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-io.h"
  25 #include "block/block_int.h"
  26 #include "qemu/module.h"
  27 #include "qapi/error.h"
  28 #include "qapi/qmp/qdict.h"
  29 #include "block/copy-on-read.h"
  30
  31
  32 typedef struct BDRVStateCOR {
  33     BlockDriverState *bottom_bs;
  34     bool chain_frozen;
  35 } BDRVStateCOR;
  36
  37
  38 static int GRAPH_UNLOCKED
  39 cor_open(BlockDriverState *bs, QDict *options, int flags, Error **errp)
  40 {
  41     BlockDriverState *bottom_bs = NULL;
  42     BDRVStateCOR *state = bs->opaque;
  43     /* Find a bottom node name, if any */
  44     const char *bottom_node = qdict_get_try_str(options, "bottom");
  45     int ret;
  46
  47     GLOBAL_STATE_CODE();
  48
  49     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
  50     if (ret < 0) {
  51         return ret;
  52     }
  53
  54     bs->supported_read_flags = BDRV_REQ_PREFETCH;
  55
  56     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
  57         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
  58
  59     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
  60         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
  61             bs->file->bs->supported_zero_flags);
  62
  63     if (bottom_node) {
  64         GRAPH_RDLOCK_GUARD_MAINLOOP();
  65
  66         bottom_bs = bdrv_find_node(bottom_node);
  67         if (!bottom_bs) {
  68             error_setg(errp, "Bottom node '%s' not found", bottom_node);
  69             qdict_del(options, "bottom");
  70             return -EINVAL;
  71         }
  72         qdict_del(options, "bottom");
  73
  74         if (!bottom_bs->drv) {
  75             error_setg(errp, "Bottom node '%s' not opened", bottom_node);
  76             return -EINVAL;
  77         }
  78
  79         if (bottom_bs->drv->is_filter) {
  80             error_setg(errp, "Bottom node '%s' is a filter", bottom_node);
  81             return -EINVAL;
  82         }
  83
  84         if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) {
  85             return -EINVAL;
  86         }
  87         state->chain_frozen = true;
  88
  89         /*
  90          * We do freeze the chain, so it shouldn't be removed. Still, storing a
  91          * pointer worth bdrv_ref().
  92          */
  93         bdrv_ref(bottom_bs);
  94     }
  95     state->bottom_bs = bottom_bs;
  96
  97     /*
  98      * We don't need to call bdrv_child_refresh_perms() now as the permissions
  99      * will be updated later when the filter node gets its parent.
 100      */
 101
 102     return 0;
 103 }
 104
 105
 106 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
 107                           | BLK_PERM_WRITE \
 108                           | BLK_PERM_RESIZE)
 109 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
 110
 111 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
 112                            BdrvChildRole role,
 113                            BlockReopenQueue *reopen_queue,
 114                            uint64_t perm, uint64_t shared,
 115                            uint64_t *nperm, uint64_t *nshared)
 116 {
 117     *nperm = perm & PERM_PASSTHROUGH;
 118     *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
 119
 120     /* We must not request write permissions for an inactive node, the child
 121      * cannot provide it. */
 122     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
 123         *nperm |= BLK_PERM_WRITE_UNCHANGED;
 124     }
 125 }
 126
 127
 128 static int64_t coroutine_fn GRAPH_RDLOCK cor_co_getlength(BlockDriverState *bs)
 129 {
 130     return bdrv_co_getlength(bs->file->bs);
 131 }
 132
 133
 134 static int coroutine_fn GRAPH_RDLOCK
 135 cor_co_preadv_part(BlockDriverState *bs, int64_t offset, int64_t bytes,
 136                    QEMUIOVector *qiov, size_t qiov_offset,
 137                    BdrvRequestFlags flags)
 138 {
 139     int64_t n;
 140     int local_flags;
 141     int ret;
 142     BDRVStateCOR *state = bs->opaque;
 143
 144     if (!state->bottom_bs) {
 145         return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
 146                                    flags | BDRV_REQ_COPY_ON_READ);
 147     }
 148
 149     while (bytes) {
 150         local_flags = flags;
 151
 152         /* In case of failure, try to copy-on-read anyway */
 153         ret = bdrv_co_is_allocated(bs->file->bs, offset, bytes, &n);
 154         if (ret <= 0) {
 155             ret = bdrv_co_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
