block: add interface to toggle copy-on-read
The bdrv_enable_copy_on_read()/bdrv_disable_copy_on_read() functions can
be used to programmatically enable or disable copy-on-read for a block
device. Later patches add the actual copy-on-read logic.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 1643667..9b3cb75 100644
--- a/block.c
+++ b/block.c
@@ -538,6 +538,22 @@
return 0;
}
+/**
+ * The copy-on-read flag is actually a reference count so multiple users may
+ * use the feature without worrying about clobbering its previous state.
+ * Copy-on-read stays enabled until all users have called to disable it.
+ */
+void bdrv_enable_copy_on_read(BlockDriverState *bs)
+{
+ bs->copy_on_read++;
+}
+
+void bdrv_disable_copy_on_read(BlockDriverState *bs)
+{
+ assert(bs->copy_on_read > 0);
+ bs->copy_on_read--;
+}
+
/*
* Common part for opening disk images and files
*/
@@ -559,6 +575,11 @@
bs->growable = 0;
bs->buffer_alignment = 512;
+ assert(bs->copy_on_read == 0); /* bdrv_new() and bdrv_close() make it so */
+ if ((flags & BDRV_O_RDWR) && (flags & BDRV_O_COPY_ON_READ)) {
+ bdrv_enable_copy_on_read(bs);
+ }
+
pstrcpy(bs->filename, sizeof(bs->filename), filename);
bs->backing_file[0] = '\0';
@@ -801,6 +822,7 @@
#endif
bs->opaque = NULL;
bs->drv = NULL;
+ bs->copy_on_read = 0;
if (bs->file != NULL) {
bdrv_close(bs->file);