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Re: [Qemu-devel] [PATCH 0/4] block: Drop BDS.filename

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH 0/4] block: Drop BDS.filename
Date: Tue, 3 Feb 2015 15:40:58 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 03.02.2015 um 14:48 hat Max Reitz geschrieben:
> On 2015-02-03 at 04:32, Kevin Wolf wrote:
> >Am 24.09.2014 um 21:48 hat Max Reitz geschrieben:
> >>The BDS filename field is generally only used when opening disk images
> >>or emitting error or warning messages, the only exception to this rule
> >>is the map command of qemu-img. However, using exact_filename there
> >>instead should not be a problem. Therefore, we can drop the filename
> >>field from the BlockDriverState and use a function instead which builds
> >>the filename from scratch when called.
> >>
> >>This is slower than reading a static char array but the problem of that
> >>static array is that it may become obsolete due to changes in any
> >>BlockDriverState or in the BDS graph. Using a function which rebuilds
> >>the filename every time it is called resolves this problem.
> >>
> >>The disadvantage of worse performance is negligible, on the other hand.
> >>After patch 2 of this series, which replaces some queries of
> >>BDS.filename by reads from somewhere else (mostly BDS.exact_filename),
> >>the filename field is only used when a disk image is opened or some
> >>message should be emitted, both of which cases do not suffer from the
> >>performance hit.
> >Surprisingly (or not), this one needs rebasing.
> Well...
> >I tried it and it doesn't look too hard, but it's a little bit more than
> >what I'm comfortable with doing while applying a series.
> I admire your courage, but I'm not sure whether this series is ready
> for being applied at all. First we (or I) will have to look into how
> users like libvirt which identify a BDS based on the filename can
> break from applying this series.

Well, I haven't reviewed it, so I can't tell. It didn't have a
(Self-)NACK and it's still on your list of to-be-merged patches, so I
took a look.  You're talking about courage - but I just wasn't
courageous enough yet to attack your larger series... ;-)


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