block/stream.c

   1 /*
   2  * Image streaming
   3  *
   4  * Copyright IBM, Corp. 2011
   5  *
   6  * Authors:
   7  *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  10  * See the COPYING.LIB file in the top-level directory.
  11  *
  12  */
  13
  14 #include "trace.h"
  15 #include "block_int.h"
  16 #include "qemu/ratelimit.h"
  17
  18 enum {
  19     /*
  20      * Size of data buffer for populating the image file.  This should be large
  21      * enough to process multiple clusters in a single call, so that populating
  22      * contiguous regions of the image is efficient.
  23      */
  24     STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */
  25 };
  26
  27 #define SLICE_TIME 100000000ULL /* ns */
  28
  29 typedef struct StreamBlockJob {
  30     BlockJob common;
  31     RateLimit limit;
  32     BlockDriverState *base;
  33     char backing_file_id[1024];
  34 } StreamBlockJob;
  35
  36 static int coroutine_fn stream_populate(BlockDriverState *bs,
  37                                         int64_t sector_num, int nb_sectors,
  38                                         void *buf)
  39 {
  40     struct iovec iov = {
  41         .iov_base = buf,
  42         .iov_len  = nb_sectors * BDRV_SECTOR_SIZE,
  43     };
  44     QEMUIOVector qiov;
  45
  46     qemu_iovec_init_external(&qiov, &iov, 1);
  47
  48     /* Copy-on-read the unallocated clusters */
  49     return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);
  50 }
  51
  52 static void close_unused_images(BlockDriverState *top, BlockDriverState *base,
  53                                 const char *base_id)
  54 {
  55     BlockDriverState *intermediate;
  56     intermediate = top->backing_hd;
  57
  58     while (intermediate) {
  59         BlockDriverState *unused;
  60
  61         /* reached base */
  62         if (intermediate == base) {
  63             break;
  64         }
  65
  66         unused = intermediate;
  67         intermediate = intermediate->backing_hd;
  68         unused->backing_hd = NULL;
  69         bdrv_delete(unused);
  70     }
  71     top->backing_hd = base;
  72 }
  73
  74 static void coroutine_fn stream_run(void *opaque)
  75 {
  76     StreamBlockJob *s = opaque;
  77     BlockDriverState *bs = s->common.bs;
  78     BlockDriverState *base = s->base;
  79     int64_t sector_num, end;
  80     int ret = 0;
  81     int n = 0;
  82     void *buf;
  83
  84     s->common.len = bdrv_getlength(bs);
  85     if (s->common.len < 0) {
  86         block_job_complete(&s->common, s->common.len);
  87         return;
  88     }
  89
  90     end = s->common.len >> BDRV_SECTOR_BITS;
  91     buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);
  92
  93     /* Turn on copy-on-read for the whole block device so that guest read
  94      * requests help us make progress.  Only do this when copying the entire
  95      * backing chain since the copy-on-read operation does not take base into
  96      * account.
  97      */
  98     if (!base) {
  99         bdrv_enable_copy_on_read(bs);
 100     }
 101
 102     for (sector_num = 0; sector_num < end; sector_num += n) {
 103         uint64_t delay_ns = 0;
 104         bool copy;
 105
 106 wait:
 107         /* Note that even when no rate limit is applied we need to yield
 108          * with no pending I/O here so that qemu_aio_flush() returns.
 109          */
 110         block_job_sleep_ns(&s->common, rt_clock, delay_ns);
 111         if (block_job_is_cancelled(&s->common)) {
 112             break;
 113         }
 114
 115         ret = bdrv_co_is_allocated(bs, sector_num,
 116                                    STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);
 117         if (ret == 1) {
 118             /* Allocated in the top, no need to copy.  */
 119             copy = false;
 120         } else {
 121             /* Copy if allocated in the intermediate images.  Limit to the
 122              * known-unallocated area [sector_num, sector_num+n).  */
 123             ret = bdrv_co_is_allocated_above(bs->backing_hd, base,
 124                                              sector_num, n, &n);
 125             copy = (ret == 1);
 126         }
 127         trace_stream_one_iteration(s, sector_num, n, ret);
 128         if (ret >= 0 && copy) {
 129             if (s->common.speed) {
 130                 delay_ns = ratelimit_calculate_delay(&s->limit, n);
 131                 if (delay_ns > 0) {
 132                     goto wait;
 133                 }
 134             }
 135             ret = stream_populate(bs, sector_num, n, buf);
 136         }
 137         if (ret < 0) {
 138             break;
 139         }
 140         ret = 0;
 141
 142         /* Publish progress */
 143         s->common.offset += n * BDRV_SECTOR_SIZE;
 144     }
 145
 146     if (!base) {
 147         bdrv_disable_copy_on_read(bs);
 148     }
 149
 150     if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {
 151         const char *base_id = NULL, *base_fmt = NULL;
 152         if (base) {
 153             base_id = s->backing_file_id;
 154             if (base->drv) {
 155                 base_fmt = base->drv->format_name;
 156             }
 157         }
 158         ret = bdrv_change_backing_file(bs, base_id, base_fmt);
 159         close_unused_images(bs, base, base_id);
 160     }
 161
 162     qemu_vfree(buf);
 163     block_job_complete(&s->common, ret);
 164 }
 165
 166 static void stream_set_speed(BlockJob *job, int64_t speed, Error **errp)
 167 {
 168     StreamBlockJob *s = container_of(job, StreamBlockJob, common);
 169
 170     if (speed < 0) {
 171         error_set(errp, QERR_INVALID_PARAMETER, "speed");
 172         return;
 173     }
 174     ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
 175 }
 176
 177 static BlockJobType stream_job_type = {
 178     .instance_size = sizeof(StreamBlockJob),
 179     .job_type      = "stream",
 180     .set_speed     = stream_set_speed,
 181 };
 182
 183 void stream_start(BlockDriverState *bs, BlockDriverState *base,
 184                   const char *base_id, int64_t speed,
 185                   BlockDriverCompletionFunc *cb,
 186                   void *opaque, Error **errp)
 187 {
 188     StreamBlockJob *s;
 189
 190     s = block_job_create(&stream_job_type, bs, speed, cb, opaque, errp);
 191     if (!s) {
 192         return;
 193     }
 194
 195     s->base = base;
 196     if (base_id) {
 197         pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);
 198     }
 199
 200     s->common.co = qemu_coroutine_create(stream_run);
 201     trace_stream_start(bs, base, s, s->common.co, opaque);
 202     qemu_coroutine_enter(s->common.co, s);
 203 }