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/qdict.h"
  20 #include "qemu/ratelimit.h"
  21 #include "sysemu/block-backend.h"
  22 #include "block/copy-on-read.h"
  23
  24 enum {
  25     /*
  26      * Maximum chunk size to feed to copy-on-read.  This should be
  27      * large enough to process multiple clusters in a single call, so
  28      * that populating contiguous regions of the image is efficient.
  29      */
  30     STREAM_CHUNK = 512 * 1024, /* in bytes */
  31 };
  32
  33 typedef struct StreamBlockJob {
  34     BlockJob common;
  35     BlockBackend *blk;
  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 *unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
  58     BlockDriverState *base;
  59     BlockDriverState *unfiltered_base;
  60     Error *local_err = NULL;
  61     int ret = 0;
  62
  63     GLOBAL_STATE_CODE();
  64
  65     /* We should drop filter at this point, as filter hold the backing chain */
  66     bdrv_cor_filter_drop(s->cor_filter_bs);
  67     s->cor_filter_bs = NULL;
  68
  69     /*
  70      * bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
  71      * of unfiltered_bs is drained. Drain already here and use
  72      * bdrv_set_backing_hd_drained() instead because the polling during
  73      * drained_begin() might change the graph, and if we do this only later, we
  74      * may end up working with the wrong base node (or it might even have gone
  75      * away by the time we want to use it).
  76      */
  77     bdrv_drained_begin(unfiltered_bs);
  78     if (unfiltered_bs_cow) {
  79         bdrv_ref(unfiltered_bs_cow);
  80         bdrv_drained_begin(unfiltered_bs_cow);
  81     }
  82
  83     bdrv_graph_rdlock_main_loop();
  84     base = bdrv_filter_or_cow_bs(s->above_base);
  85     unfiltered_base = bdrv_skip_filters(base);
  86     bdrv_graph_rdunlock_main_loop();
  87
  88     if (bdrv_cow_child(unfiltered_bs)) {
  89         const char *base_id = NULL, *base_fmt = NULL;
  90         if (unfiltered_base) {
  91             base_id = s->backing_file_str ?: unfiltered_base->filename;
  92             if (unfiltered_base->drv) {
  93                 base_fmt = unfiltered_base->drv->format_name;
  94             }
  95         }
  96
  97         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
  98
  99         /*
 100          * This call will do I/O, so the graph can change again from here on.
 101          * We have already completed the graph change, so we are not in danger
 102          * of operating on the wrong node any more if this happens.
 103          */
 104         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
 105         if (local_err) {
 106             error_report_err(local_err);
 107             ret = -EPERM;
 108             goto out;
 109         }
 110     }
 111
 112 out:
 113     if (unfiltered_bs_cow) {
 114         bdrv_drained_end(unfiltered_bs_cow);
 115         bdrv_unref(unfiltered_bs_cow);
 116     }
 117     bdrv_drained_end(unfiltered_bs);
 118     return ret;
 119 }
 120
 121 static void stream_clean(Job *job)
 122 {
 123     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 124
 125     if (s->cor_filter_bs) {
 126         bdrv_cor_filter_drop(s->cor_filter_bs);
 127         s->cor_filter_bs = NULL;
 128     }
 129
 130     blk_unref(s->blk);
 131     s->blk = NULL;
 132
 133     /* Reopen the image back in read-only mode if necessary */
 134     if (s->bs_read_only) {
 135         /* Give up write permissions before making it read-only */
 136         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
 137     }
 138
 139     g_free(s->backing_file_str);
 140 }
 141
 142 static int coroutine_fn stream_run(Job *job, Error **errp)
 143 {
 144     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 145     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
 146     int64_t len;
 147     int64_t offset = 0;
 148     int error = 0;
 149     int64_t n = 0; /* bytes */
 150
 151     if (unfiltered_bs == s->base_overlay) {
 152         /* Nothing to stream */
 153         return 0;
 154     }
 155
 156     WITH_GRAPH_RDLOCK_GUARD() {
 157         len = bdrv_co_getlength(s->target_bs);
 158         if (len < 0) {
 159             return len;
 160         }
 161     }
 162     job_progress_set_remaining(&s->common.job, len);
 163
 164     for ( ; offset < len; offset += n) {
 165         bool copy;
 166         int ret;
 167
 168         /* Note that even when no rate limit is applied we need to yield
 169          * with no pending I/O here so that bdrv_drain_all() returns.
