qapi2texi: Fix up output around #optional
[qemu.git] / migration / postcopy-ram.c
1 /*
2 * Postcopy migration for RAM
3 *
4 * Copyright 2013-2015 Red Hat, Inc. and/or its affiliates
5 *
6 * Authors:
7 * Dave Gilbert <dgilbert@redhat.com>
8 *
9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
10 * See the COPYING file in the top-level directory.
11 *
12 */
13
14 /*
15 * Postcopy is a migration technique where the execution flips from the
16 * source to the destination before all the data has been copied.
17 */
18
19 #include "qemu/osdep.h"
20
21 #include "qemu-common.h"
22 #include "migration/migration.h"
23 #include "migration/postcopy-ram.h"
24 #include "sysemu/sysemu.h"
25 #include "sysemu/balloon.h"
26 #include "qemu/error-report.h"
27 #include "trace.h"
28
29 /* Arbitrary limit on size of each discard command,
30 * keeps them around ~200 bytes
31 */
32 #define MAX_DISCARDS_PER_COMMAND 12
33
34 struct PostcopyDiscardState {
35 const char *ramblock_name;
36 uint64_t offset; /* Bitmap entry for the 1st bit of this RAMBlock */
37 uint16_t cur_entry;
38 /*
39 * Start and length of a discard range (bytes)
40 */
41 uint64_t start_list[MAX_DISCARDS_PER_COMMAND];
42 uint64_t length_list[MAX_DISCARDS_PER_COMMAND];
43 unsigned int nsentwords;
44 unsigned int nsentcmds;
45 };
46
47 /* Postcopy needs to detect accesses to pages that haven't yet been copied
48 * across, and efficiently map new pages in, the techniques for doing this
49 * are target OS specific.
50 */
51 #if defined(__linux__)
52
53 #include <poll.h>
54 #include <sys/ioctl.h>
55 #include <sys/syscall.h>
56 #include <asm/types.h> /* for __u64 */
57 #endif
58
59 #if defined(__linux__) && defined(__NR_userfaultfd) && defined(CONFIG_EVENTFD)
60 #include <sys/eventfd.h>
61 #include <linux/userfaultfd.h>
62
63 static bool ufd_version_check(int ufd)
64 {
65 struct uffdio_api api_struct;
66 uint64_t ioctl_mask;
67
68 api_struct.api = UFFD_API;
69 api_struct.features = 0;
70 if (ioctl(ufd, UFFDIO_API, &api_struct)) {
71 error_report("postcopy_ram_supported_by_host: UFFDIO_API failed: %s",
72 strerror(errno));
73 return false;
74 }
75
76 ioctl_mask = (__u64)1 << _UFFDIO_REGISTER |
77 (__u64)1 << _UFFDIO_UNREGISTER;
78 if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
79 error_report("Missing userfault features: %" PRIx64,
80 (uint64_t)(~api_struct.ioctls & ioctl_mask));
81 return false;
82 }
83
84 if (getpagesize() != ram_pagesize_summary()) {
85 bool have_hp = false;
86 /* We've got a huge page */
87 #ifdef UFFD_FEATURE_MISSING_HUGETLBFS
88 have_hp = api_struct.features & UFFD_FEATURE_MISSING_HUGETLBFS;
89 #endif
90 if (!have_hp) {
91 error_report("Userfault on this host does not support huge pages");
92 return false;
93 }
94 }
95 return true;
96 }
97
98 /*
99 * Note: This has the side effect of munlock'ing all of RAM, that's
100 * normally fine since if the postcopy succeeds it gets turned back on at the
101 * end.
102 */
103 bool postcopy_ram_supported_by_host(void)
104 {
105 long pagesize = getpagesize();
106 int ufd = -1;
107 bool ret = false; /* Error unless we change it */
108 void *testarea = NULL;
109 struct uffdio_register reg_struct;
110 struct uffdio_range range_struct;
111 uint64_t feature_mask;
112
113 if ((1ul << qemu_target_page_bits()) > pagesize) {
114 error_report("Target page size bigger than host page size");
115 goto out;
116 }
117
118 ufd = syscall(__NR_userfaultfd, O_CLOEXEC);
119 if (ufd == -1) {
120 error_report("%s: userfaultfd not available: %s", __func__,
121 strerror(errno));
122 goto out;
123 }
124
125 /* Version and features check */
126 if (!ufd_version_check(ufd)) {
127 goto out;
128 }
129
130 /*
131 * userfault and mlock don't go together; we'll put it back later if
132 * it was enabled.
