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

[Max Reitz <mreitz@redhat.com>]

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.

Max