linux-kernel - RE: [Nfs-ganesha-devel] [PATCH v3 5/6] locks: report l_pid as -1 for FL_FILE

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Date:	Tue, 10 Dec 2013 11:41:04 -0800
From:	"Frank Filz" <ffilzlnx@...dspring.com>
To:	"'Jeff Layton'" <jlayton@...hat.com>
Cc:	<linux-fsdevel@...r.kernel.org>,
	<nfs-ganesha-devel@...ts.sourceforge.net>,
	<samba-technical@...ts.samba.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [Nfs-ganesha-devel] [PATCH v3 5/6] locks: report l_pid as -1	for FL_FILE_PVT locks

> On Tue, 10 Dec 2013 14:17:34 -0500
> Jeff Layton <jlayton@...hat.com> wrote:
> 
> > FL_FILE_PVT locks are no longer tied to a particular pid, and are
> > instead inheritable by child processes. Report a l_pid of '-1' for
> > these sorts of locks since the pid is somewhat meaningless for them.
> >
> > This precedent comes from FreeBSD. There, POSIX and flock() locks can
> > conflict with one another. If fcntl(F_GETLK, ...) returns a lock set
> > with flock() then the l_pid member cannot be a process ID because the
> > lock is not held by a process as such.
> >
> > Signed-off-by: Jeff Layton <jlayton@...hat.com>
> > ---
> >  fs/locks.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/locks.c b/fs/locks.c
> > index e163a30..5372ddd 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -1899,7 +1899,7 @@ EXPORT_SYMBOL_GPL(vfs_test_lock);
> >
> >  static int posix_lock_to_flock(struct flock *flock, struct file_lock
> > *fl)  {
> > -	flock->l_pid = fl->fl_pid;
> > +	flock->l_pid = IS_FILE_PVT(fl) ? -1 : fl->fl_pid;
> >  #if BITS_PER_LONG == 32
> >  	/*
> >  	 * Make sure we can represent the posix lock via @@ -1921,7 +1921,7
> > @@ static int posix_lock_to_flock(struct flock *flock, struct
> > file_lock *fl)  #if BITS_PER_LONG == 32  static void
> > posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)  {
> > -	flock->l_pid = fl->fl_pid;
> > +	flock->l_pid = IS_FILE_PVT(fl) ? -1 : fl->fl_pid;
> >  	flock->l_start = fl->fl_start;
> >  	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
> >  		fl->fl_end - fl->fl_start + 1;
> 
> While I think this behavior is reasonable, I do wonder if we ought to
consider
> more changes to how F_GETLK works. Currently the F_GETLK code won't
> handle the new l_type values, but maybe it should...
> 
> For instance, if there is a conflicting lock, and the F_GETLK caller
specified
> F_RDLCKP or F_WRLCKP, might it make sense to report the l_type on the
> conflicting lock as F_RDLCKP or F_WRLCKP if that conflicting lock is also
a *P
> type?
> 
> ...or maybe we should consider a new F_GETLKP cmd value, and a new
> expanded struct flock that gives more info. The pid is already somewhat
> meaningless with this sort of lock. Perhaps we could obfuscate the
fl_owner
> value and report that instead? What other sorts of info would be useful to
> programs that intend to use these new interfaces?

I always wonder if anyone actually uses the conflicting lock information...

I think returning the lock type as F_RDLCK or F_WRLCK is fine, but maybe an
extended F_GETLKP could report the extended type. For Ganesha, we wouldn't
use the extended type since the NFS protocol has no concept of separate
private and non-private locks (all NFS locks are "private" to the specified
owner in the request). The pid is also not that useful to Ganesha.

Frank

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