133 */
134 if (munlockall()) {
135 error_report("%s: munlockall: %s", __func__, strerror(errno));
136 return -1;
137 }
138
139 /*
140 * We need to check that the ops we need are supported on anon memory
141 * To do that we need to register a chunk and see the flags that
142 * are returned.
143 */
144 testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE |
145 MAP_ANONYMOUS, -1, 0);
146 if (testarea == MAP_FAILED) {
147 error_report("%s: Failed to map test area: %s", __func__,
148 strerror(errno));
149 goto out;
150 }
151 g_assert(((size_t)testarea & (pagesize-1)) == 0);
152
153 reg_struct.range.start = (uintptr_t)testarea;
154 reg_struct.range.len = pagesize;
155 reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
156
157 if (ioctl(ufd, UFFDIO_REGISTER, &reg_struct)) {
158 error_report("%s userfault register: %s", __func__, strerror(errno));
159 goto out;
160 }
161
162 range_struct.start = (uintptr_t)testarea;
163 range_struct.len = pagesize;
164 if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
165 error_report("%s userfault unregister: %s", __func__, strerror(errno));
166 goto out;
167 }
168
169 feature_mask = (__u64)1 << _UFFDIO_WAKE |
170 (__u64)1 << _UFFDIO_COPY |
171 (__u64)1 << _UFFDIO_ZEROPAGE;
172 if ((reg_struct.ioctls & feature_mask) != feature_mask) {
173 error_report("Missing userfault map features: %" PRIx64,
174 (uint64_t)(~reg_struct.ioctls & feature_mask));
175 goto out;
176 }
177
178 /* Success! */
179 ret = true;
180 out:
181 if (testarea) {
182 munmap(testarea, pagesize);
183 }
184 if (ufd != -1) {
185 close(ufd);
186 }
187 return ret;
188 }
189
190 /*
191 * Setup an area of RAM so that it *can* be used for postcopy later; this
192 * must be done right at the start prior to pre-copy.
193 * opaque should be the MIS.
194 */
195 static int init_range(const char *block_name, void *host_addr,
196 ram_addr_t offset, ram_addr_t length, void *opaque)
197 {
198 MigrationIncomingState *mis = opaque;
199
200 trace_postcopy_init_range(block_name, host_addr, offset, length);
201
202 /*
203 * We need the whole of RAM to be truly empty for postcopy, so things
204 * like ROMs and any data tables built during init must be zero'd
205 * - we're going to get the copy from the source anyway.
206 * (Precopy will just overwrite this data, so doesn't need the discard)
207 */
208 if (ram_discard_range(mis, block_name, 0, length)) {
209 return -1;
210 }
211
212 return 0;
213 }
214
215 /*
216 * At the end of migration, undo the effects of init_range
217 * opaque should be the MIS.
218 */
219 static int cleanup_range(const char *block_name, void *host_addr,
220 ram_addr_t offset, ram_addr_t length, void *opaque)
221 {
222 MigrationIncomingState *mis = opaque;
223 struct uffdio_range range_struct;
224 trace_postcopy_cleanup_range(block_name, host_addr, offset, length);
225
226 /*
227 * We turned off hugepage for the precopy stage with postcopy enabled
228 * we can turn it back on now.
229 */
230 qemu_madvise(host_addr, length, QEMU_MADV_HUGEPAGE);
231
232 /*
233 * We can also turn off userfault now since we should have all the
234 * pages. It can be useful to leave it on to debug postcopy
235 * if you're not sure it's always getting every page.
236 */
237 range_struct.start = (uintptr_t)host_addr;
238 range_struct.len = length;
239
240 if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) {
241 error_report("%s: userfault unregister %s", __func__, strerror(errno));
242
243 return -1;
244 }
245
246 return 0;
247 }
248
249 /*
250 * Initialise postcopy-ram, setting the RAM to a state where we can go into
251 * postcopy later; must be called prior to any precopy.
