File:  [Qemu by Fabrice Bellard] / qemu / linux-aio.c
Revision 1.1.1.3 (vendor branch): download - view: text, annotated - select for diffs
Tue Apr 24 19:17:48 2018 UTC (2 years, 2 months ago) by root
Branches: qemu, MAIN
CVS tags: qemu1001, HEAD
qemu 1.0.1

    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_int.h"
   13: #include "block/raw-posix-aio.h"
   14: 
   15: #include <sys/eventfd.h>
   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:     int efd;
   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_skip(laiocb->qiov, 0,
   68:                     laiocb->qiov->size - ret, 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(void *opaque)
   81: {
   82:     struct qemu_laio_state *s = opaque;
   83: 
   84:     while (1) {
   85:         struct io_event events[MAX_EVENTS];
   86:         uint64_t val;
   87:         ssize_t ret;
   88:         struct timespec ts = { 0 };
   89:         int nevents, i;
   90: 
   91:         do {
   92:             ret = read(s->efd, &val, sizeof(val));
   93:         } while (ret == -1 && errno == EINTR);
   94: 
   95:         if (ret == -1 && errno == EAGAIN)
   96:             break;
   97: 
   98:         if (ret != 8)
   99:             break;
  100: 
  101:         do {
  102:             nevents = io_getevents(s->ctx, val, MAX_EVENTS, events, &ts);
  103:         } while (nevents == -EINTR);
  104: 
  105:         for (i = 0; i < nevents; i++) {
  106:             struct iocb *iocb = events[i].obj;
  107:             struct qemu_laiocb *laiocb =
  108:                     container_of(iocb, struct qemu_laiocb, iocb);
  109: 
  110:             laiocb->ret = io_event_ret(&events[i]);
  111:             qemu_laio_process_completion(s, laiocb);
  112:         }
  113:     }
  114: }
  115: 
  116: static int qemu_laio_flush_cb(void *opaque)
  117: {
  118:     struct qemu_laio_state *s = opaque;
  119: 
  120:     return (s->count > 0) ? 1 : 0;
  121: }
  122: 
  123: static void laio_cancel(BlockDriverAIOCB *blockacb)
  124: {
  125:     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
  126:     struct io_event event;
  127:     int ret;
  128: 
  129:     if (laiocb->ret != -EINPROGRESS)
  130:         return;
  131: 
  132:     /*
  133:      * Note that as of Linux 2.6.31 neither the block device code nor any
  134:      * filesystem implements cancellation of AIO request.
  135:      * Thus the polling loop below is the normal code path.
  136:      */
  137:     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
  138:     if (ret == 0) {
  139:         laiocb->ret = -ECANCELED;
  140:         return;
  141:     }
  142: 
  143:     /*
  144:      * We have to wait for the iocb to finish.
  145:      *
  146:      * The only way to get the iocb status update is by polling the io context.
  147:      * We might be able to do this slightly more optimal by removing the
  148:      * O_NONBLOCK flag.
  149:      */
  150:     while (laiocb->ret == -EINPROGRESS)
  151:         qemu_laio_completion_cb(laiocb->ctx);
  152: }
  153: 
  154: static AIOPool laio_pool = {
  155:     .aiocb_size         = sizeof(struct qemu_laiocb),
  156:     .cancel             = laio_cancel,
  157: };
  158: 
  159: BlockDriverAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
  160:         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
  161:         BlockDriverCompletionFunc *cb, void *opaque, int type)
  162: {
  163:     struct qemu_laio_state *s = aio_ctx;
  164:     struct qemu_laiocb *laiocb;
  165:     struct iocb *iocbs;
  166:     off_t offset = sector_num * 512;
  167: 
  168:     laiocb = qemu_aio_get(&laio_pool, bs, cb, opaque);
  169:     if (!laiocb)
  170:         return NULL;
  171:     laiocb->nbytes = nb_sectors * 512;
  172:     laiocb->ctx = s;
  173:     laiocb->ret = -EINPROGRESS;
  174:     laiocb->is_read = (type == QEMU_AIO_READ);
  175:     laiocb->qiov = qiov;
  176: 
  177:     iocbs = &laiocb->iocb;
  178: 
  179:     switch (type) {
  180:     case QEMU_AIO_WRITE:
  181:         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
  182: 	break;
  183:     case QEMU_AIO_READ:
  184:         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
  185: 	break;
  186:     /* Currently Linux kernel does not support other operations */
  187:     default:
  188:         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
  189:                         __func__, type);
  190:         goto out_free_aiocb;
  191:     }
  192:     io_set_eventfd(&laiocb->iocb, s->efd);
  193:     s->count++;
  194: 
  195:     if (io_submit(s->ctx, 1, &iocbs) < 0)
  196:         goto out_dec_count;
  197:     return &laiocb->common;
  198: 
  199: out_dec_count:
  200:     s->count--;
  201: out_free_aiocb:
  202:     qemu_aio_release(laiocb);
  203:     return NULL;
  204: }
  205: 
  206: void *laio_init(void)
  207: {
  208:     struct qemu_laio_state *s;
  209: 
  210:     s = g_malloc0(sizeof(*s));
  211:     s->efd = eventfd(0, 0);
  212:     if (s->efd == -1)
  213:         goto out_free_state;
  214:     fcntl(s->efd, F_SETFL, O_NONBLOCK);
  215: 
  216:     if (io_setup(MAX_EVENTS, &s->ctx) != 0)
  217:         goto out_close_efd;
  218: 
  219:     qemu_aio_set_fd_handler(s->efd, qemu_laio_completion_cb, NULL,
  220:         qemu_laio_flush_cb, NULL, s);
  221: 
  222:     return s;
  223: 
  224: out_close_efd:
  225:     close(s->efd);
  226: out_free_state:
  227:     g_free(s);
  228:     return NULL;
  229: }

unix.superglobalmegacorp.com