Re: cp(1) fails to copy file from /proc

[Mike Frysinger]

On Thursday 23 April 2009 15:35:20 Jim Meyering wrote:
> Jim Meyering wrote:
> > Mike Frysinger wrote:
> >> On Friday 17 April 2009 18:28:07 James Youngman wrote:
> >
> > ...
> >
> >>> The patch itself looks good, but it might be worth leaving in a
> >>> comment indicating why the optimisation should not be reintroduced...
> >>
> >> and/or a new test (i prefer the "and"):
> >>  if [ -e /proc/cpuinfo ] ; then
> >>    cp /proc/cpuinfo cpuinfo.cp
> >>    cat /proc/cpuinfo > cpuinfo.cat
> >>    cmp cpuinfo.cp cpuinfo.cat
> >>  fi
> >
> > Of course ;-)
> > As promised, I've added a test for this below.
> >
> > We can't use /proc/cpuinfo, at least not precisely like that,
> > because its cpu speed line can change due to frequency scaling.
> > Also, that file is usually too small to trigger the failure.
> >
> > Here's a more complete patch, with a title and NEWS reflecting
> > that I now think it's a linux kernel bug.
> > I'll wait a few days before pushing, in case I learn otherwise.
>
> No one claims that /proc is POSIX compliant, so I'm pushing this.

wrt to stat(), sure, Linux rarely fills in the right size value.  wrt to 
read(), i'm pretty sure /proc behavior is POSIX compliant.
-mike

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