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Re: [Qemu-block] [PATCH v15 21/21] qemu-iotests: Add test case 153 for i


From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH v15 21/21] qemu-iotests: Add test case 153 for image locking
Date: Thu, 27 Apr 2017 11:05:10 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 27.04.2017 um 03:32 hat Fam Zheng geschrieben:
> On Wed, 04/26 16:49, Kevin Wolf wrote:
> > Am 26.04.2017 um 05:34 hat Fam Zheng geschrieben:
> > > Signed-off-by: Fam Zheng <address@hidden>
> > 
> > I'll do the actual review of the test case later, but I already have a
> > question... Can we find a way to accept the expected lock losses on
> > systems without OFD? I'm using RHEL 7 as my main development OS, so I
> > wouldn't like having to deal with false positives there.
> 
> Split the lock loss cases to a separate case and _not_run? :)

You still need to find out from a shell script whether OFD locks are
supported before you can call _not_run, but otherwise I'm fine with
this.

> > Hm... And actually, printing a warning will probably invalidate all the
> > other reference outputs, too. After all, every single invocation of
> > qemu/qemu-img/qemu-io will print a warning. Maybe that's a bit too much
> > even for manual users when they can't do anything about it (which is
> > unlike the format probing warning that you can get rid of by simply
> > changing your command line).
> 
> An idea: make locking=on/off/auto, and auto is on iff OFD is usable,
> otherwise off. When user specifies locking=on but OFD is unusable, we
> print a warning.
> 
> Only in this on test case the warning will be printed on RHEL, and
> it's easy to filter it out.

So POSIX locks only if you explicitly enable locking? It would be a pity
to do even less than we could theoretically do by default, but at least
the default wouldn't result in surprising behaviour by losing locks
randomly.

The argument for it would be that being consistently unsafe is better
than being unpredictably safe or unsafe. I always find this kind of
decision hard to make because I can appreciate both sides of the
argument.

Kevin



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