kvm-87: qemu-img creates raw file with wrong size

kvm-87: qemu-img creates raw file with wrong size

[Randy Smith]

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Greetings,

Running `qemu-img create -f raw file.raw 1000` creates a 512 byte file
rather than the 1000K file the docs imply.

From the help message:
"
'size' is the disk image size in kilobytes. Optional suffixes
'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 * 1024 * 1024) are
supported any 'k' or 'K' is ignored
"

Did the default change or is there bug with the create?

-- 
Randy Smith
http://www.vuser.org/
http://perlstalker.blogspot.com/


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Re: kvm-87: qemu-img creates raw file with wrong size

[Anthony Liguori]

Randy Smith wrote:
> Greetings,
>
> Running `qemu-img create -f raw file.raw 1000` creates a 512 byte file
> rather than the 1000K file the docs imply.
>
> From the help message:
> "
> 'size' is the disk image size in kilobytes. Optional suffixes
> 'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 * 1024 * 1024) are
> supported any 'k' or 'K' is ignored
> "
>
> Did the default change or is there bug with the create?
>   

No suffix assumes bytes.  It truncates to the nearest sector which is 
why you see a 512 byte file.  If you did `qemu-img create -f raw 
file.raw 1024` you would see a file of 1024 bytes.

Not sure if the docs is wrong or this behavior changed.  Patch either 
way would be appreciated/accepted.

Regards,

Anthony Liguori

Re: kvm-87: qemu-img creates raw file with wrong size

[Randall Smith]

On Mon, Jul 13, 2009 at 3:40 PM, Anthony Liguori<anthony@codemonkey.ws> wrote:
> Randy Smith wrote:
>>
>> Greetings,
>>
>> Running `qemu-img create -f raw file.raw 1000` creates a 512 byte file
>> rather than the 1000K file the docs imply.
>>
>> From the help message:
>> "
>> 'size' is the disk image size in kilobytes. Optional suffixes
>> 'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 * 1024 * 1024) are
>> supported any 'k' or 'K' is ignored
>> "
>>
>> Did the default change or is there bug with the create?
>>
>
> No suffix assumes bytes.  It truncates to the nearest sector which is why
> you see a 512 byte file.  If you did `qemu-img create -f raw file.raw 1024`
> you would see a file of 1024 bytes.
>
> Not sure if the docs is wrong or this behavior changed.  Patch either way
> would be appreciated/accepted.

It looks like the behavior changed. The ubuntu-vm-builder depended on
'size' defaulting to kilobytes and the help message printed when
qemu-img is run claims that it should default to kilobytes.

Here's a patch that updates the help message. It doesn't matter to me
if the behavior changed here but as long as the docs match what's
really happening.

--- qemu-img.c.orig	2009-07-13 15:42:49.000000000 -0600
+++ qemu-img.c	2009-07-13 15:43:11.000000000 -0600
@@ -78,7 +78,7 @@
            "    content as the input's base image, however the path,
image format, etc may\n"
            "    differ\n"
            "  'fmt' is the disk image format. It is guessed
automatically in most cases\n"
-           "  'size' is the disk image size in kilobytes. Optional suffixes\n"
+           "  'size' is the disk image size in bytes. Optional suffixes\n"
            "    'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 *
1024 * 1024) are\n"
            "    supported any 'k' or 'K' is ignored\n"
            "  'output_filename' is the destination disk image filename\n"


-- 
Randy Smith
http://www.vuser.org/
http://perlstalker.blogspot.com/

Re: kvm-87: qemu-img creates raw file with wrong size

[Lynn Kerby]

On Jul 13, 2009, at 2:48 PM, Randall Smith wrote:

> On Mon, Jul 13, 2009 at 3:40 PM, Anthony  
> Liguori<anthony@codemonkey.ws> wrote:
>> Randy Smith wrote:
>>>
>>> Greetings,
>>>
>>> Running `qemu-img create -f raw file.raw 1000` creates a 512 byte  
>>> file
>>> rather than the 1000K file the docs imply.
>>>
>>> From the help message:
>>> "
>>> 'size' is the disk image size in kilobytes. Optional suffixes
>>> 'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 * 1024 * 1024)  
>>> are
>>> supported any 'k' or 'K' is ignored
>>> "
>>>
>>> Did the default change or is there bug with the create?
>>>
>>
>> No suffix assumes bytes.  It truncates to the nearest sector which  
>> is why
>> you see a 512 byte file.  If you did `qemu-img create -f raw  
>> file.raw 1024`
>> you would see a file of 1024 bytes.
>>
>> Not sure if the docs is wrong or this behavior changed.  Patch  
>> either way
>> would be appreciated/accepted.
>
> It looks like the behavior changed. The ubuntu-vm-builder depended on
> 'size' defaulting to kilobytes and the help message printed when
> qemu-img is run claims that it should default to kilobytes.
>
> Here's a patch that updates the help message. It doesn't matter to me
> if the behavior changed here but as long as the docs match what's
> really happening.
>
> --- qemu-img.c.orig	2009-07-13 15:42:49.000000000 -0600
> +++ qemu-img.c	2009-07-13 15:43:11.000000000 -0600
> @@ -78,7 +78,7 @@
>            "    content as the input's base image, however the path,
> image format, etc may\n"
>            "    differ\n"
>            "  'fmt' is the disk image format. It is guessed
> automatically in most cases\n"
> -           "  'size' is the disk image size in kilobytes. Optional  
> suffixes\n"
> +           "  'size' is the disk image size in bytes. Optional  
> suffixes\n"
>            "    'M' (megabyte, 1024 * 1024) and 'G' (gigabyte, 1024 *
> 1024 * 1024) are\n"
>            "    supported any 'k' or 'K' is ignored\n"
>            "  'output_filename' is the destination disk image  
> filename\n"

The help message is still incorrect.  The 'k' or 'K' suffix is  
supported also and not ignored like the message says.

Lynn Kerby