block/copy-on-read.c

   1 /*
   2  * Copy-on-read filter block driver
   3  *
   4  * Copyright (c) 2018 Red Hat, Inc.
   5  *
   6  * Author:
   7  *   Max Reitz <mreitz@redhat.com>
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License as
  11  * published by the Free Software Foundation; either version 2 or
  12  * (at your option) version 3 of the License.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  21  */
  22
  23 #include "qemu/osdep.h"
  24 #include "block/block_int.h"
  25 #include "qemu/module.h"
  26 #include "qapi/error.h"
  27 #include "qapi/qmp/qdict.h"
  28 #include "block/copy-on-read.h"
  29
  30
  31 typedef struct BDRVStateCOR {
  32     BlockDriverState *bottom_bs;
  33     bool chain_frozen;
  34 } BDRVStateCOR;
  35
  36
  37 static int cor_open(BlockDriverState *bs, QDict *options, int flags,
  38                     Error **errp)
  39 {
  40     BlockDriverState *bottom_bs = NULL;
  41     BDRVStateCOR *state = bs->opaque;
  42     /* Find a bottom node name, if any */
  43     const char *bottom_node = qdict_get_try_str(options, "bottom");
  44     int ret;
  45
  46     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
  47     if (ret < 0) {
  48         return ret;
  49     }
  50
  51     bs->supported_read_flags = BDRV_REQ_PREFETCH;
  52
  53     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
  54         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
  55
  56     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
  57         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
  58             bs->file->bs->supported_zero_flags);
  59
  60     if (bottom_node) {
  61         bottom_bs = bdrv_find_node(bottom_node);
  62         if (!bottom_bs) {
  63             error_setg(errp, "Bottom node '%s' not found", bottom_node);
  64             qdict_del(options, "bottom");
  65             return -EINVAL;
  66         }
  67         qdict_del(options, "bottom");
  68
  69         if (!bottom_bs->drv) {
  70             error_setg(errp, "Bottom node '%s' not opened", bottom_node);
  71             return -EINVAL;
  72         }
  73
  74         if (bottom_bs->drv->is_filter) {
  75             error_setg(errp, "Bottom node '%s' is a filter", bottom_node);
  76             return -EINVAL;
  77         }
  78
  79         if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) {
  80             return -EINVAL;
  81         }
  82         state->chain_frozen = true;
  83
  84         /*
  85          * We do freeze the chain, so it shouldn't be removed. Still, storing a
  86          * pointer worth bdrv_ref().
  87          */
  88         bdrv_ref(bottom_bs);
  89     }
  90     state->bottom_bs = bottom_bs;
  91
  92     /*
  93      * We don't need to call bdrv_child_refresh_perms() now as the permissions
  94      * will be updated later when the filter node gets its parent.
  95      */
  96
  97     return 0;
  98 }
  99
 100
 101 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
 102                           | BLK_PERM_WRITE \
 103                           | BLK_PERM_RESIZE)
 104 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
 105
 106 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
 107                            BdrvChildRole role,
 108                            BlockReopenQueue *reopen_queue,
 109                            uint64_t perm, uint64_t shared,
 110                            uint64_t *nperm, uint64_t *nshared)
 111 {
 112     *nperm = perm & PERM_PASSTHROUGH;
 113     *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
 114
 115     /* We must not request write permissions for an inactive node, the child
 116      * cannot provide it. */
 117     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
 118         *nperm |= BLK_PERM_WRITE_UNCHANGED;
 119     }
 120 }
 121
 122
 123 static int64_t cor_getlength(BlockDriverState *bs)
 124 {
 125     return bdrv_getlength(bs->file->bs);
 126 }
 127
 128
 129 static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
 130                                            int64_t offset, int64_t bytes,
 131                                            QEMUIOVector *qiov,
 132                                            size_t qiov_offset,
 133                                            BdrvRequestFlags flags)
 134 {
 135     int64_t n;
 136     int local_flags;
 137     int ret;
 138     BDRVStateCOR *state = bs->opaque;
 139
 140     if (!state->bottom_bs) {
 141         return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
 142                                    flags | BDRV_REQ_COPY_ON_READ);
 143     }
 144
 145     while (bytes) {
 146         local_flags = flags;
 147
 148         /* In case of failure, try to copy-on-read anyway */
 149         ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
