Re: [Xen-devel] [PATCH] Fix locking in tools/hotplug/Linux/locking.sh

[Jacek Konieczny <jajcus@xxxxxxxxxx>]

On Mon, Nov 12, 2012 at 04:42:37PM +0000, Ian Campbell wrote:
> On Fri, 2012-11-09 at 13:56 +0000, Jacek Konieczny wrote:
> > The claim_lock() function would fail in the perl code with:
> > 
> >   Invalid argument at -e line 2.
> > 
> > because the Perl snippet opens for reading the file descriptor, which
> > was earlier opened for write (append).
> 
> Looks plausible to me.
> 
> How does this interact with the 
>         eval "exec $_lockfd<&-"
> which Olaf added in 26079:b3b03536789a ? I suppose close is close and
> <&- and >&- or even <>&- are equivalent?

It seems <&- and >&- are indeed the same and there is no such thing as '<>&-'.

I have added the Olaf's change to my test setup and it works properly. So
no conflict here.

> > 
> > Signed-off-by: Jacek Konieczny <jajcus@xxxxxxxxxx>
> > ---
> >  tools/hotplug/Linux/locking.sh | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/hotplug/Linux/locking.sh b/tools/hotplug/Linux/locking.sh
> > index e34f155..122bcfb 100644
> > --- a/tools/hotplug/Linux/locking.sh
> > +++ b/tools/hotplug/Linux/locking.sh
> > @@ -44,7 +44,7 @@ claim_lock()
> >      # See below for a correctness proof.
> >      local rightfile
> >      while true; do
> > -        eval "exec $_lockfd>>$_lockfile"
> > +        eval "exec $_lockfd<>$_lockfile"
> >          flock -x $_lockfd || return $?
> >          # We can't just stat /dev/stdin or /proc/self/fd/$_lockfd or
> >          # use bash's test -ef because those all go through what is

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