 170          */
 171         block_job_ratelimit_sleep(&s->common);
 172         if (job_is_cancelled(&s->common.job)) {
 173             break;
 174         }
 175
 176         copy = false;
 177
 178         WITH_GRAPH_RDLOCK_GUARD() {
 179             ret = bdrv_co_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
 180             if (ret == 1) {
 181                 /* Allocated in the top, no need to copy.  */
 182             } else if (ret >= 0) {
 183                 /*
 184                  * Copy if allocated in the intermediate images.  Limit to the
 185                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
 186                  */
 187                 ret = bdrv_co_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
 188                                                  s->base_overlay, true,
 189                                                  offset, n, &n);
 190                 /* Finish early if end of backing file has been reached */
 191                 if (ret == 0 && n == 0) {
 192                     n = len - offset;
 193                 }
 194
 195                 copy = (ret > 0);
 196             }
 197         }
 198         trace_stream_one_iteration(s, offset, n, ret);
 199         if (copy) {
 200             ret = stream_populate(s->blk, offset, n);
 201         }
 202         if (ret < 0) {
 203             BlockErrorAction action =
 204                 block_job_error_action(&s->common, s->on_error, true, -ret);
 205             if (action == BLOCK_ERROR_ACTION_STOP) {
 206                 n = 0;
 207                 continue;
 208             }
 209             if (error == 0) {
 210                 error = ret;
 211             }
 212             if (action == BLOCK_ERROR_ACTION_REPORT) {
 213                 break;
 214             }
 215         }
 216
 217         /* Publish progress */
 218         job_progress_update(&s->common.job, n);
 219         if (copy) {
 220             block_job_ratelimit_processed_bytes(&s->common, n);
 221         }
 222     }
 223
 224     /* Do not remove the backing file if an error was there but ignored. */
 225     return error;
 226 }
 227
 228 static const BlockJobDriver stream_job_driver = {
 229     .job_driver = {
 230         .instance_size = sizeof(StreamBlockJob),
 231         .job_type      = JOB_TYPE_STREAM,
 232         .free          = block_job_free,
 233         .run           = stream_run,
 234         .prepare       = stream_prepare,
 235         .clean         = stream_clean,
 236         .user_resume   = block_job_user_resume,
 237     },
 238 };
 239
 240 void stream_start(const char *job_id, BlockDriverState *bs,
 241                   BlockDriverState *base, const char *backing_file_str,
 242                   BlockDriverState *bottom,
 243                   int creation_flags, int64_t speed,
 244                   BlockdevOnError on_error,
 245                   const char *filter_node_name,
 246                   Error **errp)
 247 {
 248     StreamBlockJob *s = NULL;
 249     BlockDriverState *iter;
 250     bool bs_read_only;
 251     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 252     BlockDriverState *base_overlay;
 253     BlockDriverState *cor_filter_bs = NULL;
 254     BlockDriverState *above_base;
 255     QDict *opts;
 256     int ret;
 257
 258     GLOBAL_STATE_CODE();
 259
 260     assert(!(base && bottom));
 261     assert(!(backing_file_str && bottom));
 262
 263     if (bottom) {
 264         /*
 265          * New simple interface. The code is written in terms of old interface
 266          * with @base parameter (still, it doesn't freeze link to base, so in
 267          * this mean old code is correct for new interface). So, for now, just
 268          * emulate base_overlay and above_base. Still, when old interface
 269          * finally removed, we should refactor code to use only "bottom", but
 270          * not "*base*" things.
 271          */
 272         assert(!bottom->drv->is_filter);
 273         base_overlay = above_base = bottom;
 274     } else {
 275         GRAPH_RDLOCK_GUARD_MAINLOOP();
 276
 277         base_overlay = bdrv_find_overlay(bs, base);
 278         if (!base_overlay) {
 279             error_setg(errp, "'%s' is not in the backing chain of '%s'",
 280                        base->node_name, bs->node_name);
 281             return;
 282         }
 283
 284         /*
 285          * Find the node directly above @base.  @base_overlay is a COW overlay,
 286          * so it must have a bdrv_cow_child(), but it is the immediate overlay
 287          * of @base, so between the two there can only be filters.
