The attached patch, restores support for writable block devices using
Virtual FAT disk images.
RW support using a generated qcow base image was modified after qemu 0.8.2
was released; while adding AIO support to block-qcow.c in release 1.8; and
resulting in a broken qcow image based in an inexistent "fat:" base
when "fat:rw" was requested.
Carlo
Index: block-qcow.c
===================================================================
RCS file: /sources/qemu/qemu/block-qcow.c,v
retrieving revision 1.15
diff -u -r1.15 block-qcow.c
--- block-qcow.c 11 Nov 2007 02:51:16 -0000 1.15
+++ block-qcow.c 11 Mar 2008 07:29:00 -0000
@@ -752,11 +752,15 @@
header_size = sizeof(header);
backing_filename_len = 0;
if (backing_file) {
- header.backing_file_offset = cpu_to_be64(header_size);
- backing_filename_len = strlen(backing_file);
- header.backing_file_size = cpu_to_be32(backing_filename_len);
- header_size += backing_filename_len;
- header.mtime = cpu_to_be32(0);
+ if (strcmp(backing_file, "fat:")) {
+ header.backing_file_offset = cpu_to_be64(header_size);
+ backing_filename_len = strlen(backing_file);
+ header.backing_file_size = cpu_to_be32(backing_filename_len);
+ header_size += backing_filename_len;
+ } else {
+ /* special backing file for vvfat */
+ backing_file = NULL;
+ }
header.cluster_bits = 9; /* 512 byte cluster to avoid copying
unmodifyed sectors */
header.l2_bits = 12; /* 32 KB L2 tables */
