block/backup-top.c

   1 /*
   2  * backup-top filter driver
   3  *
   4  * The driver performs Copy-Before-Write (CBW) operation: it is injected above
   5  * some node, and before each write it copies _old_ data to the target node.
   6  *
   7  * Copyright (c) 2018-2019 Virtuozzo International GmbH.
   8  *
   9  * Author:
  10  *  Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  24  */
  25
  26 #include "qemu/osdep.h"
  27
  28 #include "sysemu/block-backend.h"
  29 #include "qemu/cutils.h"
  30 #include "qapi/error.h"
  31 #include "block/block_int.h"
  32 #include "block/qdict.h"
  33 #include "block/block-copy.h"
  34
  35 #include "block/backup-top.h"
  36
  37 typedef struct BDRVBackupTopState {
  38     BlockCopyState *bcs;
  39     BdrvChild *target;
  40     bool active;
  41     int64_t cluster_size;
  42 } BDRVBackupTopState;
  43
  44 static coroutine_fn int backup_top_co_preadv(
  45         BlockDriverState *bs, uint64_t offset, uint64_t bytes,
  46         QEMUIOVector *qiov, int flags)
  47 {
  48     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
  49 }
  50
  51 static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
  52                                        uint64_t bytes, BdrvRequestFlags flags)
  53 {
  54     BDRVBackupTopState *s = bs->opaque;
  55     uint64_t off, end;
  56
  57     if (flags & BDRV_REQ_WRITE_UNCHANGED) {
  58         return 0;
  59     }
  60
  61     off = QEMU_ALIGN_DOWN(offset, s->cluster_size);
  62     end = QEMU_ALIGN_UP(offset + bytes, s->cluster_size);
  63
  64     return block_copy(s->bcs, off, end - off, NULL);
  65 }
  66
  67 static int coroutine_fn backup_top_co_pdiscard(BlockDriverState *bs,
  68                                                int64_t offset, int bytes)
  69 {
  70     int ret = backup_top_cbw(bs, offset, bytes, 0);
  71     if (ret < 0) {
  72         return ret;
  73     }
  74
  75     return bdrv_co_pdiscard(bs->backing, offset, bytes);
  76 }
  77
  78 static int coroutine_fn backup_top_co_pwrite_zeroes(BlockDriverState *bs,
  79         int64_t offset, int bytes, BdrvRequestFlags flags)
  80 {
  81     int ret = backup_top_cbw(bs, offset, bytes, flags);
  82     if (ret < 0) {
  83         return ret;
  84     }
  85
  86     return bdrv_co_pwrite_zeroes(bs->backing, offset, bytes, flags);
  87 }
  88
  89 static coroutine_fn int backup_top_co_pwritev(BlockDriverState *bs,
  90                                               uint64_t offset,
  91                                               uint64_t bytes,
  92                                               QEMUIOVector *qiov, int flags)
  93 {
  94     int ret = backup_top_cbw(bs, offset, bytes, flags);
  95     if (ret < 0) {
  96         return ret;
  97     }
  98
  99     return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
 100 }
 101
 102 static int coroutine_fn backup_top_co_flush(BlockDriverState *bs)
 103 {
 104     if (!bs->backing) {
 105         return 0;
 106     }
 107
 108     return bdrv_co_flush(bs->backing->bs);
 109 }
 110
 111 static void backup_top_refresh_filename(BlockDriverState *bs)
 112 {
 113     if (bs->backing == NULL) {
 114         /*
 115          * we can be here after failed bdrv_attach_child in
 116          * bdrv_set_backing_hd
 117          */
 118         return;
 119     }
 120     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
 121             bs->backing->bs->filename);
 122 }
 123
 124 static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
 125                                   const BdrvChildRole *role,
 126                                   BlockReopenQueue *reopen_queue,
 127                                   uint64_t perm, uint64_t shared,
 128                                   uint64_t *nperm, uint64_t *nshared)
 129 {
 130     BDRVBackupTopState *s = bs->opaque;
 131
 132     if (!s->active) {
 133         /*
 134          * The filter node may be in process of bdrv_append(), which firstly do
 135          * bdrv_set_backing_hd() and then bdrv_replace_node(). This means that
 136          * we can't unshare BLK_PERM_WRITE during bdrv_append() operation. So,
 137          * let's require nothing during bdrv_append() and refresh permissions
 138          * after it (see bdrv_backup_top_append()).
 139          */
 140         *nperm = 0;
 141         *nshared = BLK_PERM_ALL;
 142         return;
 143     }
 144
 145     if (role == &child_file) {
 146         /*
 147          * Target child
 148          *
 149          * Share write to target (child_file), to not interfere
 150          * with guest writes to its disk which may be in target backing chain.
