block/export/export.c

   1 /*
   2  * Common block export infrastructure
   3  *
   4  * Copyright (c) 2012, 2020 Red Hat, Inc.
   5  *
   6  * Authors:
   7  * Paolo Bonzini <pbonzini@redhat.com>
   8  * Kevin Wolf <kwolf@redhat.com>
   9  *
  10  * This work is licensed under the terms of the GNU GPL, version 2 or
  11  * later.  See the COPYING file in the top-level directory.
  12  */
  13
  14 #include "qemu/osdep.h"
  15
  16 #include "block/block.h"
  17 #include "sysemu/block-backend.h"
  18 #include "sysemu/iothread.h"
  19 #include "block/export.h"
  20 #include "block/fuse.h"
  21 #include "block/nbd.h"
  22 #include "qapi/error.h"
  23 #include "qapi/qapi-commands-block-export.h"
  24 #include "qapi/qapi-events-block-export.h"
  25 #include "qemu/id.h"
  26 #ifdef CONFIG_VHOST_USER_BLK_SERVER
  27 #include "vhost-user-blk-server.h"
  28 #endif
  29
  30 static const BlockExportDriver *blk_exp_drivers[] = {
  31     &blk_exp_nbd,
  32 #ifdef CONFIG_VHOST_USER_BLK_SERVER
  33     &blk_exp_vhost_user_blk,
  34 #endif
  35 #ifdef CONFIG_FUSE
  36     &blk_exp_fuse,
  37 #endif
  38 };
  39
  40 /* Only accessed from the main thread */
  41 static QLIST_HEAD(, BlockExport) block_exports =
  42     QLIST_HEAD_INITIALIZER(block_exports);
  43
  44 BlockExport *blk_exp_find(const char *id)
  45 {
  46     BlockExport *exp;
  47
  48     QLIST_FOREACH(exp, &block_exports, next) {
  49         if (strcmp(id, exp->id) == 0) {
  50             return exp;
  51         }
  52     }
  53
  54     return NULL;
  55 }
  56
  57 static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
  58 {
  59     int i;
  60
  61     for (i = 0; i < ARRAY_SIZE(blk_exp_drivers); i++) {
  62         if (blk_exp_drivers[i]->type == type) {
  63             return blk_exp_drivers[i];
  64         }
  65     }
  66     return NULL;
  67 }
  68
  69 BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
  70 {
  71     bool fixed_iothread = export->has_fixed_iothread && export->fixed_iothread;
  72     const BlockExportDriver *drv;
  73     BlockExport *exp = NULL;
  74     BlockDriverState *bs;
  75     BlockBackend *blk = NULL;
  76     AioContext *ctx;
  77     uint64_t perm;
  78     int ret;
  79
  80     if (!id_wellformed(export->id)) {
  81         error_setg(errp, "Invalid block export id");
  82         return NULL;
  83     }
  84     if (blk_exp_find(export->id)) {
  85         error_setg(errp, "Block export id '%s' is already in use", export->id);
  86         return NULL;
  87     }
  88
  89     drv = blk_exp_find_driver(export->type);
  90     if (!drv) {
  91         error_setg(errp, "No driver found for the requested export type");
  92         return NULL;
  93     }
  94
  95     bs = bdrv_lookup_bs(NULL, export->node_name, errp);
  96     if (!bs) {
  97         return NULL;
  98     }
  99
 100     if (!export->has_writable) {
 101         export->writable = false;
 102     }
 103     if (bdrv_is_read_only(bs) && export->writable) {
 104         error_setg(errp, "Cannot export read-only node as writable");
 105         return NULL;
 106     }
 107
 108     ctx = bdrv_get_aio_context(bs);
 109     aio_context_acquire(ctx);
 110
 111     if (export->has_iothread) {
 112         IOThread *iothread;
 113         AioContext *new_ctx;
 114
 115         iothread = iothread_by_id(export->iothread);
 116         if (!iothread) {
 117             error_setg(errp, "iothread \"%s\" not found", export->iothread);
 118             goto fail;
 119         }
 120
 121         new_ctx = iothread_get_aio_context(iothread);
 122
 123         ret = bdrv_try_set_aio_context(bs, new_ctx, errp);
 124         if (ret == 0) {
 125             aio_context_release(ctx);
 126             aio_context_acquire(new_ctx);
 127             ctx = new_ctx;
 128         } else if (fixed_iothread) {
 129             goto fail;
 130         }
 131     }
 132
 133     /*
 134      * Block exports are used for non-shared storage migration. Make sure
 135      * that BDRV_O_INACTIVE is cleared and the image is ready for write
 136      * access since the export could be available before migration handover.
