Re: [Qemu-devel] [PATCH 1/2] qemu-img: Allow source cache mode specification

[Kevin Wolf]

Am 22.07.2014 um 22:06 hat Max Reitz geschrieben:
> On 21.07.2014 17:52, Eric Blake wrote:
> >On 07/19/2014 02:35 PM, Max Reitz wrote:
> >>Many qemu-img subcommands only read the source file(s) once. For these
> >>use cases, a full write-back cache is unnecessary and mainly clutters
> >>host cache memory. Though this is generally no concern as cache memory
> >>is freely available and can be scaled by the host OS, it may become a
> >>concern with thin provisioning.
> >>
> >>For these cases, it makes sense to allow users to freely specify the
> >>source cache mode (e.g. use no cache at all).
> >>
> >>This commit adds a new switch (-T) for the qemu-img subcommands check,
> >>compare, convert and rebase to specify the cache to be used for source
> >>images (the backing file in case of rebase).
> >What mnemonic did you have in mind when choosing -T? Or was it just a
> >universally available letter for the subcommands you were touching?
> 
> To be honest, I just didn't know what -t stands for. Therefore I
> just thought it might be remotely logical if the lower-cased letter
> is used for destination and the upper-cased letter for source
> caching.

Things might get a bit confusing there, though, because upper-case
often means the "other image", i.e. destination or backing file, in other
commands (create -F, compare -F, convert -O and -B, rebase -F).

Of course, most of them are deprecated, so I wouldn't make that a reason
to block this series, but perhaps we should consider using more long
options instead of randomly assigning the letters that are still free.

Kevin