Re: [coreutils] [PATCH 1/2] stat: support printing birthtime

[Eric Blake]

On 10/01/2010 09:11 AM, Jim Meyering wrote:
> Eric Blake wrote:
> ...
> > +# Whether birthtime is supported or not, it better not change even when
> > +# [acm]time are modified.  :)
> > +touch a || fail=1
> > +btime=$(stat --format %W a) || fail=1
> > +atime=$(stat --format %X a) || fail=1
> > +mtime=$(stat --format %Y a) || fail=1
> > +ctime=$(stat --format %Z a) || fail=1
> > +
> > +case $(stat --format %x a) in
> > +  *.000000000*) sleep 2;; # worst case file system is FAT
> > +  *) # FIXME: sleep .1 would be sufficient if %X showed nanoseconds
> > + sleep 1;; # should be adequate for any system with subsecond resolution
> > +esac
>
> We try hard to avoid sleeping in the common case.
> Any reason not to do what the FIXME suggests?
>
>      case $(stat --format %X a) in
>        *.000000000) sleep 1;;

You need two seconds for FAT.

>        *) sleep .1;;

Done in patch 2/2 (see my other email) - you HAVE to sleep longer than 
the minimum resolution of %X...

>      esac
>
> > +touch a || fail=1
> > +test "x$btime" = x$(stat --format %W a) || fail=1
> > +test "x$atime" != x$(stat --format %X a) || fail=1

before you can guarantee that %X changed.  But if %X doesn't print 
subsecond details (as in patch 2/2), ... :)

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org