 137      * ctx was acquired in the caller.
 138      */
 139     bdrv_invalidate_cache(bs, NULL);
 140
 141     perm = BLK_PERM_CONSISTENT_READ;
 142     if (export->writable) {
 143         perm |= BLK_PERM_WRITE;
 144     }
 145
 146     blk = blk_new(ctx, perm, BLK_PERM_ALL);
 147
 148     if (!fixed_iothread) {
 149         blk_set_allow_aio_context_change(blk, true);
 150     }
 151
 152     ret = blk_insert_bs(blk, bs, errp);
 153     if (ret < 0) {
 154         goto fail;
 155     }
 156
 157     if (!export->has_writethrough) {
 158         export->writethrough = false;
 159     }
 160     blk_set_enable_write_cache(blk, !export->writethrough);
 161
 162     assert(drv->instance_size >= sizeof(BlockExport));
 163     exp = g_malloc0(drv->instance_size);
 164     *exp = (BlockExport) {
 165         .drv        = drv,
 166         .refcount   = 1,
 167         .user_owned = true,
 168         .id         = g_strdup(export->id),
 169         .ctx        = ctx,
 170         .blk        = blk,
 171     };
 172
 173     ret = drv->create(exp, export, errp);
 174     if (ret < 0) {
 175         goto fail;
 176     }
 177
 178     assert(exp->blk != NULL);
 179
 180     QLIST_INSERT_HEAD(&block_exports, exp, next);
 181
 182     aio_context_release(ctx);
 183     return exp;
 184
 185 fail:
 186     blk_unref(blk);
 187     aio_context_release(ctx);
 188     if (exp) {
 189         g_free(exp->id);
 190         g_free(exp);
 191     }
 192     return NULL;
 193 }
 194
 195 /* Callers must hold exp->ctx lock */
 196 void blk_exp_ref(BlockExport *exp)
 197 {
 198     assert(exp->refcount > 0);
 199     exp->refcount++;
 200 }
 201
 202 /* Runs in the main thread */
 203 static void blk_exp_delete_bh(void *opaque)
 204 {
 205     BlockExport *exp = opaque;
 206     AioContext *aio_context = exp->ctx;
 207
 208     aio_context_acquire(aio_context);
 209
 210     assert(exp->refcount == 0);
 211     QLIST_REMOVE(exp, next);
 212     exp->drv->delete(exp);
 213     blk_unref(exp->blk);
 214     qapi_event_send_block_export_deleted(exp->id);
 215     g_free(exp->id);
 216     g_free(exp);
 217
 218     aio_context_release(aio_context);
 219 }
 220
 221 /* Callers must hold exp->ctx lock */
 222 void blk_exp_unref(BlockExport *exp)
 223 {
 224     assert(exp->refcount > 0);
 225     if (--exp->refcount == 0) {
 226         /* Touch the block_exports list only in the main thread */
 227         aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh,
 228                                 exp);
 229     }
 230 }
 231
 232 /*
 233  * Drops the user reference to the export and requests that all client
 234  * connections and other internally held references start to shut down. When
 235  * the function returns, there may still be active references while the export
 236  * is in the process of shutting down.
 237  *
 238  * Acquires exp->ctx internally. Callers must *not* hold the lock.
