block: vhdx - update log guid in header, and first write tracker

Allow tracking of first file write in the VHDX image, as well as
the ability to update the GUID in the header.  This is in preparation
for log support.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/vhdx.c

@@ -230,7 +230,7 @@ static int vhdx_probe(const uint8_t *buf, int buf_size, const char *filename)
  *  - non-current header is updated with largest sequence number
  */
 static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
-                              bool generate_data_write_guid)
+                              bool generate_data_write_guid, MSGUID *log_guid)
 {
     int ret = 0;
     int hdr_idx = 0;
@@ -262,6 +262,11 @@ static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
         vhdx_guid_generate(&inactive_header->data_write_guid);
     }
 
+    /* update the log guid if present */
+    if (log_guid) {
+        inactive_header->log_guid = *log_guid;
+    }
+
     /* the header checksum is not over just the packed size of VHDXHeader,
      * but rather over the entire 'reserved' range for the header, which is
      * 4KB (VHDX_HEADER_SIZE). */
@@ -294,16 +299,16 @@ exit:
  * The VHDX spec calls for header updates to be performed twice, so that both
  * the current and non-current header have valid info
  */
-static int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s,
-                               bool generate_data_write_guid)
+int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s,
+                        bool generate_data_write_guid, MSGUID *log_guid)
 {
     int ret;
 
-    ret = vhdx_update_header(bs, s, generate_data_write_guid);
+    ret = vhdx_update_header(bs, s, generate_data_write_guid, log_guid);
     if (ret < 0) {
         return ret;
     }
-    ret = vhdx_update_header(bs, s, generate_data_write_guid);
+    ret = vhdx_update_header(bs, s, generate_data_write_guid, log_guid);
     return ret;
 }
 
@@ -784,6 +789,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
 
 
     s->bat = NULL;
+    s->first_visible_write = true;
 
     qemu_co_mutex_init(&s->lock);
 
@@ -864,7 +870,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     if (flags & BDRV_O_RDWR) {
-        ret = vhdx_update_headers(bs, s, false);
+        ret = vhdx_update_headers(bs, s, false, NULL);
         if (ret < 0) {
             goto fail;
         }
@@ -1010,6 +1016,18 @@ exit:
 
 
 
+/* Per the spec, on the first write of guest-visible data to the file the
+ * data write guid must be updated in the header */
+int vhdx_user_visible_write(BlockDriverState *bs, BDRVVHDXState *s)
+{
+    int ret = 0;
+    if (s->first_visible_write) {
+        s->first_visible_write = false;
+        ret = vhdx_update_headers(bs, s, true, NULL);
+    }
+    return ret;
+}
+
 static coroutine_fn int vhdx_co_writev(BlockDriverState *bs, int64_t sector_num,
                                       int nb_sectors, QEMUIOVector *qiov)
 {

block/vhdx.h

@@ -361,6 +361,7 @@ typedef struct BDRVVHDXState {
     VHDXBatEntry *bat;
     uint64_t bat_offset;
 
+    bool first_visible_write;
     MSGUID session_guid;
 
     VHDXLogEntries log;
@@ -373,6 +374,9 @@ typedef struct BDRVVHDXState {
 
 void vhdx_guid_generate(MSGUID *guid);
 
+int vhdx_update_headers(BlockDriverState *bs, BDRVVHDXState *s, bool rw,
+                        MSGUID *log_guid);
+
 uint32_t vhdx_update_checksum(uint8_t *buf, size_t size, int crc_offset);
 uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
                             int crc_offset);
@@ -402,4 +406,6 @@ void vhdx_log_data_le_export(VHDXLogDataSector *d);
 void vhdx_log_entry_hdr_le_import(VHDXLogEntryHeader *hdr);
 void vhdx_log_entry_hdr_le_export(VHDXLogEntryHeader *hdr);
 
+int vhdx_user_visible_write(BlockDriverState *bs, BDRVVHDXState *s);
+
 #endif