252 * called from arch_init's similarly named ram_postcopy_incoming_init
253 */
254 int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
255 {
256 if (qemu_ram_foreach_block(init_range, mis)) {
257 return -1;
258 }
259
260 return 0;
261 }
262
263 /*
264 * At the end of a migration where postcopy_ram_incoming_init was called.
265 */
266 int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
267 {
268 trace_postcopy_ram_incoming_cleanup_entry();
269
270 if (mis->have_fault_thread) {
271 uint64_t tmp64;
272
273 if (qemu_ram_foreach_block(cleanup_range, mis)) {
274 return -1;
275 }
276 /*
277 * Tell the fault_thread to exit, it's an eventfd that should
278 * currently be at 0, we're going to increment it to 1
279 */
280 tmp64 = 1;
281 if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) {
282 trace_postcopy_ram_incoming_cleanup_join();
283 qemu_thread_join(&mis->fault_thread);
284 } else {
285 /* Not much we can do here, but may as well report it */
286 error_report("%s: incrementing userfault_quit_fd: %s", __func__,
287 strerror(errno));
288 }
289 trace_postcopy_ram_incoming_cleanup_closeuf();
290 close(mis->userfault_fd);
291 close(mis->userfault_quit_fd);
292 mis->have_fault_thread = false;
293 }
294
295 qemu_balloon_inhibit(false);
296
297 if (enable_mlock) {
298 if (os_mlock() < 0) {
299 error_report("mlock: %s", strerror(errno));
300 /*
301 * It doesn't feel right to fail at this point, we have a valid
302 * VM state.
303 */
304 }
305 }
306
307 postcopy_state_set(POSTCOPY_INCOMING_END);
308 migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0);
309
310 if (mis->postcopy_tmp_page) {
311 munmap(mis->postcopy_tmp_page, mis->largest_page_size);
312 mis->postcopy_tmp_page = NULL;
313 }
314 if (mis->postcopy_tmp_zero_page) {
315 munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size);
316 mis->postcopy_tmp_zero_page = NULL;
317 }
318 trace_postcopy_ram_incoming_cleanup_exit();
319 return 0;
320 }
321
322 /*
323 * Disable huge pages on an area
324 */
325 static int nhp_range(const char *block_name, void *host_addr,
326 ram_addr_t offset, ram_addr_t length, void *opaque)
327 {
328 trace_postcopy_nhp_range(block_name, host_addr, offset, length);
329
330 /*
331 * Before we do discards we need to ensure those discards really
332 * do delete areas of the page, even if THP thinks a hugepage would
333 * be a good idea, so force hugepages off.
334 */
335 qemu_madvise(host_addr, length, QEMU_MADV_NOHUGEPAGE);
336
337 return 0;
338 }
339
340 /*
341 * Userfault requires us to mark RAM as NOHUGEPAGE prior to discard
342 * however leaving it until after precopy means that most of the precopy
343 * data is still THPd
344 */
345 int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
346 {
347 if (qemu_ram_foreach_block(nhp_range, mis)) {
348 return -1;
349 }
350
351 postcopy_state_set(POSTCOPY_INCOMING_DISCARD);
352
353 return 0;
354 }
355
356 /*
357 * Mark the given area of RAM as requiring notification to unwritten areas
358 * Used as a callback on qemu_ram_foreach_block.
