Re: [Qemu-devel] [PATCH 1/1] block/vpc.c: Detect too-large vpc file

[Kevin Wolf <kwolf@redhat.com>]

Am 26.07.2011 22:26, schrieb Serge E. Hallyn:
> Quoting Kevin Wolf (kwolf@redhat.com):
>> I think that footer->size contains the real size. Maybe we should do
>> something like this:
>> if (footer->size > 65536 * 16 * 255 * 512) {
>>     bs->total_sectors = footer->size / 512;
>> } else {
>>     bs->total_sectors = (int64_t)
>>         be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl
>> }
> 
> The footer->size appears to be double the 'real' size.  So I'm actually doing
> the blow.  Does this seem sensible?

Just looked it up in the spec:

"Current Size
This field stores the current size of the hard disk, in bytes, from the
perspective of the virtual machine.
This value is same as the original size when the hard disk is created.
This value can change depending on whether the hard disk is expanded."

And for the part about using CHS:

"When a hard disk is configured as an ATA hard disk, the CHS values
(that is, Cylinder, Heads, Sectors per track) are used by the ATA
controller to determine the size of the disk. When the user creates a
hard disk of a certain size, the size of the hard disk image in the
virtual machine is smaller than that created by the user. This is
because CHS value calculated from the hard disk size is rounded down."

Kevin