xref: /openbmc/qemu/block/stream.c (revision 72098a3a)
1 /*
2  * Image streaming
3  *
4  * Copyright IBM, Corp. 2011
5  *
6  * Authors:
7  *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
8  *
9  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
10  * See the COPYING.LIB file in the top-level directory.
11  *
12  */
13 
14 #include "qemu/osdep.h"
15 #include "trace.h"
16 #include "block/block_int.h"
17 #include "block/blockjob_int.h"
18 #include "qapi/error.h"
19 #include "qapi/qmp/qdict.h"
20 #include "qemu/ratelimit.h"
21 #include "sysemu/block-backend.h"
22 #include "block/copy-on-read.h"
23 
24 enum {
25     /*
26      * Maximum chunk size to feed to copy-on-read.  This should be
27      * large enough to process multiple clusters in a single call, so
28      * that populating contiguous regions of the image is efficient.
29      */
30     STREAM_CHUNK = 512 * 1024, /* in bytes */
31 };
32 
33 typedef struct StreamBlockJob {
34     BlockJob common;
35     BlockBackend *blk;
36     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
37     BlockDriverState *above_base;   /* Node directly above the base */
38     BlockDriverState *cor_filter_bs;
39     BlockDriverState *target_bs;
40     BlockdevOnError on_error;
41     char *backing_file_str;
42     bool backing_mask_protocol;
43     bool bs_read_only;
44 } StreamBlockJob;
45 
stream_populate(BlockBackend * blk,int64_t offset,uint64_t bytes)46 static int coroutine_fn stream_populate(BlockBackend *blk,
47                                         int64_t offset, uint64_t bytes)
48 {
49     assert(bytes < SIZE_MAX);
50 
51     return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
52 }
53 
stream_prepare(Job * job)54 static int stream_prepare(Job *job)
55 {
56     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
57     BlockDriverState *unfiltered_bs;
58     BlockDriverState *unfiltered_bs_cow;
59     BlockDriverState *base;
60     BlockDriverState *unfiltered_base;
61     Error *local_err = NULL;
62     int ret = 0;
63 
64     GLOBAL_STATE_CODE();
65 
66     bdrv_graph_rdlock_main_loop();
67     unfiltered_bs = bdrv_skip_filters(s->target_bs);
68     unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
69     bdrv_graph_rdunlock_main_loop();
70 
71     /* We should drop filter at this point, as filter hold the backing chain */
72     bdrv_cor_filter_drop(s->cor_filter_bs);
73     s->cor_filter_bs = NULL;
74 
75     /*
76      * bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
77      * of unfiltered_bs is drained. Drain already here and use
78      * bdrv_set_backing_hd_drained() instead because the polling during
79      * drained_begin() might change the graph, and if we do this only later, we
80      * may end up working with the wrong base node (or it might even have gone
81      * away by the time we want to use it).
82      */
83     bdrv_drained_begin(unfiltered_bs);
84     if (unfiltered_bs_cow) {
85         bdrv_ref(unfiltered_bs_cow);
86         bdrv_drained_begin(unfiltered_bs_cow);
87     }
88 
89     bdrv_graph_rdlock_main_loop();
90     base = bdrv_filter_or_cow_bs(s->above_base);
91     unfiltered_base = bdrv_skip_filters(base);
92     bdrv_graph_rdunlock_main_loop();
93 
94     if (unfiltered_bs_cow) {
95         const char *base_id = NULL, *base_fmt = NULL;
96         if (unfiltered_base) {
97             base_id = s->backing_file_str ?: unfiltered_base->filename;
98             if (unfiltered_base->drv) {
99                 if (s->backing_mask_protocol &&
100                     unfiltered_base->drv->protocol_name) {
101                     base_fmt = "raw";
102                 } else {
103                     base_fmt = unfiltered_base->drv->format_name;
104                 }
105             }
106         }
107 
108         bdrv_graph_wrlock();
109         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
110         bdrv_graph_wrunlock();
111 
112         /*
113          * This call will do I/O, so the graph can change again from here on.
114          * We have already completed the graph change, so we are not in danger
115          * of operating on the wrong node any more if this happens.