359 * host_addr: Base of area to mark
360 * offset: Offset in the whole ram arena
361 * length: Length of the section
362 * opaque: MigrationIncomingState pointer
363 * Returns 0 on success
364 */
365 static int ram_block_enable_notify(const char *block_name, void *host_addr,
366 ram_addr_t offset, ram_addr_t length,
367 void *opaque)
368 {
369 MigrationIncomingState *mis = opaque;
370 struct uffdio_register reg_struct;
371
372 reg_struct.range.start = (uintptr_t)host_addr;
373 reg_struct.range.len = length;
374 reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
375
376 /* Now tell our userfault_fd that it's responsible for this area */
377 if (ioctl(mis->userfault_fd, UFFDIO_REGISTER, &reg_struct)) {
378 error_report("%s userfault register: %s", __func__, strerror(errno));
379 return -1;
380 }
381 if (!(reg_struct.ioctls & ((__u64)1 << _UFFDIO_COPY))) {
382 error_report("%s userfault: Region doesn't support COPY", __func__);
383 return -1;
384 }
385
386 return 0;
387 }
388
389 /*
390 * Handle faults detected by the USERFAULT markings
391 */
392 static void *postcopy_ram_fault_thread(void *opaque)
393 {
394 MigrationIncomingState *mis = opaque;
395 struct uffd_msg msg;
396 int ret;
397 RAMBlock *rb = NULL;
398 RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */
399
400 trace_postcopy_ram_fault_thread_entry();
401 qemu_sem_post(&mis->fault_thread_sem);
402
403 while (true) {
404 ram_addr_t rb_offset;
405 struct pollfd pfd[2];
406
407 /*
408 * We're mainly waiting for the kernel to give us a faulting HVA,
409 * however we can be told to quit via userfault_quit_fd which is
410 * an eventfd
411 */
412 pfd[0].fd = mis->userfault_fd;
413 pfd[0].events = POLLIN;
414 pfd[0].revents = 0;
415 pfd[1].fd = mis->userfault_quit_fd;
416 pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */
417 pfd[1].revents = 0;
418
419 if (poll(pfd, 2, -1 /* Wait forever */) == -1) {
420 error_report("%s: userfault poll: %s", __func__, strerror(errno));
421 break;
422 }
423
424 if (pfd[1].revents) {
425 trace_postcopy_ram_fault_thread_quit();
426 break;
427 }
428
429 ret = read(mis->userfault_fd, &msg, sizeof(msg));
430 if (ret != sizeof(msg)) {
431 if (errno == EAGAIN) {
432 /*
433 * if a wake up happens on the other thread just after
434 * the poll, there is nothing to read.
435 */
436 continue;
437 }
438 if (ret < 0) {
439 error_report("%s: Failed to read full userfault message: %s",
440 __func__, strerror(errno));
441 break;
442 } else {
443 error_report("%s: Read %d bytes from userfaultfd expected %zd",
444 __func__, ret, sizeof(msg));
445 break; /* Lost alignment, don't know what we'd read next */
446 }
447 }
448 if (msg.event != UFFD_EVENT_PAGEFAULT) {
449 error_report("%s: Read unexpected event %ud from userfaultfd",
450 __func__, msg.event);
451 continue; /* It's not a page fault, shouldn't happen */
452 }
453
454 rb = qemu_ram_block_from_host(
455 (void *)(uintptr_t)msg.arg.pagefault.address,
456 true, &rb_offset);
457 if (!rb) {
458 error_report("postcopy_ram_fault_thread: Fault outside guest: %"
459 PRIx64, (uint64_t)msg.arg.pagefault.address);
460 break;
461 }
462
463 rb_offset &= ~(qemu_ram_pagesize(rb) - 1);
464 trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
465 qemu_ram_get_idstr(rb),
466 rb_offset);
467
468 /*
469 * Send the request to the source - we want to request one
470 * of our host page sizes (which is >= TPS)
471 */
472 if (rb != last_rb) {
473 last_rb = rb;
474 migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
475 rb_offset, qemu_ram_pagesize(rb));
476 } else {
477 /* Save some space */
478 migrate_send_rp_req_pages(mis, NULL,
479 rb_offset, qemu_ram_pagesize(rb));
480 }
481 }
482 trace_postcopy_ram_fault_thread_exit();
483 return NULL;
484 }
485
486 int postcopy_ram_enable_notify(MigrationIncomingState *mis)
487 {
488 /* Open the fd for the kernel to give us userfaults */
489 mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
490 if (mis->userfault_fd == -1) {
491 error_report("%s: Failed to open userfault fd: %s", __func__,
492 strerror(errno));
493 return -1;
494 }
495
496 /*
497 * Although the host check already tested the API, we need to
498 * do the check again as an ABI handshake on the new fd.
