemu_laio_flush_cb, s);
1.1       root      218: 
                    219:     return s;
                    220: 
                    221: out_close_efd:
                    222:     close(s->efd);
                    223: out_free_state:
1.1.1.3   root      224:     g_free(s);
1.1       root      225:     return NULL;
                    226: }

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