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

[Connor Kuehl]

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