Re: [Qemu-devel] [Bug 826363] Re: qemu-img convert does not work with vdi files

[Stefan Weil <weil@mail.berlios.de>]

Am 17.08.2011 18:44, schrieb Stefan Hajnoczi:
> On Wed, Aug 17, 2011 at 5:29 PM, Stefan Hajnoczi <stefanha@gmail.com> 
> wrote:
>> On Tue, Aug 16, 2011 at 7:07 PM, Steve Si <826363@bugs.launchpad.net> 
>> wrote:
>>> I got binaries from http://homepage3.nifty.com/takeda-toshiya/
>>>
>>> tested under Win 7 64-bit as User=Administrator
>>>
>>> qemu10.6 - works  makes      16/08/2011  18:43     3,096,481,792 
>>> test.raw
>>> qemu11.1 - works  makes      16/08/2011  18:43     3,096,481,792 
>>> test.raw
>>> qemu12.1 - crashes !
>>> qemu12.2 - crashes !
>>> qemu12.5 - error while writing
>>
>> I think this crash->error transition is explained by:
>>
>> commit 8cef921d18025b4ce4e749eed391308033fee232
>> Author: TeLeMan <geleman@gmail.com>
>> Date:   Mon Feb 8 16:20:00 2010 +0800
>>
>>    qemu-img: use the heap instead of the huge stack array for win32
>>
>> But we still don't know why you are getting the write error.  It would
>> be fairly easy to find that out by building QEMU from source and
>> adding fprintf() where the write fails - print out the error code and
>> sector number.

The current code only supports images (any format) with less than
4 GiB (maybe even less than 2 GiB).

This limitation is caused by the usage of function ftruncate to create
the destination file. ftruncate takes a long (32 bit) parameter.

Linux code also uses ftruncate to create files of a certain size.
This is not a good solution. Extract from the man page:

"However, some non-native file systems do not permit truncate() and
ftruncate() to be used to extend a file beyond its current length:
a notable example on Linux is VFAT."