xref: /qemu/block/export/export.c (revision 78f314cf) 
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 #ifdef CONFIG_VDUSE_BLK_EXPORT
30 #include "vduse-blk.h"
31 #endif
32 
33 static const BlockExportDriver *blk_exp_drivers[] = {
34     &blk_exp_nbd,
35 #ifdef CONFIG_VHOST_USER_BLK_SERVER
36     &blk_exp_vhost_user_blk,
37 #endif
38 #ifdef CONFIG_FUSE
39     &blk_exp_fuse,
40 #endif
41 #ifdef CONFIG_VDUSE_BLK_EXPORT
42     &blk_exp_vduse_blk,
43 #endif
44 };
45 
46 /* Only accessed from the main thread */
47 static QLIST_HEAD(, BlockExport) block_exports =
48     QLIST_HEAD_INITIALIZER(block_exports);
49 
50 BlockExport *blk_exp_find(const char *id)
51 {
52     BlockExport *exp;
53 
54     QLIST_FOREACH(exp, &block_exports, next) {
55         if (strcmp(id, exp->id) == 0) {
56             return exp;
57         }
58     }
59 
60     return NULL;
61 }
62 
63 static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
64 {
65     int i;
66 
67     for (i = 0; i < ARRAY_SIZE(blk_exp_drivers); i++) {
68         if (blk_exp_drivers[i]->type == type) {
69             return blk_exp_drivers[i];
70         }
71     }
72     return NULL;
73 }
74 
75 BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
76 {
77     bool fixed_iothread = export->has_fixed_iothread && export->fixed_iothread;
78     const BlockExportDriver *drv;
79     BlockExport *exp = NULL;
80     BlockDriverState *bs;
81     BlockBackend *blk = NULL;
82     AioContext *ctx;
83     uint64_t perm;
84     int ret;
85 
86     if (!id_wellformed(export->id)) {
87         error_setg(errp, "Invalid block export id");
88         return NULL;
89     }
90     if (blk_exp_find(export->id)) {
91         error_setg(errp, "Block export id '%s' is already in use", export->id);
92         return NULL;
93     }
94 
95     drv = blk_exp_find_driver(export->type);
96     if (!drv) {
97         error_setg(errp, "No driver found for the requested export type");
98         return NULL;
99     }
100 
101     bs = bdrv_lookup_bs(NULL, export->node_name, errp);
102     if (!bs) {
103         return NULL;
104     }
105 
106     if (!export->has_writable) {
107         export->writable = false;
108     }
109     if (bdrv_is_read_only(bs) && export->writable) {
110         error_setg(errp, "Cannot export read-only node as writable");
111         return NULL;
112     }
113 
114     ctx = bdrv_get_aio_context(bs);
115     aio_context_acquire(ctx);
116 
117     if (export->iothread) {
118         IOThread *iothread;
119         AioContext *new_ctx;
120         Error **set_context_errp;
121 
122         iothread = iothread_by_id(export->iothread);
123         if (!iothread) {
124             error_setg(errp, "iothread \"%s\" not found", export->iothread);
125             goto fail;
126         }
127 
128         new_ctx = iothread_get_aio_context(iothread);
129 
130         /* Ignore errors with fixed-iothread=false */
131         set_context_errp = fixed_iothread ? errp : NULL;
132         ret = bdrv_try_change_aio_context(bs, new_ctx, NULL, set_context_errp);
133         if (ret == 0) {
134             aio_context_release(ctx);
135             aio_context_acquire(new_ctx);
136             ctx = new_ctx;
137         } else if (fixed_iothread) {
138             goto fail;
139         }
140     }
141 
142     /*
143      * Block exports are used for non-shared storage migration. Make sure
144      * that BDRV_O_INACTIVE is cleared and the image is ready for write
145      * access since the export could be available before migration handover.
146      * ctx was acquired in the caller.
147      */
148     bdrv_activate(bs, NULL);
149 
150     perm = BLK_PERM_CONSISTENT_READ;
151     if (export->writable) {
152         perm |= BLK_PERM_WRITE;
153     }
154 
155     blk = blk_new(ctx, perm, BLK_PERM_ALL);
156 
157     if (!fixed_iothread) {
158         blk_set_allow_aio_context_change(blk, true);
159     }
160 
161     ret = blk_insert_bs(blk, bs, errp);
162     if (ret < 0) {
163         goto fail;
164     }
165 
166     if (!export->has_writethrough) {
167         export->writethrough = false;
168     }
169     blk_set_enable_write_cache(blk, !export->writethrough);
170 
171     assert(drv->instance_size >= sizeof(BlockExport));
172     exp = g_malloc0(drv->instance_size);
173     *exp = (BlockExport) {
174         .drv        = drv,
175         .refcount   = 1,
176         .user_owned = true,
177         .id         = g_strdup(export->id),
178         .ctx        = ctx,
179         .blk        = blk,
180     };
181 
182     ret = drv->create(exp, export, errp);
183     if (ret < 0) {
184         goto fail;
185     }
186 
187     assert(exp->blk != NULL);
188 
189     QLIST_INSERT_HEAD(&block_exports, exp, next);
190 
191     aio_context_release(ctx);
192     return exp;
193 
194 fail:
195     if (blk) {
196         blk_set_dev_ops(blk, NULL, NULL);
197         blk_unref(blk);
198     }
199     aio_context_release(ctx);
200     if (exp) {
201         g_free(exp->id);
202         g_free(exp);
203     }
204     return NULL;
205 }
206 
207 void blk_exp_ref(BlockExport *exp)
208 {
209     assert(qatomic_read(&exp->refcount) > 0);
210     qatomic_inc(&exp->refcount);
211 }
212 
213 /* Runs in the main thread */
214 static void blk_exp_delete_bh(void *opaque)
215 {
216     BlockExport *exp = opaque;
217     AioContext *aio_context = exp->ctx;
218 
219     aio_context_acquire(aio_context);
220 
221     assert(exp->refcount == 0);
222     QLIST_REMOVE(exp, next);
223     exp->drv->delete(exp);
224     blk_set_dev_ops(exp->blk, NULL, NULL);
225     blk_unref(exp->blk);
226     qapi_event_send_block_export_deleted(exp->id);
227     g_free(exp->id);
228     g_free(exp);
229 
230     aio_context_release(aio_context);
231 }
232 
233 void blk_exp_unref(BlockExport *exp)
234 {
235     assert(qatomic_read(&exp->refcount) > 0);
236     if (qatomic_fetch_dec(&exp->refcount) == 1) {
237         /* Touch the block_exports list only in the main thread */
238         aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh,
239                                 exp);
240     }
241 }
242 
243 /*
244  * Drops the user reference to the export and requests that all client
245  * connections and other internally held references start to shut down. When
246  * the function returns, there may still be active references while the export
247  * is in the process of shutting down.
