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 "qemu/osdep.h"
  15 #include "trace.h"
  16 #include "block/block_int.h"
  17 #include "block/blockjob_int.h"
  18 #include "qapi/error.h"
  19 #include "qapi/qmp/qerror.h"
  20 #include "qapi/qmp/qdict.h"
  21 #include "qemu/ratelimit.h"
  22 #include "sysemu/block-backend.h"
  23 #include "block/copy-on-read.h"
  24
  25 enum {
  26     /*
  27      * Maximum chunk size to feed to copy-on-read.  This should be
  28      * large enough to process multiple clusters in a single call, so
  29      * that populating contiguous regions of the image is efficient.
  30      */
  31     STREAM_CHUNK = 512 * 1024, /* in bytes */
  32 };
  33
  34 typedef struct StreamBlockJob {
  35     BlockJob common;
  36     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
  37     BlockDriverState *above_base;   /* Node directly above the base */
  38     BlockDriverState *cor_filter_bs;
  39     BlockDriverState *target_bs;
  40     BlockdevOnError on_error;
  41     char *backing_file_str;
  42     bool bs_read_only;
  43 } StreamBlockJob;
  44
  45 static int coroutine_fn stream_populate(BlockBackend *blk,
  46                                         int64_t offset, uint64_t bytes)
  47 {
  48     assert(bytes < SIZE_MAX);
  49
  50     return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
  51 }
  52
  53 static int stream_prepare(Job *job)
  54 {
  55     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  56     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
  57     BlockDriverState *base;
  58     BlockDriverState *unfiltered_base;
  59     Error *local_err = NULL;
  60     int ret = 0;
  61
  62     /* We should drop filter at this point, as filter hold the backing chain */
  63     bdrv_cor_filter_drop(s->cor_filter_bs);
  64     s->cor_filter_bs = NULL;
  65
  66     base = bdrv_filter_or_cow_bs(s->above_base);
  67     unfiltered_base = bdrv_skip_filters(base);
  68
  69     if (bdrv_cow_child(unfiltered_bs)) {
  70         const char *base_id = NULL, *base_fmt = NULL;
  71         if (unfiltered_base) {
  72             base_id = s->backing_file_str ?: unfiltered_base->filename;
  73             if (unfiltered_base->drv) {
  74                 base_fmt = unfiltered_base->drv->format_name;
  75             }
  76         }
  77         bdrv_set_backing_hd(unfiltered_bs, base, &local_err);
  78         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
  79         if (local_err) {
  80             error_report_err(local_err);
  81             return -EPERM;
  82         }
  83     }
  84
  85     return ret;
  86 }
  87
  88 static void stream_clean(Job *job)
  89 {
  90     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  91     BlockJob *bjob = &s->common;
  92
  93     if (s->cor_filter_bs) {
  94         bdrv_cor_filter_drop(s->cor_filter_bs);
  95         s->cor_filter_bs = NULL;
  96     }
  97
  98     /* Reopen the image back in read-only mode if necessary */
  99     if (s->bs_read_only) {
 100         /* Give up write permissions before making it read-only */
 101         blk_set_perm(bjob->blk, 0, BLK_PERM_ALL, &error_abort);
 102         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
 103     }
 104
 105     g_free(s->backing_file_str);
 106 }
 107
 108 static int coroutine_fn stream_run(Job *job, Error **errp)
 109 {
 110     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 111     BlockBackend *blk = s->common.blk;
 112     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
 113     int64_t len;
 114     int64_t offset = 0;
 115     uint64_t delay_ns = 0;
 116     int error = 0;
 117     int64_t n = 0; /* bytes */
 118
 119     if (unfiltered_bs == s->base_overlay) {
 120         /* Nothing to stream */
 121         return 0;
 122     }
 123
 124     len = bdrv_getlength(s->target_bs);
 125     if (len < 0) {
 126         return len;
 127     }
 128     job_progress_set_remaining(&s->common.job, len);
 129
 130     for ( ; offset < len; offset += n) {
 131         bool copy;
 132         int ret;
 133
 134         /* Note that even when no rate limit is applied we need to yield
 135          * with no pending I/O here so that bdrv_drain_all() returns.