 150         if (ret <= 0) {
 151             ret = bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
 152                                           state->bottom_bs, true, offset,
 153                                           n, &n);
 154             if (ret > 0 || ret < 0) {
 155                 local_flags |= BDRV_REQ_COPY_ON_READ;
 156             }
 157             /* Finish earlier if the end of a backing file has been reached */
 158             if (n == 0) {
 159                 break;
 160             }
 161         }
 162
 163         /* Skip if neither read nor write are needed */
 164         if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=
 165             BDRV_REQ_PREFETCH) {
 166             ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
 167                                       local_flags);
 168             if (ret < 0) {
 169                 return ret;
 170             }
 171         }
 172
 173         offset += n;
 174         qiov_offset += n;
 175         bytes -= n;
 176     }
 177
 178     return 0;
 179 }
 180
 181
 182 static int coroutine_fn cor_co_pwritev_part(BlockDriverState *bs,
 183                                             int64_t offset,
 184                                             int64_t bytes,
 185                                             QEMUIOVector *qiov,
 186                                             size_t qiov_offset,
 187                                             BdrvRequestFlags flags)
 188 {
 189     return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
 190                                 flags);
 191 }
 192
 193
 194 static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
 195                                              int64_t offset, int64_t bytes,
 196                                              BdrvRequestFlags flags)
 197 {
 198     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 199 }
 200
 201
 202 static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
 203                                         int64_t offset, int64_t bytes)
 204 {
 205     return bdrv_co_pdiscard(bs->file, offset, bytes);
 206 }
 207
 208
 209 static int coroutine_fn cor_co_pwritev_compressed(BlockDriverState *bs,
 210                                                   int64_t offset,
 211                                                   int64_t bytes,
 212                                                   QEMUIOVector *qiov)
 213 {
 214     return bdrv_co_pwritev(bs->file, offset, bytes, qiov,
 215                            BDRV_REQ_WRITE_COMPRESSED);
 216 }
 217
 218
 219 static void cor_eject(BlockDriverState *bs, bool eject_flag)
 220 {
 221     bdrv_eject(bs->file->bs, eject_flag);
 222 }
 223
 224
 225 static void cor_lock_medium(BlockDriverState *bs, bool locked)
 226 {
 227     bdrv_lock_medium(bs->file->bs, locked);
 228 }
 229
 230
 231 static void cor_close(BlockDriverState *bs)
 232 {
 233     BDRVStateCOR *s = bs->opaque;
 234
 235     if (s->chain_frozen) {
 236         s->chain_frozen = false;
 237         bdrv_unfreeze_backing_chain(bs, s->bottom_bs);
 238     }
 239
 240     bdrv_unref(s->bottom_bs);
 241 }
 242
 243
 244 static BlockDriver bdrv_copy_on_read = {
 245     .format_name                        = "copy-on-read",
 246     .instance_size                      = sizeof(BDRVStateCOR),
 247
 248     .bdrv_open                          = cor_open,
 249     .bdrv_close                         = cor_close,
 250     .bdrv_child_perm                    = cor_child_perm,
 251
 252     .bdrv_getlength                     = cor_getlength,
 253
 254     .bdrv_co_preadv_part                = cor_co_preadv_part,
 255     .bdrv_co_pwritev_part               = cor_co_pwritev_part,
 256     .bdrv_co_pwrite_zeroes              = cor_co_pwrite_zeroes,
 257     .bdrv_co_pdiscard                   = cor_co_pdiscard,
 258     .bdrv_co_pwritev_compressed         = cor_co_pwritev_compressed,
 259
 260     .bdrv_eject                         = cor_eject,
 261     .bdrv_lock_medium                   = cor_lock_medium,
 262
 263     .has_variable_length                = true,
 264     .is_filter                          = true,
 265 };
 266
 267
 268 void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
 269 {
 270     BDRVStateCOR *s = cor_filter_bs->opaque;
 271
 272     /* unfreeze, as otherwise bdrv_replace_node() will fail */
 273     if (s->chain_frozen) {
 274         s->chain_frozen = false;
 275         bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs);
 276     }
 277     bdrv_drop_filter(cor_filter_bs, &error_abort);
 278     bdrv_unref(cor_filter_bs);
 279 }
 280
 281
 282 static void bdrv_copy_on_read_init(void)
 283 {
 284     bdrv_register(&bdrv_copy_on_read);
 285 }
 286
 287 block_init(bdrv_copy_on_read_init);