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.
>
> 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
>
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