 136          */
 137         job_sleep_ns(&s->common.job, delay_ns);
 138         if (job_is_cancelled(&s->common.job)) {
 139             break;
 140         }
 141
 142         copy = false;
 143
 144         ret = bdrv_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
 145         if (ret == 1) {
 146             /* Allocated in the top, no need to copy.  */
 147         } else if (ret >= 0) {
 148             /* Copy if allocated in the intermediate images.  Limit to the
 149              * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
 150             ret = bdrv_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
 151                                           s->base_overlay, true,
 152                                           offset, n, &n);
 153             /* Finish early if end of backing file has been reached */
 154             if (ret == 0 && n == 0) {
 155                 n = len - offset;
 156             }
 157
 158             copy = (ret > 0);
 159         }
 160         trace_stream_one_iteration(s, offset, n, ret);
 161         if (copy) {
 162             ret = stream_populate(blk, offset, n);
 163         }
 164         if (ret < 0) {
 165             BlockErrorAction action =
 166                 block_job_error_action(&s->common, s->on_error, true, -ret);
 167             if (action == BLOCK_ERROR_ACTION_STOP) {
 168                 n = 0;
 169                 continue;
 170             }
 171             if (error == 0) {
 172                 error = ret;
 173             }
 174             if (action == BLOCK_ERROR_ACTION_REPORT) {
 175                 break;
 176             }
 177         }
 178
 179         /* Publish progress */
 180         job_progress_update(&s->common.job, n);
 181         if (copy) {
 182             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 183         } else {
 184             delay_ns = 0;
 185         }
 186     }
 187
 188     /* Do not remove the backing file if an error was there but ignored. */
 189     return error;
 190 }
 191
 192 static const BlockJobDriver stream_job_driver = {
 193     .job_driver = {
 194         .instance_size = sizeof(StreamBlockJob),
 195         .job_type      = JOB_TYPE_STREAM,
 196         .free          = block_job_free,
 197         .run           = stream_run,
 198         .prepare       = stream_prepare,
 199         .clean         = stream_clean,
 200         .user_resume   = block_job_user_resume,
 201     },
 202 };
 203
 204 void stream_start(const char *job_id, BlockDriverState *bs,
 205                   BlockDriverState *base, const char *backing_file_str,
 206                   BlockDriverState *bottom,
 207                   int creation_flags, int64_t speed,
 208                   BlockdevOnError on_error,
 209                   const char *filter_node_name,
 210                   Error **errp)
 211 {
 212     StreamBlockJob *s = NULL;
 213     BlockDriverState *iter;
 214     bool bs_read_only;
 215     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 216     BlockDriverState *base_overlay;
 217     BlockDriverState *cor_filter_bs = NULL;
 218     BlockDriverState *above_base;
 219     QDict *opts;
 220     int ret;
 221
 222     assert(!(base && bottom));
 223     assert(!(backing_file_str && bottom));
 224
 225     if (bottom) {
 226         /*
 227          * New simple interface. The code is written in terms of old interface
 228          * with @base parameter (still, it doesn't freeze link to base, so in
 229          * this mean old code is correct for new interface). So, for now, just
 230          * emulate base_overlay and above_base. Still, when old interface
 231          * finally removed, we should refactor code to use only "bottom", but
 232          * not "*base*" things.
 233          */
 234         assert(!bottom->drv->is_filter);
 235         base_overlay = above_base = bottom;
 236     } else {
 237         base_overlay = bdrv_find_overlay(bs, base);
 238         if (!base_overlay) {
 239             error_setg(errp, "'%s' is not in the backing chain of '%s'",
 240                        base->node_name, bs->node_name);
 241             return;
 242         }
 243
 244         /*
 245          * Find the node directly above @base.  @base_overlay is a COW overlay,
 246          * so it must have a bdrv_cow_child(), but it is the immediate overlay
 247          * of @base, so between the two there can only be filters.