116          */
117         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
118         if (local_err) {
119             error_report_err(local_err);
120             ret = -EPERM;
121             goto out;
122         }
123     }
124 
125 out:
126     if (unfiltered_bs_cow) {
127         bdrv_drained_end(unfiltered_bs_cow);
128         bdrv_unref(unfiltered_bs_cow);
129     }
130     bdrv_drained_end(unfiltered_bs);
131     return ret;
132 }
133 
stream_clean(Job * job)134 static void stream_clean(Job *job)
135 {
136     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
137 
138     if (s->cor_filter_bs) {
139         bdrv_cor_filter_drop(s->cor_filter_bs);
140         s->cor_filter_bs = NULL;
141     }
142 
143     blk_unref(s->blk);
144     s->blk = NULL;
145 
146     /* Reopen the image back in read-only mode if necessary */
147     if (s->bs_read_only) {
148         /* Give up write permissions before making it read-only */
149         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
150     }
151 
152     g_free(s->backing_file_str);
153 }
154 
stream_run(Job * job,Error ** errp)155 static int coroutine_fn stream_run(Job *job, Error **errp)
156 {
157     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
158     BlockDriverState *unfiltered_bs;
159     int64_t len;
160     int64_t offset = 0;
161     int error = 0;
162     int64_t n = 0; /* bytes */
163 
164     WITH_GRAPH_RDLOCK_GUARD() {
165         unfiltered_bs = bdrv_skip_filters(s->target_bs);
166         if (unfiltered_bs == s->base_overlay) {
167             /* Nothing to stream */
168             return 0;
169         }
170 
171         len = bdrv_co_getlength(s->target_bs);
172         if (len < 0) {
173             return len;
174         }
175     }
176     job_progress_set_remaining(&s->common.job, len);
177 
178     for ( ; offset < len; offset += n) {
179         bool copy;
180         int ret;
181 
182         /* Note that even when no rate limit is applied we need to yield
183          * with no pending I/O here so that bdrv_drain_all() returns.
184          */
185         block_job_ratelimit_sleep(&s->common);
186         if (job_is_cancelled(&s->common.job)) {
187             break;
188         }
189 
190         copy = false;
191 
192         WITH_GRAPH_RDLOCK_GUARD() {
193             ret = bdrv_co_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
194             if (ret == 1) {
195                 /* Allocated in the top, no need to copy.  */
196             } else if (ret >= 0) {
197                 /*
198                  * Copy if allocated in the intermediate images.  Limit to the
199                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
200                  */
201                 ret = bdrv_co_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
202                                                  s->base_overlay, true,
203                                                  offset, n, &n);
204                 /* Finish early if end of backing file has been reached */
205                 if (ret == 0 && n == 0) {
206                     n = len - offset;
207                 }
208 
209                 copy = (ret > 0);
210             }
211         }
212         trace_stream_one_iteration(s, offset, n, ret);
213         if (copy) {
214             ret = stream_populate(s->blk, offset, n);
215         }
216         if (ret < 0) {
217             BlockErrorAction action =
218                 block_job_error_action(&s->common, s->on_error, true, -ret);
219             if (action == BLOCK_ERROR_ACTION_STOP) {
220                 n = 0;
221                 continue;
222             }
223             if (error == 0) {
224                 error = ret;
225             }
226             if (action == BLOCK_ERROR_ACTION_REPORT) {
227                 break;
228             }
229         }
230 
231         /* Publish progress */
232         job_progress_update(&s->common.job, n);
233         if (copy) {
234             block_job_ratelimit_processed_bytes(&s->common, n);
235         }
236     }
237 
238     /* Do not remove the backing file if an error was there but ignored. */
239     return error;
240 }
241 
242 static const BlockJobDriver stream_job_driver = {
243     .job_driver = {
244         .instance_size = sizeof(StreamBlockJob),
245         .job_type      = JOB_TYPE_STREAM,
246         .free          = block_job_free,
247         .run           = stream_run,
248         .prepare       = stream_prepare,
249         .clean         = stream_clean,
250         .user_resume   = block_job_user_resume,
251     },
252 };
253 
stream_start(const char * job_id,BlockDriverState * bs,BlockDriverState * base,const char * backing_file_str,bool backing_mask_protocol,BlockDriverState * bottom,int creation_flags,int64_t speed,BlockdevOnError on_error,const char * filter_node_name,Error ** errp)254 void stream_start(const char *job_id, BlockDriverState *bs,
255                   BlockDriverState *base, const char *backing_file_str,
256                   bool backing_mask_protocol,
257                   BlockDriverState *bottom,
258                   int creation_flags, int64_t speed,
259                   BlockdevOnError on_error,
260                   const char *filter_node_name,
261                   Error **errp)
262 {
263     StreamBlockJob *s = NULL;
264     BlockDriverState *iter;
265     bool bs_read_only;
266     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
267     BlockDriverState *base_overlay;
268     BlockDriverState *cor_filter_bs = NULL;
269     BlockDriverState *above_base;
270     QDict *opts;
271     int ret;
272 
273     GLOBAL_STATE_CODE();
274 
275     assert(!(base && bottom));
276     assert(!(backing_file_str && bottom));
277 
278     bdrv_graph_rdlock_main_loop();
279 
280     if (bottom) {
281         /*
282          * New simple interface. The code is written in terms of old interface
283          * with @base parameter (still, it doesn't freeze link to base, so in
284          * this mean old code is correct for new interface). So, for now, just
285          * emulate base_overlay and above_base. Still, when old interface
286          * finally removed, we should refactor code to use only "bottom", but
287          * not "*base*" things.
