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 cor_open(BlockDriverState *bs, QDict *options, int flags, 39 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 ret = bdrv_open_file_child(NULL, options, "file", bs, errp); 48 if (ret < 0) { 49 return ret; 50 } 51 52 bs->supported_read_flags = BDRV_REQ_PREFETCH; 53 54 bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED | 55 (BDRV_REQ_FUA & bs->file->bs->supported_write_flags); 56 57 bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED | 58 ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) & 59 bs->file->bs->supported_zero_flags); 60 61 if (bottom_node) { 62 bottom_bs = bdrv_find_node(bottom_node); 63 if (!bottom_bs) { 64 error_setg(errp, "Bottom node '%s' not found", bottom_node); 65 qdict_del(options, "bottom"); 66 return -EINVAL; 67 } 68 qdict_del(options, "bottom"); 69 70 if (!bottom_bs->drv) { 71 error_setg(errp, "Bottom node '%s' not opened", bottom_node); 72 return -EINVAL; 73 } 74 75 if (bottom_bs->drv->is_filter) { 76 error_setg(errp, "Bottom node '%s' is a filter", bottom_node); 77 return -EINVAL; 78 } 79 80 if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) { 81 return -EINVAL; 82 } 83 state->chain_frozen = true; 84 85 /* 86 * We do freeze the chain, so it shouldn't be removed. Still, storing a 87 * pointer worth bdrv_ref(). 88 */ 89 bdrv_ref(bottom_bs); 90 } 91 state->bottom_bs = bottom_bs; 92 93 /* 94 * We don't need to call bdrv_child_refresh_perms() now as the permissions 95 * will be updated later when the filter node gets its parent. 96 */ 97 98 return 0; 99 } 100 101 102 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \ 103 | BLK_PERM_WRITE \ 104 | BLK_PERM_RESIZE) 105 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH) 106 107 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c, 108 BdrvChildRole role, 109 BlockReopenQueue *reopen_queue, 110 uint64_t perm, uint64_t shared, 111 uint64_t *nperm, uint64_t *nshared) 112 { 113 *nperm = perm & PERM_PASSTHROUGH; 114 *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED; 115 116 /* We must not request write permissions for an inactive node, the child 117 * cannot provide it. */ 118 if (!(bs->open_flags & BDRV_O_INACTIVE)) { 119 *nperm |= BLK_PERM_WRITE_UNCHANGED; 120 } 121 } 122 123 124 static int64_t coroutine_fn GRAPH_RDLOCK cor_co_getlength(BlockDriverState *bs) 125 { 126 return bdrv_co_getlength(bs->file->bs); 127 } 128 129 130 static int coroutine_fn GRAPH_RDLOCK 131 cor_co_preadv_part(BlockDriverState *bs, int64_t offset, int64_t bytes, 132 QEMUIOVector *qiov, 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 GRAPH_RDLOCK 183 cor_co_pwritev_part(BlockDriverState *bs, int64_t offset, int64_t bytes, 184 QEMUIOVector *qiov, size_t qiov_offset, 185 BdrvRequestFlags flags) 186 { 187 return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset, 188 flags); 189 } 190 191 192 static int coroutine_fn GRAPH_RDLOCK 193 cor_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes, 194 BdrvRequestFlags flags) 195 { 196 return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags); 197 } 198 199 200 static int coroutine_fn GRAPH_RDLOCK 201 cor_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes) 202 { 203 return bdrv_co_pdiscard(bs->file, offset, bytes); 204 } 205 206 207 static int coroutine_fn GRAPH_RDLOCK 208 cor_co_pwritev_compressed(BlockDriverState *bs, int64_t offset, int64_t bytes, 209 QEMUIOVector *qiov) 210 { 211 return bdrv_co_pwritev(bs->file, offset, bytes, qiov, 212 BDRV_REQ_WRITE_COMPRESSED); 213 } 214 215 216 static void coroutine_fn GRAPH_RDLOCK 217 cor_co_eject(BlockDriverState *bs, bool eject_flag) 218 { 219 bdrv_co_eject(bs->file->bs, eject_flag); 220 } 221 222 223 static void coroutine_fn GRAPH_RDLOCK 224 cor_co_lock_medium(BlockDriverState *bs, bool locked) 225 { 226 bdrv_co_lock_medium(bs->file->bs, locked); 227 } 228 229 230 static void cor_close(BlockDriverState *bs) 231 { 232 BDRVStateCOR *s = bs->opaque; 233 234 if (s->chain_frozen) { 235 s->chain_frozen = false; 236 bdrv_unfreeze_backing_chain(bs, s->bottom_bs); 237 } 238 239 bdrv_unref(s->bottom_bs); 240 } 241 242 243 static BlockDriver bdrv_copy_on_read = { 244 .format_name = "copy-on-read", 245 .instance_size = sizeof(BDRVStateCOR), 246 247 .bdrv_open = cor_open, 248 .bdrv_close = cor_close, 249 .bdrv_child_perm = cor_child_perm, 250 251 .bdrv_co_getlength = cor_co_getlength, 252 253 .bdrv_co_preadv_part = cor_co_preadv_part, 254 .bdrv_co_pwritev_part = cor_co_pwritev_part, 255 .bdrv_co_pwrite_zeroes = cor_co_pwrite_zeroes, 256 .bdrv_co_pdiscard = cor_co_pdiscard, 257 .bdrv_co_pwritev_compressed = cor_co_pwritev_compressed, 258 259 .bdrv_co_eject = cor_co_eject, 260 .bdrv_co_lock_medium = cor_co_lock_medium, 261 262 .has_variable_length = true, 263 .is_filter = true, 264 }; 265 266 267 void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs) 268 { 269 BDRVStateCOR *s = cor_filter_bs->opaque; 270 271 /* unfreeze, as otherwise bdrv_replace_node() will fail */ 272 if (s->chain_frozen) { 273 s->chain_frozen = false; 274 bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs); 275 } 276 bdrv_drop_filter(cor_filter_bs, &error_abort); 277 bdrv_unref(cor_filter_bs); 278 } 279 280 281 static void bdrv_copy_on_read_init(void) 282 { 283 bdrv_register(&bdrv_copy_on_read); 284 } 285 286 block_init(bdrv_copy_on_read_init); 287