migration/ram: Add outgoing 'mapped-ram' migration
Implement the outgoing migration side for the 'mapped-ram' capability. A bitmap is introduced to track which pages have been written in the migration file. Pages are written at a fixed location for every ramblock. Zero pages are ignored as they'd be zero in the destination migration as well. The migration stream is altered to put the dirty pages for a ramblock after its header instead of having a sequential stream of pages that follow the ramblock headers. Without mapped-ram (current): With mapped-ram (new): --------------------- -------------------------------- | ramblock 1 header | | ramblock 1 header | --------------------- -------------------------------- | ramblock 2 header | | ramblock 1 mapped-ram header | --------------------- -------------------------------- | ... | | padding to next 1MB boundary | --------------------- | ... | | ramblock n header | -------------------------------- --------------------- | ramblock 1 pages | | RAM_SAVE_FLAG_EOS | | ... | --------------------- -------------------------------- | stream of pages | | ramblock 2 header | | (iter 1) | -------------------------------- | ... | | ramblock 2 mapped-ram header | --------------------- -------------------------------- | RAM_SAVE_FLAG_EOS | | padding to next 1MB boundary | --------------------- | ... | | stream of pages | -------------------------------- | (iter 2) | | ramblock 2 pages | | ... | | ... | --------------------- -------------------------------- | ... | | ... | --------------------- -------------------------------- | RAM_SAVE_FLAG_EOS | -------------------------------- | ... | -------------------------------- where: - ramblock header: the generic information for a ramblock, such as idstr, used_len, etc. - ramblock mapped-ram header: the new information added by this feature: bitmap of pages written, bitmap size and offset of pages in the migration file. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Fabiano Rosas <farosas@suse.de> Link: https://lore.kernel.org/r/20240229153017.2221-10-farosas@suse.de Signed-off-by: Peter Xu <peterx@redhat.com>
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@ -44,6 +44,19 @@ struct RAMBlock {
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size_t page_size;
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/* dirty bitmap used during migration */
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unsigned long *bmap;
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/*
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* Below fields are only used by mapped-ram migration
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*/
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/* bitmap of pages present in the migration file */
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unsigned long *file_bmap;
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/*
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* offset in the file pages belonging to this ramblock are saved,
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* used only during migration to a file.
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*/
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off_t bitmap_offset;
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uint64_t pages_offset;
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/* bitmap of already received pages in postcopy */
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unsigned long *receivedmap;
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117
migration/ram.c
117
migration/ram.c
@ -94,6 +94,18 @@
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#define RAM_SAVE_FLAG_MULTIFD_FLUSH 0x200
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/* We can't use any flag that is bigger than 0x200 */
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/*
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* mapped-ram migration supports O_DIRECT, so we need to make sure the
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* userspace buffer, the IO operation size and the file offset are
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* aligned according to the underlying device's block size. The first
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* two are already aligned to page size, but we need to add padding to
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* the file to align the offset. We cannot read the block size
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* dynamically because the migration file can be moved between
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* different systems, so use 1M to cover most block sizes and to keep
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* the file offset aligned at page size as well.
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*/
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#define MAPPED_RAM_FILE_OFFSET_ALIGNMENT 0x100000
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XBZRLECacheStats xbzrle_counters;
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/* used by the search for pages to send */
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@ -1126,12 +1138,18 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
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return 0;
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}
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stat64_add(&mig_stats.zero_pages, 1);
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if (migrate_mapped_ram()) {
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/* zero pages are not transferred with mapped-ram */
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clear_bit(offset >> TARGET_PAGE_BITS, pss->block->file_bmap);
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return 1;
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}
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len += save_page_header(pss, file, pss->block, offset | RAM_SAVE_FLAG_ZERO);
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qemu_put_byte(file, 0);
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len += 1;
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ram_release_page(pss->block->idstr, offset);
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stat64_add(&mig_stats.zero_pages, 1);
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ram_transferred_add(len);
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/*
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@ -1189,6 +1207,11 @@ static int save_normal_page(PageSearchStatus *pss, RAMBlock *block,
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{
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QEMUFile *file = pss->pss_channel;
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if (migrate_mapped_ram()) {
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qemu_put_buffer_at(file, buf, TARGET_PAGE_SIZE,
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block->pages_offset + offset);
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set_bit(offset >> TARGET_PAGE_BITS, block->file_bmap);
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} else {
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ram_transferred_add(save_page_header(pss, pss->pss_channel, block,
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offset | RAM_SAVE_FLAG_PAGE));
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if (async) {
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@ -1198,6 +1221,7 @@ static int save_normal_page(PageSearchStatus *pss, RAMBlock *block,
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} else {
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qemu_put_buffer(file, buf, TARGET_PAGE_SIZE);
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}
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}
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ram_transferred_add(TARGET_PAGE_SIZE);
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stat64_add(&mig_stats.normal_pages, 1);
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return 1;
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@ -2411,6 +2435,8 @@ static void ram_save_cleanup(void *opaque)
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block->clear_bmap = NULL;
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g_free(block->bmap);
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block->bmap = NULL;
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g_free(block->file_bmap);
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block->file_bmap = NULL;
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}
