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block/vpc: give option to force the current_size field in .bdrv_create 

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

When using the "force_size" option, the creator app field used by
QEMU will be "qem2" instead of "qemu", to indicate the difference.
In light of this, we also add parsing of the "qem2" field during
vpc_open.

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

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Jeff Cody 2016-02-25 12:27:29 -05:00 committed by Kevin Wolf
parent 798609bbe2
commit fb9245c261
1 changed files with 35 additions and 7 deletions
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42
block/vpc.c
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@ -46,8 +46,14 @@ enum vhd_type {
// Seconds since Jan 1, 2000 0:00:00 (UTC)
#define VHD_TIMESTAMP_BASE 946684800
#define VHD_CHS_MAX_C 65535LL
#define VHD_CHS_MAX_H 16
#define VHD_CHS_MAX_S 255
#define VHD_MAX_SECTORS (65535LL * 255 * 255)
#define VHD_MAX_GEOMETRY (65535LL * 16 * 255)
#define VHD_MAX_GEOMETRY (VHD_CHS_MAX_C * VHD_CHS_MAX_H * VHD_CHS_MAX_S)
#define VPC_OPT_FORCE_SIZE "force_size"
// always big-endian
typedef struct vhd_footer {
@ -288,6 +294,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
* Known creator apps:
* 'vpc ' : CHS Virtual PC (uses disk geometry)
* 'qemu' : CHS QEMU (uses disk geometry)
* 'qem2' : current_size QEMU (uses current_size)
* 'win ' : current_size Hyper-V
* 'd2v ' : current_size Disk2vhd
*
@ -296,6 +303,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
* that have CHS geometry of the maximum size.
*/
use_chs = (!!strncmp(footer->creator_app, "win ", 4) &&
!!strncmp(footer->creator_app, "qem2", 4) &&
!!strncmp(footer->creator_app, "d2v ", 4)) || s->force_use_chs;
if (!use_chs || bs->total_sectors == VHD_MAX_GEOMETRY || s->force_use_sz) {
@ -850,6 +858,7 @@ 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 +879,8 @@ 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);
@ -887,13 +898,20 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
* sectors requested until we get enough (or fail). This ensures that
* qemu-img convert doesn't truncate images, but rather rounds up.
*
* If the image size can't be represented by a spec conform CHS geometry,
* If the image size can't be represented by a spec conformant CHS geometry,
* we set the geometry to 65535 x 16 x 255 (CxHxS) sectors and use
* the image size from the VHD footer to calculate total_sectors.
*/
total_sectors = MIN(VHD_MAX_GEOMETRY, total_size / BDRV_SECTOR_SIZE);
for (i = 0; total_sectors > (int64_t)cyls * heads * secs_per_cyl; i++) {
calculate_geometry(total_sectors + i, &cyls, &heads, &secs_per_cyl);
if (force_size) {
/* This will force the use of total_size for sector count, below */
cyls = VHD_CHS_MAX_C;
heads = VHD_CHS_MAX_H;
secs_per_cyl = VHD_CHS_MAX_S;
} else {
total_sectors = MIN(VHD_MAX_GEOMETRY, total_size / BDRV_SECTOR_SIZE);
for (i = 0; total_sectors > (int64_t)cyls * heads * secs_per_cyl; i++) {
calculate_geometry(total_sectors + i, &cyls, &heads, &secs_per_cyl);
}
}
if ((int64_t)cyls * heads * secs_per_cyl == VHD_MAX_GEOMETRY) {
@ -912,8 +930,11 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
memset(buf, 0, 1024);
memcpy(footer->creator, "conectix", 8);
/* TODO Check if "qemu" creator_app is ok for VPC */
memcpy(footer->creator_app, "qemu", 4);
if (force_size) {
memcpy(footer->creator_app, "qem2", 4);
} else {
memcpy(footer->creator_app, "qemu", 4);
}
memcpy(footer->creator_os, "Wi2k", 4);
footer->features = cpu_to_be32(0x02);
@ -994,6 +1015,13 @@ 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 */ }
}
};