 288          */
 289         above_base = base_overlay;
 290         if (bdrv_cow_bs(above_base) != base) {
 291             above_base = bdrv_cow_bs(above_base);
 292             while (bdrv_filter_bs(above_base) != base) {
 293                 above_base = bdrv_filter_bs(above_base);
 294             }
 295         }
 296     }
 297
 298     /* Make sure that the image is opened in read-write mode */
 299     bs_read_only = bdrv_is_read_only(bs);
 300     if (bs_read_only) {
 301         /* Hold the chain during reopen */
 302         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
 303             return;
 304         }
 305
 306         ret = bdrv_reopen_set_read_only(bs, false, errp);
 307
 308         /* failure, or cor-filter will hold the chain */
 309         bdrv_unfreeze_backing_chain(bs, above_base);
 310
 311         if (ret < 0) {
 312             return;
 313         }
 314     }
 315
 316     opts = qdict_new();
 317
 318     qdict_put_str(opts, "driver", "copy-on-read");
 319     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
 320     /* Pass the base_overlay node name as 'bottom' to COR driver */
 321     qdict_put_str(opts, "bottom", base_overlay->node_name);
 322     if (filter_node_name) {
 323         qdict_put_str(opts, "node-name", filter_node_name);
 324     }
 325
 326     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
 327     if (!cor_filter_bs) {
 328         goto fail;
 329     }
 330
 331     if (!filter_node_name) {
 332         cor_filter_bs->implicit = true;
 333     }
 334
 335     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
 336                          0, BLK_PERM_ALL,
 337                          speed, creation_flags, NULL, NULL, errp);
 338     if (!s) {
 339         goto fail;
 340     }
 341
 342     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
 343                              basic_flags | BLK_PERM_WRITE, errp);
 344     if (!s->blk) {
 345         goto fail;
 346     }
 347     /*
 348      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
 349      * The job reports that it's busy until it reaches a pause point.
 350      */
 351     blk_set_disable_request_queuing(s->blk, true);
 352     blk_set_allow_aio_context_change(s->blk, true);
 353
 354     /*
 355      * Prevent concurrent jobs trying to modify the graph structure here, we
 356      * already have our own plans. Also don't allow resize as the image size is
 357      * queried only at the job start and then cached.
 358      */
 359     bdrv_graph_wrlock(bs);
 360     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
 361                            basic_flags | BLK_PERM_WRITE, errp)) {
 362         bdrv_graph_wrunlock();
 363         goto fail;
 364     }
 365
 366     /* Block all intermediate nodes between bs and base, because they will
 367      * disappear from the chain after this operation. The streaming job reads
 368      * every block only once, assuming that it doesn't change, so forbid writes
 369      * and resizes. Reassign the base node pointer because the backing BS of the
 370      * bottom node might change after the call to bdrv_reopen_set_read_only()
 371      * due to parallel block jobs running.
 372      * above_base node might change after the call to
 373      * bdrv_reopen_set_read_only() due to parallel block jobs running.
 374      */
 375     base = bdrv_filter_or_cow_bs(above_base);
 376     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
 377          iter = bdrv_filter_or_cow_bs(iter))
 378     {
 379         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 380                                  basic_flags, errp);
 381         if (ret < 0) {
 382             bdrv_graph_wrunlock();
 383             goto fail;
 384         }
 385     }
 386     bdrv_graph_wrunlock();
 387
 388     s->base_overlay = base_overlay;
 389     s->above_base = above_base;
 390     s->backing_file_str = g_strdup(backing_file_str);
 391     s->cor_filter_bs = cor_filter_bs;
 392     s->target_bs = bs;
 393     s->bs_read_only = bs_read_only;
 394
 395     s->on_error = on_error;
 396     trace_stream_start(bs, base, s);
 397     job_start(&s->common.job);
 398     return;
 399
 400 fail:
 401     if (s) {
 402         job_early_fail(&s->common.job);
 403     }
 404     if (cor_filter_bs) {
 405         bdrv_cor_filter_drop(cor_filter_bs);
 406     }
 407     if (bs_read_only) {
 408         bdrv_reopen_set_read_only(bs, true, NULL);
 409     }
 410 }