248  *
249  * Acquires exp->ctx internally. Callers must *not* hold the lock.
250  */
251 void blk_exp_request_shutdown(BlockExport *exp)
252 {
253     AioContext *aio_context = exp->ctx;
254 
255     aio_context_acquire(aio_context);
256 
257     /*
258      * If the user doesn't own the export any more, it is already shutting
259      * down. We must not call .request_shutdown and decrease the refcount a
260      * second time.
261      */
262     if (!exp->user_owned) {
263         goto out;
264     }
265 
266     exp->drv->request_shutdown(exp);
267 
268     assert(exp->user_owned);
269     exp->user_owned = false;
270     blk_exp_unref(exp);
271 
272 out:
273     aio_context_release(aio_context);
274 }
275 
276 /*
277  * Returns whether a block export of the given type exists.
278  * type == BLOCK_EXPORT_TYPE__MAX checks for an export of any type.
279  */
280 static bool blk_exp_has_type(BlockExportType type)
281 {
282     BlockExport *exp;
283 
284     if (type == BLOCK_EXPORT_TYPE__MAX) {
285         return !QLIST_EMPTY(&block_exports);
286     }
287 
288     QLIST_FOREACH(exp, &block_exports, next) {
289         if (exp->drv->type == type) {
290             return true;
291         }
292     }
293 
294     return false;
295 }
296 
297 /* type == BLOCK_EXPORT_TYPE__MAX for all types */
298 void blk_exp_close_all_type(BlockExportType type)
299 {
300     BlockExport *exp, *next;
301 
302     assert(in_aio_context_home_thread(qemu_get_aio_context()));
303 
304     QLIST_FOREACH_SAFE(exp, &block_exports, next, next) {
305         if (type != BLOCK_EXPORT_TYPE__MAX && exp->drv->type != type) {
306             continue;
307         }
308         blk_exp_request_shutdown(exp);
309     }
310 
311     AIO_WAIT_WHILE_UNLOCKED(NULL, blk_exp_has_type(type));
312 }
313 
314 void blk_exp_close_all(void)
315 {
316     blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX);
317 }
318 
319 void qmp_block_export_add(BlockExportOptions *export, Error **errp)
320 {
321     blk_exp_add(export, errp);
322 }
323 
324 void qmp_block_export_del(const char *id,
325                           bool has_mode, BlockExportRemoveMode mode,
326                           Error **errp)
327 {
328     ERRP_GUARD();
329     BlockExport *exp;
330 
331     exp = blk_exp_find(id);
332     if (exp == NULL) {
333         error_setg(errp, "Export '%s' is not found", id);
334         return;
335     }
336     if (!exp->user_owned) {
337         error_setg(errp, "Export '%s' is already shutting down", id);
338         return;
339     }
340 
341     if (!has_mode) {
342         mode = BLOCK_EXPORT_REMOVE_MODE_SAFE;
343     }
344     if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE &&
345         qatomic_read(&exp->refcount) > 1) {
346         error_setg(errp, "export '%s' still in use", exp->id);
347         error_append_hint(errp, "Use mode='hard' to force client "
348                           "disconnect\n");
349         return;
350     }
351 
352     blk_exp_request_shutdown(exp);
353 }
354 
355 BlockExportInfoList *qmp_query_block_exports(Error **errp)
356 {
357     BlockExportInfoList *head = NULL, **tail = &head;
358     BlockExport *exp;
359 
360     QLIST_FOREACH(exp, &block_exports, next) {
361         BlockExportInfo *info = g_new(BlockExportInfo, 1);
362         *info = (BlockExportInfo) {
363             .id             = g_strdup(exp->id),
364             .type           = exp->drv->type,
365             .node_name      = g_strdup(bdrv_get_node_name(blk_bs(exp->blk))),
366             .shutting_down  = !exp->user_owned,
367         };
368 
369         QAPI_LIST_APPEND(tail, info);
370     }
371 
372     return head;
373 }
374