 239  */
 240 void blk_exp_request_shutdown(BlockExport *exp)
 241 {
 242     AioContext *aio_context = exp->ctx;
 243
 244     aio_context_acquire(aio_context);
 245
 246     /*
 247      * If the user doesn't own the export any more, it is already shutting
 248      * down. We must not call .request_shutdown and decrease the refcount a
 249      * second time.
 250      */
 251     if (!exp->user_owned) {
 252         goto out;
 253     }
 254
 255     exp->drv->request_shutdown(exp);
 256
 257     assert(exp->user_owned);
 258     exp->user_owned = false;
 259     blk_exp_unref(exp);
 260
 261 out:
 262     aio_context_release(aio_context);
 263 }
 264
 265 /*
 266  * Returns whether a block export of the given type exists.
 267  * type == BLOCK_EXPORT_TYPE__MAX checks for an export of any type.
 268  */
 269 static bool blk_exp_has_type(BlockExportType type)
 270 {
 271     BlockExport *exp;
 272
 273     if (type == BLOCK_EXPORT_TYPE__MAX) {
 274         return !QLIST_EMPTY(&block_exports);
 275     }
 276
 277     QLIST_FOREACH(exp, &block_exports, next) {
 278         if (exp->drv->type == type) {
 279             return true;
 280         }
 281     }
 282
 283     return false;
 284 }
 285
 286 /* type == BLOCK_EXPORT_TYPE__MAX for all types */
 287 void blk_exp_close_all_type(BlockExportType type)
 288 {
 289     BlockExport *exp, *next;
 290
 291     assert(in_aio_context_home_thread(qemu_get_aio_context()));
 292
 293     QLIST_FOREACH_SAFE(exp, &block_exports, next, next) {
 294         if (type != BLOCK_EXPORT_TYPE__MAX && exp->drv->type != type) {
 295             continue;
 296         }
 297         blk_exp_request_shutdown(exp);
 298     }
 299
 300     AIO_WAIT_WHILE(NULL, blk_exp_has_type(type));
 301 }
 302
 303 void blk_exp_close_all(void)
 304 {
 305     blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX);
 306 }
 307
 308 void qmp_block_export_add(BlockExportOptions *export, Error **errp)
 309 {
 310     blk_exp_add(export, errp);
 311 }
 312
 313 void qmp_block_export_del(const char *id,
 314                           bool has_mode, BlockExportRemoveMode mode,
 315                           Error **errp)
 316 {
 317     ERRP_GUARD();
 318     BlockExport *exp;
 319
 320     exp = blk_exp_find(id);
 321     if (exp == NULL) {
 322         error_setg(errp, "Export '%s' is not found", id);
 323         return;
 324     }
 325     if (!exp->user_owned) {
 326         error_setg(errp, "Export '%s' is already shutting down", id);
 327         return;
 328     }
 329
 330     if (!has_mode) {
 331         mode = BLOCK_EXPORT_REMOVE_MODE_SAFE;
 332     }
 333     if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE && exp->refcount > 1) {
 334         error_setg(errp, "export '%s' still in use", exp->id);
 335         error_append_hint(errp, "Use mode='hard' to force client "
 336                           "disconnect\n");
 337         return;
 338     }
 339
 340     blk_exp_request_shutdown(exp);
 341 }
 342
 343 BlockExportInfoList *qmp_query_block_exports(Error **errp)
 344 {
 345     BlockExportInfoList *head = NULL, **p_next = &head;
 346     BlockExport *exp;
 347
 348     QLIST_FOREACH(exp, &block_exports, next) {
 349         BlockExportInfoList *entry = g_new0(BlockExportInfoList, 1);
 350         BlockExportInfo *info = g_new(BlockExportInfo, 1);
 351         *info = (BlockExportInfo) {
 352             .id             = g_strdup(exp->id),
 353             .type           = exp->drv->type,
 354             .node_name      = g_strdup(bdrv_get_node_name(blk_bs(exp->blk))),
 355             .shutting_down  = !exp->user_owned,
 356         };
 357
 358         entry->value = info;
 359         *p_next = entry;
 360         p_next = &entry->next;
 361     }
 362
 363     return head;
 364 }