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xbzrle_cleanup();
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@ -2778,6 +2804,9 @@ static void ram_list_init_bitmaps(void)
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*/
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block->bmap = bitmap_new(pages);
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bitmap_set(block->bmap, 0, pages);
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if (migrate_mapped_ram()) {
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block->file_bmap = bitmap_new(pages);
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}
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block->clear_bmap_shift = shift;
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block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
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}
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@ -2915,6 +2944,60 @@ void qemu_guest_free_page_hint(void *addr, size_t len)
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}
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}
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#define MAPPED_RAM_HDR_VERSION 1
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struct MappedRamHeader {
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uint32_t version;
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/*
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* The target's page size, so we know how many pages are in the
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* bitmap.
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*/
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uint64_t page_size;
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/*
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* The offset in the migration file where the pages bitmap is
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* stored.
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*/
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uint64_t bitmap_offset;
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/*
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* The offset in the migration file where the actual pages (data)
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* are stored.
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*/
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uint64_t pages_offset;
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} QEMU_PACKED;
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typedef struct MappedRamHeader MappedRamHeader;
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static void mapped_ram_setup_ramblock(QEMUFile *file, RAMBlock *block)
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{
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g_autofree MappedRamHeader *header = NULL;
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size_t header_size, bitmap_size;
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long num_pages;
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header = g_new0(MappedRamHeader, 1);
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header_size = sizeof(MappedRamHeader);
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num_pages = block->used_length >> TARGET_PAGE_BITS;
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bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
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/*
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* Save the file offsets of where the bitmap and the pages should
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* go as they are written at the end of migration and during the
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* iterative phase, respectively.
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*/
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block->bitmap_offset = qemu_get_offset(file) + header_size;
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block->pages_offset = ROUND_UP(block->bitmap_offset +
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bitmap_size,
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MAPPED_RAM_FILE_OFFSET_ALIGNMENT);
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header->version = cpu_to_be32(MAPPED_RAM_HDR_VERSION);
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header->page_size = cpu_to_be64(TARGET_PAGE_SIZE);
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header->bitmap_offset = cpu_to_be64(block->bitmap_offset);
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header->pages_offset = cpu_to_be64(block->pages_offset);
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qemu_put_buffer(file, (uint8_t *) header, header_size);
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/* prepare offset for next ramblock */
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qemu_set_offset(file, block->pages_offset + block->used_length, SEEK_SET);
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}
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/*
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* Each of ram_save_setup, ram_save_iterate and ram_save_complete has
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* long-running RCU critical section. When rcu-reclaims in the code
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@ -2964,6 +3047,10 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
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if (migrate_ignore_shared()) {
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qemu_put_be64(f, block->mr->addr);
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}
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if (migrate_mapped_ram()) {
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mapped_ram_setup_ramblock(f, block);
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}
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}
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}
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@ -2997,6 +3084,20 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
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return qemu_fflush(f);
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}
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static void ram_save_file_bmap(QEMUFile *f)
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{
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RAMBlock *block;
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RAMBLOCK_FOREACH_MIGRATABLE(block) {
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long num_pages = block->used_length >> TARGET_PAGE_BITS;
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long bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
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qemu_put_buffer_at(f, (uint8_t *)block->file_bmap, bitmap_size,
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block->bitmap_offset);
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ram_transferred_add(bitmap_size);
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}
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}
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/**
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* ram_save_iterate: iterative stage for migration
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*
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@ -3186,6 +3287,18 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
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return ret;
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}
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if (migrate_mapped_ram()) {
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ram_save_file_bmap(f);
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if (qemu_file_get_error(f)) {
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Error *local_err = NULL;
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int err = qemu_file_get_error_obj(f, &local_err);
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error_reportf_err(local_err, "Failed to write bitmap to file: ");
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return -err;
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}
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}
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if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
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qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
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}
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