File:  [Qemu by Fabrice Bellard] / qemu / linux-aio.c
Revision 1.1.1.4 (vendor branch): download - view: text, annotated - select for diffs
Tue Apr 24 19:35:09 2018 UTC (2 years, 3 months ago) by root
Branches: qemu, MAIN
CVS tags: qemu1101, HEAD
qemu 1.1.1

    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/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;
   33:     QEMUIOVector *qiov;
   34:     bool is_read;
   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) {
   61:         if (ret == laiocb->nbytes) {
   62:             ret = 0;
   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:         }
   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));
   92:         } while (ret == -1 && errno == EINTR);
   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]);
  110:             qemu_laio_process_completion(s, laiocb);
  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;
  171:     laiocb->is_read = (type == QEMU_AIO_READ);
  172:     laiocb->qiov = qiov;
  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;
  183:     /* Currently Linux kernel does not support other operations */
  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--;
  198: out_free_aiocb:
  199:     qemu_aio_release(laiocb);
  200:     return NULL;
  201: }
  202: 
  203: void *laio_init(void)
  204: {
  205:     struct qemu_laio_state *s;
  206: 
  207:     s = g_malloc0(sizeof(*s));
  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,
  217:         qemu_laio_flush_cb, s);
  218: 
  219:     return s;
  220: 
  221: out_close_efd:
  222:     close(s->efd);
  223: out_free_state:
  224:     g_free(s);
  225:     return NULL;
  226: }

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