 156                                              state->bottom_bs, true, offset,
 157                                              n, &n);
 158             if (ret > 0 || ret < 0) {
 159                 local_flags |= BDRV_REQ_COPY_ON_READ;
 160             }
 161             /* Finish earlier if the end of a backing file has been reached */
 162             if (n == 0) {
 163                 break;
 164             }
 165         }
 166
 167         /* Skip if neither read nor write are needed */
 168         if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=
 169             BDRV_REQ_PREFETCH) {
 170             ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
 171                                       local_flags);
 172             if (ret < 0) {
 173                 return ret;
 174             }
 175         }
 176
 177         offset += n;
 178         qiov_offset += n;
 179         bytes -= n;
 180     }
 181
 182     return 0;
 183 }
 184
 185
 186 static int coroutine_fn GRAPH_RDLOCK
 187 cor_co_pwritev_part(BlockDriverState *bs, int64_t offset, int64_t bytes,
 188                     QEMUIOVector *qiov, size_t qiov_offset,
 189                     BdrvRequestFlags flags)
 190 {
 191     return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
 192                                 flags);
 193 }
 194
 195
 196 static int coroutine_fn GRAPH_RDLOCK
 197 cor_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
 198                      BdrvRequestFlags flags)
 199 {
 200     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 201 }
 202
 203
 204 static int coroutine_fn GRAPH_RDLOCK
 205 cor_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 206 {
 207     return bdrv_co_pdiscard(bs->file, offset, bytes);
 208 }
 209
 210
 211 static int coroutine_fn GRAPH_RDLOCK
 212 cor_co_pwritev_compressed(BlockDriverState *bs, int64_t offset, int64_t bytes,
 213                           QEMUIOVector *qiov)
 214 {
 215     return bdrv_co_pwritev(bs->file, offset, bytes, qiov,
 216                            BDRV_REQ_WRITE_COMPRESSED);
 217 }
 218
 219
 220 static void coroutine_fn GRAPH_RDLOCK
 221 cor_co_eject(BlockDriverState *bs, bool eject_flag)
 222 {
 223     bdrv_co_eject(bs->file->bs, eject_flag);
 224 }
 225
 226
 227 static void coroutine_fn GRAPH_RDLOCK
 228 cor_co_lock_medium(BlockDriverState *bs, bool locked)
 229 {
 230     bdrv_co_lock_medium(bs->file->bs, locked);
 231 }
 232
 233
 234 static void GRAPH_UNLOCKED cor_close(BlockDriverState *bs)
 235 {
 236     BDRVStateCOR *s = bs->opaque;
 237
 238     GLOBAL_STATE_CODE();
 239
 240     if (s->chain_frozen) {
 241         bdrv_graph_rdlock_main_loop();
 242         s->chain_frozen = false;
 243         bdrv_unfreeze_backing_chain(bs, s->bottom_bs);
 244         bdrv_graph_rdunlock_main_loop();
 245     }
 246
 247     bdrv_unref(s->bottom_bs);
 248 }
 249
 250
 251 static BlockDriver bdrv_copy_on_read = {
 252     .format_name                        = "copy-on-read",
 253     .instance_size                      = sizeof(BDRVStateCOR),
 254
 255     .bdrv_open                          = cor_open,
 256     .bdrv_close                         = cor_close,
 257     .bdrv_child_perm                    = cor_child_perm,
 258
 259     .bdrv_co_getlength                  = cor_co_getlength,
 260
 261     .bdrv_co_preadv_part                = cor_co_preadv_part,
 262     .bdrv_co_pwritev_part               = cor_co_pwritev_part,
 263     .bdrv_co_pwrite_zeroes              = cor_co_pwrite_zeroes,
 264     .bdrv_co_pdiscard                   = cor_co_pdiscard,
 265     .bdrv_co_pwritev_compressed         = cor_co_pwritev_compressed,
 266
 267     .bdrv_co_eject                      = cor_co_eject,
 268     .bdrv_co_lock_medium                = cor_co_lock_medium,
 269
 270     .is_filter                          = true,
 271 };
 272
 273
 274 void no_coroutine_fn bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
 275 {
 276     BDRVStateCOR *s = cor_filter_bs->opaque;
 277
 278     GLOBAL_STATE_CODE();
 279
 280     /* unfreeze, as otherwise bdrv_replace_node() will fail */
 281     if (s->chain_frozen) {
 282         GRAPH_RDLOCK_GUARD_MAINLOOP();
 283         s->chain_frozen = false;
 284         bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs);
 285     }
 286     bdrv_drop_filter(cor_filter_bs, &error_abort);
 287     bdrv_unref(cor_filter_bs);
 288 }
 289
 290
 291 static void bdrv_copy_on_read_init(void)
 292 {
 293     bdrv_register(&bdrv_copy_on_read);
 294 }
 295
 296 block_init(bdrv_copy_on_read_init);