[OE-core] [PATCH 08/20] udev-cache: Create cache asynchronously

[Otavio Salvador]

On Mon, Aug 4, 2014 at 6:18 PM, Richard Tollerton <rich.tollerton at ni.com> wrote:
> Otavio Salvador <otavio at ossystems.com.br> writes:
>
>> I am not sure about this one. I see the value you are adding here but
>> I worry how often something can be connected during this process and
>> change the contents along the way. Did you see something as that
>> during your tests?
>
> No, but point taken. I didn't really test "physical" hotplug during
> bootup -- and in particular, for this to be a persisting issue, the
> added/removed device must be removed/added during this boot -- but I
> suppose that is totally possible.
>
> This reflects an underlying race condition, starting at the computation
> of NEWDATA/OLDDATA in the udev initscript, and ending in the tarball
> creation in udev-cache. I suppose that we can mitigate this by spinning
> in udev-cache until the devcache stops changing...? Cheesy, untested,
> dirty RFC follows:

You need to check the list of files taken by 'tar' and compare. This
mitigates it but does not really solves the issue.

Maybe we could "copy" the nodes to a tmp area and use this as a
snapshot? The copy should be fast and makes it mostly "atomic".

-- 
Otavio Salvador                             O.S. Systems
http://www.ossystems.com.br        http://code.ossystems.com.br
Mobile: +55 (53) 9981-7854            Mobile: +1 (347) 903-9750