qcow2: implement bdrv_invalidate_cache (v2)

We don't reopen the actual file, but instead invoke the close and open routines.
We specifically ignore the backing file since it's contents are read-only and
therefore immutable.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/qcow2.c

@@ -240,6 +240,7 @@ static int qcow2_open(BlockDriverState *bs, int flags)
     s->cluster_data = qemu_blockalign(bs, QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size
                                   + 512);
     s->cluster_cache_offset = -1;
+    s->flags = flags;
 
     ret = qcow2_refcount_init(bs);
     if (ret != 0) {
@@ -632,6 +633,37 @@ static void qcow2_close(BlockDriverState *bs)
     qcow2_refcount_close(bs);
 }
 
+static void qcow2_invalidate_cache(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    int flags = s->flags;
+    AES_KEY aes_encrypt_key;
+    AES_KEY aes_decrypt_key;
+    uint32_t crypt_method = 0;
+
+    /*
+     * Backing files are read-only which makes all of their metadata immutable,
+     * that means we don't have to worry about reopening them here.
+     */
+
+    if (s->crypt_method) {
+        crypt_method = s->crypt_method;
+        memcpy(&aes_encrypt_key, &s->aes_encrypt_key, sizeof(aes_encrypt_key));
+        memcpy(&aes_decrypt_key, &s->aes_decrypt_key, sizeof(aes_decrypt_key));
+    }
+
+    qcow2_close(bs);
+
+    memset(s, 0, sizeof(BDRVQcowState));
+    qcow2_open(bs, flags);
+
+    if (crypt_method) {
+        s->crypt_method = crypt_method;
+        memcpy(&s->aes_encrypt_key, &aes_encrypt_key, sizeof(aes_encrypt_key));
+        memcpy(&s->aes_decrypt_key, &aes_decrypt_key, sizeof(aes_decrypt_key));
+    }
+}
+
 /*
  * Updates the variable length parts of the qcow2 header, i.e. the backing file
  * name and all extensions. qcow2 was not designed to allow such changes, so if
@@ -1269,6 +1301,8 @@ static BlockDriver bdrv_qcow2 = {
 
     .bdrv_change_backing_file   = qcow2_change_backing_file,
 
+    .bdrv_invalidate_cache      = qcow2_invalidate_cache,
+
     .create_options = qcow2_create_options,
     .bdrv_check = qcow2_check,
 };

block/qcow2.h

@@ -125,6 +125,8 @@ typedef struct BDRVQcowState {
     int snapshots_size;
     int nb_snapshots;
     QCowSnapshot *snapshots;
+
+    int flags;
 } BDRVQcowState;
 
 /* XXX: use std qcow open function ? */