 248          */
 249         above_base = base_overlay;
 250         if (bdrv_cow_bs(above_base) != base) {
 251             above_base = bdrv_cow_bs(above_base);
 252             while (bdrv_filter_bs(above_base) != base) {
 253                 above_base = bdrv_filter_bs(above_base);
 254             }
 255         }
 256     }
 257
 258     /* Make sure that the image is opened in read-write mode */
 259     bs_read_only = bdrv_is_read_only(bs);
 260     if (bs_read_only) {
 261         int ret;
 262         /* Hold the chain during reopen */
 263         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
 264             return;
 265         }
 266
 267         ret = bdrv_reopen_set_read_only(bs, false, errp);
 268
 269         /* failure, or cor-filter will hold the chain */
 270         bdrv_unfreeze_backing_chain(bs, above_base);
 271
 272         if (ret < 0) {
 273             return;
 274         }
 275     }
 276
 277     opts = qdict_new();
 278
 279     qdict_put_str(opts, "driver", "copy-on-read");
 280     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
 281     /* Pass the base_overlay node name as 'bottom' to COR driver */
 282     qdict_put_str(opts, "bottom", base_overlay->node_name);
 283     if (filter_node_name) {
 284         qdict_put_str(opts, "node-name", filter_node_name);
 285     }
 286
 287     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
 288     if (!cor_filter_bs) {
 289         goto fail;
 290     }
 291
 292     if (!filter_node_name) {
 293         cor_filter_bs->implicit = true;
 294     }
 295
 296     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
 297                          BLK_PERM_CONSISTENT_READ,
 298                          basic_flags | BLK_PERM_WRITE,
 299                          speed, creation_flags, NULL, NULL, errp);
 300     if (!s) {
 301         goto fail;
 302     }
 303
 304     /*
 305      * Prevent concurrent jobs trying to modify the graph structure here, we
 306      * already have our own plans. Also don't allow resize as the image size is
 307      * queried only at the job start and then cached.
 308      */
 309     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
 310                            basic_flags | BLK_PERM_WRITE, errp)) {
 311         goto fail;
 312     }
 313
 314     /* Block all intermediate nodes between bs and base, because they will
 315      * disappear from the chain after this operation. The streaming job reads
 316      * every block only once, assuming that it doesn't change, so forbid writes
 317      * and resizes. Reassign the base node pointer because the backing BS of the
 318      * bottom node might change after the call to bdrv_reopen_set_read_only()
 319      * due to parallel block jobs running.
 320      * above_base node might change after the call to
 321      * bdrv_reopen_set_read_only() due to parallel block jobs running.
 322      */
 323     base = bdrv_filter_or_cow_bs(above_base);
 324     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
 325          iter = bdrv_filter_or_cow_bs(iter))
 326     {
 327         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 328                                  basic_flags, errp);
 329         if (ret < 0) {
 330             goto fail;
 331         }
 332     }
 333
 334     s->base_overlay = base_overlay;
 335     s->above_base = above_base;
 336     s->backing_file_str = g_strdup(backing_file_str);
 337     s->cor_filter_bs = cor_filter_bs;
 338     s->target_bs = bs;
 339     s->bs_read_only = bs_read_only;
 340
 341     s->on_error = on_error;
 342     trace_stream_start(bs, base, s);
 343     job_start(&s->common.job);
 344     return;
 345
 346 fail:
 347     if (s) {
 348         job_early_fail(&s->common.job);
 349     }
 350     if (cor_filter_bs) {
 351         bdrv_cor_filter_drop(cor_filter_bs);
 352     }
 353     if (bs_read_only) {
 354         bdrv_reopen_set_read_only(bs, true, NULL);
 355     }
 356 }