On Tue, 4 Mar 2014 14:22:12 -0500
"J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> On Tue, Mar 04, 2014 at 02:09:08PM -0500, Jeff Layton wrote:
> > Neil Brown suggested potentially overloading the l_pid value as a "lock
> > context" field for file-private locks. While I don't think we will
> > probably want to do that here, it's probably a good idea to ensure that
> > in the future we could extend this API without breaking existing
> > callers.
> >
> > Typically the l_pid value is ignored for incoming struct flock
> > arguments, serving mainly as a place to return the pid of the owner if
> > there is a conflicting lock. For file-private locks, require that it
> > currently be set to 0 and return EINVAL if it isn't. If we eventually
> > want to make a non-zero l_pid mean something, then this will help ensure
> > that we don't break legacy programs that are using file-private locks.
>
> Makes sense to me.
>
> But, could you add move most of this initialization to a helper
> function? Or, better, just add it to flock64_to_posix_lock? That would
> a) remove some code duplication, and b) give a single place to add a
> comment documenting the above rationale for the new check.
>
> --b.
>
Well we could consolidate it, but I don't think it'll make the patch
any smaller. We could add this to flock_to_posix_lock but you'd need to
know whether this is for a classic or file-private lock. We can't
reasonably enforce the l_pid == 0 requirement in the classic case.
So, we could do that but we'd have to start passing flock_to_posix_lock
the cmd value or a flag or something...
> >
> > Cc: Neil Brown <neilb@xxxxxxx>
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > fs/locks.c | 24 ++++++++++++++++++++++++
> > 1 file changed, 24 insertions(+)
> >
> > diff --git a/fs/locks.c b/fs/locks.c
> > index ce93815b0626..6fdf26a79cc8 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -1931,6 +1931,10 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock __user *l)
> > goto out;
> >
> > if (cmd == F_GETLKP) {
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_GETLK;
> > file_lock.fl_flags |= FL_FILE_PVT;
> > file_lock.fl_owner = (fl_owner_t)filp;
> > @@ -2062,11 +2066,19 @@ again:
> > */
> > switch (cmd) {
> > case F_SETLKP:
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_SETLK;
> > file_lock->fl_flags |= FL_FILE_PVT;
> > file_lock->fl_owner = (fl_owner_t)filp;
> > break;
> > case F_SETLKPW:
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_SETLKW;
> > file_lock->fl_flags |= FL_FILE_PVT;
> > file_lock->fl_owner = (fl_owner_t)filp;
> > @@ -2121,6 +2133,10 @@ int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 __user *l)
> > goto out;
> >
> > if (cmd == F_GETLKP) {
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_GETLK64;
> > file_lock.fl_flags |= FL_FILE_PVT;
> > file_lock.fl_owner = (fl_owner_t)filp;
> > @@ -2185,11 +2201,19 @@ again:
> > */
> > switch (cmd) {
> > case F_SETLKP:
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_SETLK64;
> > file_lock->fl_flags |= FL_FILE_PVT;
> > file_lock->fl_owner = (fl_owner_t)filp;
> > break;
> > case F_SETLKPW:
> > + error = -EINVAL;
> > + if (flock.l_pid != 0)
> > + goto out;
> > +
> > cmd = F_SETLKW64;
> > file_lock->fl_flags |= FL_FILE_PVT;
> > file_lock->fl_owner = (fl_owner_t)filp;
> > --
> > 1.8.5.3
> >
--
Jeff Layton <jlayton@xxxxxxxxxx>
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