Re: [Qemu-devel] [Qemu-block] [PATCH] block: Don't lock /dev/null and /dev/zero automatically

[Eric Blake]

On 07/20/2018 03:24 AM, Fam Zheng wrote:
> On Thu, 07/19 13:57, John Snow wrote:
> > Should we instead modify the test in this case to not attempt to take a
> > lock on a device we know cannot meaningfully store state, or is it your
> > preference to attempt to maintain such a list in the raw driver itself?
> >
> > I guess we never want QEMU to try to lock things like /dev/zero, but I
> > don't know if there are more such pseudo-devices we should never try to
> > lock and if so, what common property unifies them such that we don't
> > have to maintain a list.
>
> They are 0 sized anyway so I only expect them to be used in test cases like the
> one we're fixing. So this really doesn't matter.  An exceptional one would be
> /dev/nullb* but that is not used in real world either.

I'm not familiar with /dev/nullb* - is that a typo?

$ ll /dev/nullb*
ls: cannot access '/dev/nullb*': No such file or directory


> I'm not trying to maintain a complete list (e.g. /dev/urandom and /dev/nullb*
> are missing), this patch is just trying to make writing test code easier.

/dev/urandom is also a character device, and also fits in my heuristic 
that we likely only care about locking of block devices.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org