 151          */
 152         *nshared = BLK_PERM_ALL;
 153         *nperm = BLK_PERM_WRITE;
 154     } else {
 155         /* Source child */
 156         bdrv_filter_default_perms(bs, c, role, reopen_queue, perm, shared,
 157                                   nperm, nshared);
 158
 159         if (perm & BLK_PERM_WRITE) {
 160             *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
 161         }
 162         *nshared &= ~BLK_PERM_WRITE;
 163     }
 164 }
 165
 166 BlockDriver bdrv_backup_top_filter = {
 167     .format_name = "backup-top",
 168     .instance_size = sizeof(BDRVBackupTopState),
 169
 170     .bdrv_co_preadv             = backup_top_co_preadv,
 171     .bdrv_co_pwritev            = backup_top_co_pwritev,
 172     .bdrv_co_pwrite_zeroes      = backup_top_co_pwrite_zeroes,
 173     .bdrv_co_pdiscard           = backup_top_co_pdiscard,
 174     .bdrv_co_flush              = backup_top_co_flush,
 175
 176     .bdrv_co_block_status       = bdrv_co_block_status_from_backing,
 177
 178     .bdrv_refresh_filename      = backup_top_refresh_filename,
 179
 180     .bdrv_child_perm            = backup_top_child_perm,
 181
 182     .is_filter = true,
 183 };
 184
 185 BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
 186                                          BlockDriverState *target,
 187                                          const char *filter_node_name,
 188                                          uint64_t cluster_size,
 189                                          BdrvRequestFlags write_flags,
 190                                          BlockCopyState **bcs,
 191                                          Error **errp)
 192 {
 193     Error *local_err = NULL;
 194     BDRVBackupTopState *state;
 195     BlockDriverState *top = bdrv_new_open_driver(&bdrv_backup_top_filter,
 196                                                  filter_node_name,
 197                                                  BDRV_O_RDWR, errp);
 198     bool appended = false;
 199
 200     if (!top) {
 201         return NULL;
 202     }
 203
 204     state = top->opaque;
 205     top->total_sectors = source->total_sectors;
 206     top->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
 207             (BDRV_REQ_FUA & source->supported_write_flags);
 208     top->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
 209             ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
 210              source->supported_zero_flags);
 211
 212     bdrv_ref(target);
 213     state->target = bdrv_attach_child(top, target, "target", &child_file, errp);
 214     if (!state->target) {
 215         bdrv_unref(target);
 216         bdrv_unref(top);
 217         return NULL;
 218     }
 219
 220     bdrv_drained_begin(source);
 221
 222     bdrv_ref(top);
 223     bdrv_append(top, source, &local_err);
 224     if (local_err) {
 225         error_prepend(&local_err, "Cannot append backup-top filter: ");
 226         goto fail;
 227     }
 228     appended = true;
 229
 230     /*
 231      * bdrv_append() finished successfully, now we can require permissions
 232      * we want.
 233      */
 234     state->active = true;
 235     bdrv_child_refresh_perms(top, top->backing, &local_err);
 236     if (local_err) {
 237         error_prepend(&local_err,
 238                       "Cannot set permissions for backup-top filter: ");
 239         goto fail;
 240     }
 241
 242     state->cluster_size = cluster_size;
 243     state->bcs = block_copy_state_new(top->backing, state->target,
 244                                       cluster_size, write_flags, &local_err);
 245     if (local_err) {
 246         error_prepend(&local_err, "Cannot create block-copy-state: ");
 247         goto fail;
 248     }
 249     *bcs = state->bcs;
 250
 251     bdrv_drained_end(source);
 252
 253     return top;
 254
 255 fail:
 256     if (appended) {
 257         state->active = false;
 258         bdrv_backup_top_drop(top);
 259     } else {
 260         bdrv_unref(top);
 261     }
 262
 263     bdrv_drained_end(source);
 264     error_propagate(errp, local_err);
 265
 266     return NULL;
 267 }
 268
 269 void bdrv_backup_top_drop(BlockDriverState *bs)
 270 {
 271     BDRVBackupTopState *s = bs->opaque;
 272
 273     bdrv_drained_begin(bs);
 274
 275     block_copy_state_free(s->bcs);
 276
 277     s->active = false;
 278     bdrv_child_refresh_perms(bs, bs->backing, &error_abort);
 279     bdrv_replace_node(bs, backing_bs(bs), &error_abort);
 280     bdrv_set_backing_hd(bs, NULL, &error_abort);
 281
 282     bdrv_drained_end(bs);
 283
 284     bdrv_unref(bs);
 285 }