dump: add APIs to operate DataCache

DataCache is used to store data temporarily, then the data will be written to
vmcore. These functions will be called later when writing data of page to
vmcore.

Signed-off-by: Qiao Nuohan <qiaonuohan@cn.fujitsu.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

dump.c

@@ -1165,6 +1165,53 @@ out:
     return ret;
 }
 
+static void prepare_data_cache(DataCache *data_cache, DumpState *s,
+                               off_t offset)
+{
+    data_cache->fd = s->fd;
+    data_cache->data_size = 0;
+    data_cache->buf_size = BUFSIZE_DATA_CACHE;
+    data_cache->buf = g_malloc0(BUFSIZE_DATA_CACHE);
+    data_cache->offset = offset;
+}
+
+static int write_cache(DataCache *dc, const void *buf, size_t size,
+                       bool flag_sync)
+{
+    /*
+     * dc->buf_size should not be less than size, otherwise dc will never be
+     * enough
+     */
+    assert(size <= dc->buf_size);
+
+    /*
+     * if flag_sync is set, synchronize data in dc->buf into vmcore.
+     * otherwise check if the space is enough for caching data in buf, if not,
+     * write the data in dc->buf to dc->fd and reset dc->buf
+     */
+    if ((!flag_sync && dc->data_size + size > dc->buf_size) ||
+        (flag_sync && dc->data_size > 0)) {
+        if (write_buffer(dc->fd, dc->offset, dc->buf, dc->data_size) < 0) {
+            return -1;
+        }
+
+        dc->offset += dc->data_size;
+        dc->data_size = 0;
+    }
+
+    if (!flag_sync) {
+        memcpy(dc->buf + dc->data_size, buf, size);
+        dc->data_size += size;
+    }
+
+    return 0;
+}
+
+static void free_data_cache(DataCache *data_cache)
+{
+    g_free(data_cache->buf);
+}
+
 static ram_addr_t get_start_block(DumpState *s)
 {
     GuestPhysBlock *block;

include/sysemu/dump.h

@@ -41,6 +41,7 @@
 #define DISKDUMP_HEADER_BLOCKS      (1)
 #define BUFSIZE_BITMAP              (TARGET_PAGE_SIZE)
 #define PFN_BUFBITMAP               (CHAR_BIT * BUFSIZE_BITMAP)
+#define BUFSIZE_DATA_CACHE          (TARGET_PAGE_SIZE * 4)
 
 typedef struct ArchDumpInfo {
     int d_machine;  /* Architecture */
@@ -142,6 +143,14 @@ typedef struct QEMU_PACKED KdumpSubHeader64 {
     uint64_t max_mapnr_64;          /* header_version 6 and later */
 } KdumpSubHeader64;
 
+typedef struct DataCache {
+    int fd;             /* fd of the file where to write the cached data */
+    uint8_t *buf;       /* buffer for cached data */
+    size_t buf_size;    /* size of the buf */
+    size_t data_size;   /* size of cached data in buf */
+    off_t offset;       /* offset of the file */
+} DataCache;
+
 struct GuestPhysBlockList; /* memory_mapping.h */
 int cpu_get_dump_info(ArchDumpInfo *info,
                       const struct GuestPhysBlockList *guest_phys_blocks);