499 */
500 if (!ufd_version_check(mis->userfault_fd)) {
501 return -1;
502 }
503
504 /* Now an eventfd we use to tell the fault-thread to quit */
505 mis->userfault_quit_fd = eventfd(0, EFD_CLOEXEC);
506 if (mis->userfault_quit_fd == -1) {
507 error_report("%s: Opening userfault_quit_fd: %s", __func__,
508 strerror(errno));
509 close(mis->userfault_fd);
510 return -1;
511 }
512
513 qemu_sem_init(&mis->fault_thread_sem, 0);
514 qemu_thread_create(&mis->fault_thread, "postcopy/fault",
515 postcopy_ram_fault_thread, mis, QEMU_THREAD_JOINABLE);
516 qemu_sem_wait(&mis->fault_thread_sem);
517 qemu_sem_destroy(&mis->fault_thread_sem);
518 mis->have_fault_thread = true;
519
520 /* Mark so that we get notified of accesses to unwritten areas */
521 if (qemu_ram_foreach_block(ram_block_enable_notify, mis)) {
522 return -1;
523 }
524
525 /*
526 * Ballooning can mark pages as absent while we're postcopying
527 * that would cause false userfaults.
528 */
529 qemu_balloon_inhibit(true);
530
531 trace_postcopy_ram_enable_notify();
532
533 return 0;
534 }
535
536 /*
537 * Place a host page (from) at (host) atomically
538 * returns 0 on success
539 */
540 int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
541 size_t pagesize)
542 {
543 struct uffdio_copy copy_struct;
544
545 copy_struct.dst = (uint64_t)(uintptr_t)host;
546 copy_struct.src = (uint64_t)(uintptr_t)from;
547 copy_struct.len = pagesize;
548 copy_struct.mode = 0;
549
550 /* copy also acks to the kernel waking the stalled thread up
551 * TODO: We can inhibit that ack and only do it if it was requested
552 * which would be slightly cheaper, but we'd have to be careful
553 * of the order of updating our page state.
554 */
555 if (ioctl(mis->userfault_fd, UFFDIO_COPY, &copy_struct)) {
556 int e = errno;
557 error_report("%s: %s copy host: %p from: %p (size: %zd)",
558 __func__, strerror(e), host, from, pagesize);
559
560 return -e;
561 }
562
563 trace_postcopy_place_page(host);
564 return 0;
565 }
566
567 /*
568 * Place a zero page at (host) atomically
569 * returns 0 on success
570 */
571 int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
572 size_t pagesize)
573 {
574 trace_postcopy_place_page_zero(host);
575
576 if (pagesize == getpagesize()) {
577 struct uffdio_zeropage zero_struct;
578 zero_struct.range.start = (uint64_t)(uintptr_t)host;
579 zero_struct.range.len = getpagesize();
580 zero_struct.mode = 0;
581
582 if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) {
583 int e = errno;
584 error_report("%s: %s zero host: %p",
585 __func__, strerror(e), host);
586
587 return -e;
588 }
589 } else {
590 /* The kernel can't use UFFDIO_ZEROPAGE for hugepages */
591 if (!mis->postcopy_tmp_zero_page) {
592 mis->postcopy_tmp_zero_page = mmap(NULL, mis->largest_page_size,
593 PROT_READ | PROT_WRITE,
594 MAP_PRIVATE | MAP_ANONYMOUS,
595 -1, 0);
596 if (mis->postcopy_tmp_zero_page == MAP_FAILED) {
597 int e = errno;
598 mis->postcopy_tmp_zero_page = NULL;
599 error_report("%s: %s mapping large zero page",
600 __func__, strerror(e));
601 return -e;
602 }
603 memset(mis->postcopy_tmp_zero_page, '\0', mis->largest_page_size);
604 }
605 return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page,
606 pagesize);
607 }
608
609 return 0;
610 }
611
612 /*
613 * Returns a target page of memory that can be mapped at a later point in time
614 * using postcopy_place_page
615 * The same address is used repeatedly, postcopy_place_page just takes the
616 * backing page away.