288          */
289         assert(!bottom->drv->is_filter);
290         base_overlay = above_base = bottom;
291     } else {
292         base_overlay = bdrv_find_overlay(bs, base);
293         if (!base_overlay) {
294             error_setg(errp, "'%s' is not in the backing chain of '%s'",
295                        base->node_name, bs->node_name);
296             goto out_rdlock;
297         }
298 
299         /*
300          * Find the node directly above @base.  @base_overlay is a COW overlay,
301          * so it must have a bdrv_cow_child(), but it is the immediate overlay
302          * of @base, so between the two there can only be filters.
303          */
304         above_base = base_overlay;
305         if (bdrv_cow_bs(above_base) != base) {
306             above_base = bdrv_cow_bs(above_base);
307             while (bdrv_filter_bs(above_base) != base) {
308                 above_base = bdrv_filter_bs(above_base);
309             }
310         }
311     }
312 
313     /* Make sure that the image is opened in read-write mode */
314     bs_read_only = bdrv_is_read_only(bs);
315     if (bs_read_only) {
316         /* Hold the chain during reopen */
317         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
318             goto out_rdlock;
319         }
320 
321         ret = bdrv_reopen_set_read_only(bs, false, errp);
322 
323         /* failure, or cor-filter will hold the chain */
324         bdrv_unfreeze_backing_chain(bs, above_base);
325 
326         if (ret < 0) {
327             goto out_rdlock;
328         }
329     }
330 
331     bdrv_graph_rdunlock_main_loop();
332 
333     opts = qdict_new();
334 
335     qdict_put_str(opts, "driver", "copy-on-read");
336     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
337     /* Pass the base_overlay node name as 'bottom' to COR driver */
338     qdict_put_str(opts, "bottom", base_overlay->node_name);
339     if (filter_node_name) {
340         qdict_put_str(opts, "node-name", filter_node_name);
341     }
342 
343     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
344     if (!cor_filter_bs) {
345         goto fail;
346     }
347 
348     if (!filter_node_name) {
349         cor_filter_bs->implicit = true;
350     }
351 
352     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
353                          0, BLK_PERM_ALL,
354                          speed, creation_flags, NULL, NULL, errp);
355     if (!s) {
356         goto fail;
357     }
358 
359     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
360                              basic_flags | BLK_PERM_WRITE, errp);
361     if (!s->blk) {
362         goto fail;
363     }
364     /*
365      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
366      * The job reports that it's busy until it reaches a pause point.
367      */
368     blk_set_disable_request_queuing(s->blk, true);
369     blk_set_allow_aio_context_change(s->blk, true);
370 
371     /*
372      * Prevent concurrent jobs trying to modify the graph structure here, we
373      * already have our own plans. Also don't allow resize as the image size is
374      * queried only at the job start and then cached.
375      */
376     bdrv_graph_wrlock();
377     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
378                            basic_flags | BLK_PERM_WRITE, errp)) {
379         bdrv_graph_wrunlock();
380         goto fail;
381     }
382 
383     /* Block all intermediate nodes between bs and base, because they will
384      * disappear from the chain after this operation. The streaming job reads
385      * every block only once, assuming that it doesn't change, so forbid writes
386      * and resizes. Reassign the base node pointer because the backing BS of the
387      * bottom node might change after the call to bdrv_reopen_set_read_only()
388      * due to parallel block jobs running.
389      * above_base node might change after the call to
390      * bdrv_reopen_set_read_only() due to parallel block jobs running.
391      */
392     base = bdrv_filter_or_cow_bs(above_base);
393     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
394          iter = bdrv_filter_or_cow_bs(iter))
395     {
396         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
397                                  basic_flags, errp);
398         if (ret < 0) {
399             bdrv_graph_wrunlock();
400             goto fail;
401         }
402     }
403     bdrv_graph_wrunlock();
404 
405     s->base_overlay = base_overlay;
406     s->above_base = above_base;
407     s->backing_file_str = g_strdup(backing_file_str);
408     s->backing_mask_protocol = backing_mask_protocol;
409     s->cor_filter_bs = cor_filter_bs;
410     s->target_bs = bs;
411     s->bs_read_only = bs_read_only;
412 
413     s->on_error = on_error;
414     trace_stream_start(bs, base, s);
415     job_start(&s->common.job);
416     return;
417 
418 fail:
419     if (s) {
420         job_early_fail(&s->common.job);
421     }
422     if (cor_filter_bs) {
423         bdrv_cor_filter_drop(cor_filter_bs);
424     }
425     if (bs_read_only) {
426         bdrv_reopen_set_read_only(bs, true, NULL);
427     }
428     return;
429 
430 out_rdlock:
431     bdrv_graph_rdunlock_main_loop();
432 }
433