copy-on-read.c (8821B)
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);