[Qemu-block] [PATCH 3/4] block/vpc: give option to force the current_size field in .bdrv_create

[Jeff Cody]

When QEMU creates a VHD image, it goes by the original spec,
calculating the current_size based on the nearest CHS geometry (with an
exception for disks > 127GB).

Apparently, Azure will only allow images that are sized to the nearest
MB, and the current_size as calculated from CHS cannot guarantee that.

Allow QEMU to create images similar to how Hyper-V creates images, by
setting current_size to the specified virtual disk size.  This
introduces an option, force_size, to be passed to the vpc format during
image creation, e.g.:

    qemu-img convert -f raw -o force_size -O vpc test.img test.vhd

Bug reference: https://bugs.launchpad.net/qemu/+bug/1490611

Signed-off-by: Jeff Cody <address@hidden>
---
 block/vpc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/block/vpc.c b/block/vpc.c
index 54a38a7..48ef16e 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -49,6 +49,8 @@ enum vhd_type {
 #define VHD_MAX_SECTORS       (65535LL * 255 * 255)
 #define VHD_MAX_GEOMETRY      (65535LL *  16 * 255)
 
+#define VPC_OPT_FORCE_SIZE "force_size"
+
 // always big-endian
 typedef struct vhd_footer {
     char        creator[8]; // "conectix"
@@ -850,6 +852,7 @@ static int vpc_create(const char *filename, QemuOpts *opts, 
Error **errp)
     int64_t total_size;
     int disk_type;
     int ret = -EIO;
+    bool force_size;
     Error *local_err = NULL;
     BlockDriverState *bs = NULL;
 
@@ -870,6 +873,8 @@ static int vpc_create(const char *filename, QemuOpts *opts, 
Error **errp)
         disk_type = VHD_DYNAMIC;
     }
 
+    force_size = qemu_opt_get_bool_del(opts, VPC_OPT_FORCE_SIZE, false);
+
     ret = bdrv_create_file(filename, opts, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
@@ -896,7 +901,8 @@ static int vpc_create(const char *filename, QemuOpts *opts, 
Error **errp)
         calculate_geometry(total_sectors + i, &cyls, &heads, &secs_per_cyl);
     }
 
-    if ((int64_t)cyls * heads * secs_per_cyl == VHD_MAX_GEOMETRY) {
+    if ((int64_t)cyls * heads * secs_per_cyl == VHD_MAX_GEOMETRY ||
+            force_size) {
         total_sectors = total_size / BDRV_SECTOR_SIZE;
         /* Allow a maximum disk size of approximately 2 TB */
         if (total_sectors > VHD_MAX_SECTORS) {
@@ -994,6 +1000,13 @@ static QemuOptsList vpc_create_opts = {
                 "Type of virtual hard disk format. Supported formats are "
                 "{dynamic (default) | fixed} "
         },
+        {
+            .name = VPC_OPT_FORCE_SIZE,
+            .type = QEMU_OPT_BOOL,
+            .help = "Force disk size calculation to use the actual size "
+                    "specified, rather than using the nearest CHS-based "
+                    "calculation"
+        },
         { /* end of list */ }
     }
 };
-- 
1.9.3