617 * Returns: Pointer to allocated page
618 *
619 */
620 void *postcopy_get_tmp_page(MigrationIncomingState *mis)
621 {
622 if (!mis->postcopy_tmp_page) {
623 mis->postcopy_tmp_page = mmap(NULL, mis->largest_page_size,
624 PROT_READ | PROT_WRITE, MAP_PRIVATE |
625 MAP_ANONYMOUS, -1, 0);
626 if (mis->postcopy_tmp_page == MAP_FAILED) {
627 mis->postcopy_tmp_page = NULL;
628 error_report("%s: %s", __func__, strerror(errno));
629 return NULL;
630 }
631 }
632
633 return mis->postcopy_tmp_page;
634 }
635
636 #else
637 /* No target OS support, stubs just fail */
638 bool postcopy_ram_supported_by_host(void)
639 {
640 error_report("%s: No OS support", __func__);
641 return false;
642 }
643
644 int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
645 {
646 error_report("postcopy_ram_incoming_init: No OS support");
647 return -1;
648 }
649
650 int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
651 {
652 assert(0);
653 return -1;
654 }
655
656 int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
657 {
658 assert(0);
659 return -1;
660 }
661
662 int postcopy_ram_enable_notify(MigrationIncomingState *mis)
663 {
664 assert(0);
665 return -1;
666 }
667
668 int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
669 size_t pagesize)
670 {
671 assert(0);
672 return -1;
673 }
674
675 int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
676 size_t pagesize)
677 {
678 assert(0);
679 return -1;
680 }
681
682 void *postcopy_get_tmp_page(MigrationIncomingState *mis)
683 {
684 assert(0);
685 return NULL;
686 }
687
688 #endif
689
690 /* ------------------------------------------------------------------------- */
691
692 /**
693 * postcopy_discard_send_init: Called at the start of each RAMBlock before
694 * asking to discard individual ranges.
695 *
696 * @ms: The current migration state.
697 * @offset: the bitmap offset of the named RAMBlock in the migration
698 * bitmap.
699 * @name: RAMBlock that discards will operate on.
700 *
701 * returns: a new PDS.
702 */
703 PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms,
704 unsigned long offset,
705 const char *name)
706 {
707 PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState));
708
709 if (res) {
710 res->ramblock_name = name;
711 res->offset = offset;
712 }
713
714 return res;
715 }
716
717 /**
718 * postcopy_discard_send_range: Called by the bitmap code for each chunk to
719 * discard. May send a discard message, may just leave it queued to
720 * be sent later.
721 *
722 * @ms: Current migration state.
723 * @pds: Structure initialised by postcopy_discard_send_init().
724 * @start,@length: a range of pages in the migration bitmap in the
725 * RAM block passed to postcopy_discard_send_init() (length=1 is one page)
726 */
727 void postcopy_discard_send_range(MigrationState *ms, PostcopyDiscardState *pds,
728 unsigned long start, unsigned long length)
729 {
730 size_t tp_bits = qemu_target_page_bits();
731 /* Convert to byte offsets within the RAM block */
732 pds->start_list[pds->cur_entry] = (start - pds->offset) << tp_bits;
733 pds->length_list[pds->cur_entry] = length << tp_bits;
734 trace_postcopy_discard_send_range(pds->ramblock_name, start, length);
735 pds->cur_entry++;
736 pds->nsentwords++;
737
738 if (pds->cur_entry == MAX_DISCARDS_PER_COMMAND) {
739 /* Full set, ship it! */
740 qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
741 pds->ramblock_name,
742 pds->cur_entry,
743 pds->start_list,
744 pds->length_list);
745 pds->nsentcmds++;
746 pds->cur_entry = 0;
747 }
748 }
749
750 /**
751 * postcopy_discard_send_finish: Called at the end of each RAMBlock by the
752 * bitmap code. Sends any outstanding discard messages, frees the PDS
753 *
754 * @ms: Current migration state.
755 * @pds: Structure initialised by postcopy_discard_send_init().
756 */
757 void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds)
758 {
759 /* Anything unsent? */
760 if (pds->cur_entry) {
761 qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
762 pds->ramblock_name,
763 pds->cur_entry,
764 pds->start_list,
765 pds->length_list);
766 pds->nsentcmds++;
767 }
768
769 trace_postcopy_discard_send_finish(pds->ramblock_name, pds->nsentwords,
770 pds->nsentcmds);
771
772 g_free(pds);
773 }