Re: [PATCH] Document qemu-img options data_file and data_file_raw

[Connor Kuehl <ckuehl@redhat.com>]

On 3/23/21 6:15 PM, John Snow wrote:
> On 3/1/21 12:28 PM, Connor Kuehl wrote:
>> [..]
>> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
>> index b615aa8419..5cc585dc27 100644
>> --- a/docs/tools/qemu-img.rst
>> +++ b/docs/tools/qemu-img.rst
>> @@ -866,6 +866,18 @@ Supported image file formats:
>>       issue ``lsattr filename`` to check if the NOCOW flag is set or not
>>       (Capital 'C' is NOCOW flag).
>> +  ``data_file``
>> +    Pathname that refers to a file that will store all guest data. If
>> +    this option is used, the qcow2 file will only contain the image's
>> +    metadata.
>> +
> 
> Might recommend "filename" simply for parity with *FILENAME* argument.
> 
> (This is the first appearance of "Pathname" in this file without spaces, 
> though "Path name" is indeed used several times.)
> 
>> +  ``data_file_raw``
>> +    If this option is set to ``on``, QEMU will always keep the external
>> +    data file consistent as a standalone read-only raw image. The 
>> default
>> +    value is ``off``.
>> +
>> +    This option can only be enabled if ``data_file`` is set.
>> +
> 
> How does this interact with caching options, if it does? What happens in 
> the negative case -- how does the file become inconsistent?

Hi,

First, just wanted to share the same note I'm sending to Max's review:

> Hey, I just wanted to leave a note indicating that I'm not ignoring this review; I've incorporated it in my next version but I am waiting until after the freeze to send it.

Second: I've been trying to figure out if and how this affects caching. 
I do not know yet. I will keep digging. My next version of the patch 
does touch on the negative case though, describing how it becomes 
inconsistent.

Thank you!

Connor