[RFC PATCH v2 3/7] migration: Use file_bmap for RAMBlock during incoming file load

[Aadeshveer Singh <aadeshveer07@gmail.com>]

Replace the temporary bitmap with the existing file_bmap attribute of
the RAMBlock. This acts as a preparatory change for the upcoming fast
snapshot load feature.

Reusing this bitmap allows the destination to track page types during
a postcopy load, enabling faster, direct placement of zero pages.

Since file_bmap is currently only utilized during the migration save
phase, it can be safely repurposed during the load phase without
introducing conflicts.

Signed-off-by: Aadeshveer Singh <aadeshveer07@gmail.com>
---
 migration/ram.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index fc38ffbf8a..4728f14d73 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -252,6 +252,17 @@ int foreach_not_ignored_block(RAMBlockIterFunc func, void *opaque)
     return ret;
 }
 
+static void ramblock_file_bmap_init(void)
+{
+    RAMBlock *rb;
+
+    RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
+        assert(!rb->file_bmap);
+        size_t size = rb->max_length >> qemu_target_page_bits();
+        rb->file_bmap = bitmap_new(size);
+    }
+}
+
 static void ramblock_recv_map_init(void)
 {
     RAMBlock *rb;
@@ -3749,6 +3760,9 @@ static int ram_load_setup(QEMUFile *f, void *opaque, Error **errp)
 {
     xbzrle_load_setup();
     ramblock_recv_map_init();
+    if (migrate_mapped_ram()) {
+        ramblock_file_bmap_init();
+    }
 
     return 0;
 }
@@ -3766,8 +3780,8 @@ static int ram_load_cleanup(void *opaque)
     xbzrle_load_cleanup();
 
     RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
-        g_free(rb->receivedmap);
-        rb->receivedmap = NULL;
+        g_clear_pointer(&rb->receivedmap, g_free);
+        g_clear_pointer(&rb->file_bmap, g_free);
     }
 
     return 0;
@@ -4142,11 +4156,18 @@ err:
 static void parse_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
                                       ram_addr_t length, Error **errp)
 {
-    g_autofree unsigned long *bitmap = NULL;
     MappedRamHeader header;
     size_t bitmap_size;
     long num_pages;
 
+    if (length > block->max_length) {
+        error_setg(errp,
+                   "mapped-ram header length %" PRIu64 " exceeds "
+                   "RAMBlock(\"%s\") max_length %" PRIu64,
+                   (uint64_t)length, block->idstr, (uint64_t)block->max_length);
+        return;
+    }
+
     if (!mapped_ram_read_header(f, &header, errp)) {
         return;
     }
@@ -4174,14 +4195,14 @@ static void parse_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
     num_pages = length / header.page_size;
     bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
 
-    bitmap = g_malloc0(bitmap_size);
-    if (qemu_get_buffer_at(f, (uint8_t *)bitmap, bitmap_size,
+    if (qemu_get_buffer_at(f, (uint8_t *)block->file_bmap, bitmap_size,
                            header.bitmap_offset) != bitmap_size) {
         error_setg(errp, "Error reading dirty bitmap");
         return;
     }
 
-    if (!read_ramblock_mapped_ram(f, block, num_pages, bitmap, errp)) {
+    if (!read_ramblock_mapped_ram(f, block, num_pages, block->file_bmap,
+                                  errp)) {
         return;
     }
 
-- 
2.54.0