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                                   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 & BDRV_CHILD_FILTERED)) {
 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          * Can't resize during a backup block job because we check the size
 152          * only upfront.
 153          */
 154         *nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
 155         *nperm = BLK_PERM_WRITE;
 156     } else {
 157         /* Source child */
 158         bdrv_default_perms(bs, c, role, reopen_queue,
 159                            perm, shared, nperm, nshared);
 160
 161         if (perm & BLK_PERM_WRITE) {
 162             *nperm = *nperm | BLK_PERM_CONSISTENT_READ;
 163         }
 164         *nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
 165     }
 166 }
 167
 168 BlockDriver bdrv_backup_top_filter = {
 169     .format_name = "backup-top",
 170     .instance_size = sizeof(BDRVBackupTopState),
 171
 172     .bdrv_co_preadv             = backup_top_co_preadv,
 173     .bdrv_co_pwritev            = backup_top_co_pwritev,
 174     .bdrv_co_pwrite_zeroes      = backup_top_co_pwrite_zeroes,
 175     .bdrv_co_pdiscard           = backup_top_co_pdiscard,
 176     .bdrv_co_flush              = backup_top_co_flush,
 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;
 196     bool appended = false;
 197
 198     assert(source->total_sectors == target->total_sectors);
 199
 200     top = bdrv_new_open_driver(&bdrv_backup_top_filter, filter_node_name,
 201                                BDRV_O_RDWR, errp);
 202     if (!top) {
 203         return NULL;
 204     }
 205
 206     state = top->opaque;
 207     top->total_sectors = source->total_sectors;
 208     top->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
 209             (BDRV_REQ_FUA & source->supported_write_flags);
 210     top->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
 211             ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
 212              source->supported_zero_flags);
 213
 214     bdrv_ref(target);
 215     state->target = bdrv_attach_child(top, target, "target", &child_of_bds,
 216                                       BDRV_CHILD_DATA, errp);
 217     if (!state->target) {
 218         bdrv_unref(target);
 219         bdrv_unref(top);
 220         return NULL;
 221     }
 222
 223     bdrv_drained_begin(source);
 224
 225     bdrv_ref(top);
 226     bdrv_append(top, source, &local_err);
 227     if (local_err) {
 228         error_prepend(&local_err, "Cannot append backup-top filter: ");
 229         goto fail;
 230     }
 231     appended = true;
 232
 233     /*
 234      * bdrv_append() finished successfully, now we can require permissions
 235      * we want.
 236      */
 237     state->active = true;
 238     bdrv_child_refresh_perms(top, top->backing, &local_err);
 239     if (local_err) {
 240         error_prepend(&local_err,
 241                       "Cannot set permissions for backup-top filter: ");
 242         goto fail;
 243     }
 244
 245     state->cluster_size = cluster_size;
 246     state->bcs = block_copy_state_new(top->backing, state->target,
 247                                       cluster_size, write_flags, &local_err);
 248     if (local_err) {
 249         error_prepend(&local_err, "Cannot create block-copy-state: ");
 250         goto fail;
 251     }
 252     *bcs = state->bcs;
 253
 254     bdrv_drained_end(source);
 255
 256     return top;
 257
 258 fail:
 259     if (appended) {
 260         state->active = false;
 261         bdrv_backup_top_drop(top);
 262     } else {
 263         bdrv_unref(top);
 264     }
 265
 266     bdrv_drained_end(source);
 267     error_propagate(errp, local_err);
 268
 269     return NULL;
 270 }
 271
 272 void bdrv_backup_top_drop(BlockDriverState *bs)
 273 {
 274     BDRVBackupTopState *s = bs->opaque;
 275
 276     bdrv_drained_begin(bs);
 277
 278     block_copy_state_free(s->bcs);
 279
 280     s->active = false;
 281     bdrv_child_refresh_perms(bs, bs->backing, &error_abort);
 282     bdrv_replace_node(bs, bs->backing->bs, &error_abort);
 283     bdrv_set_backing_hd(bs, NULL, &error_abort);
 284
 285     bdrv_drained_end(bs);
 286
 287     bdrv_unref(bs);
 288 }