Questions about private file locks (Re: Proposed new krb5 FILE ccache protocol)

Nico Williams nico at
Wed Jan 29 00:27:00 EST 2014

On Tue, Jan 28, 2014 at 7:21 PM, Greg Hudson <ghudson at> wrote:
> [1]

That's very nice.  A few questions (I hope Simo or others can relay to
the relevant engineers):

 - Do private locks share the same namespace as POSIX file locks?
Surely they must, for many reasons, among others that otherwise NFS
will not support private locks for many, many years.

 - What is to be returned in the l_pid field of struct flock when
using F_GETLKP?

   My advice: put in a constant, say, (pid_t)-1.

 - The blog says that private locks "are owned by the open file".
Does this carry through to dup()/dup2()/...?

   Also, what if the same file is opened through several distinct
open()s in the same process?

   My guess: it doesn't matter, just explicitly drop locks rather than
close(2) to drop locks.  But this should be specified, even if to say
that this is undefined.


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