On Thu, Dec 06, 2007 at 09:51:30AM -0600, Serge E. Hallyn wrote:
> Quoting Vitaliy Gusev (vgusev@xxxxxxxxxx):
> > fl_pid is used by nfs, fuse and gfs2. For instance nfs keeps in fl_pid some
> > unique id to identify locking process between hosts - it is not a process
> > pid.
>
> Ok, but so the struct user_flock->fl_pid is being set to the task's
> virtual pid, while the struct kernel_flock->fl_pid is being set to
> task->tgid for nfsd use.
>
> Why can't nfs just generate a uniqueid from the struct pid when it
> needs it?
>
> Fuse just seems to copy the pid to report it to userspace, so it would
> just copy pid_vnr(kernel_flock->pid) into user_flock->fl_pid.
>
> Anyway I haven't looked at all the uses of struct fl_pid, but you
> can always get the pidnr back from the struct pid if needed so there
> should be no problem.
Perhaps we could add a sysid field like some unix systems have. Here
is the flock structure documentation from Sun:
----
The flock structure contains at least the following elements:
short l_type; /* lock operation type */
short l_whence; /* lock base indicator */
off_t l_start; /* starting offset from base */
off_t l_len; /* lock length; l_len == 0 means
until end of file */
int l_sysid; /* system ID running process holding lock */
pid_t l_pid; /* process ID of process holding lock */
----
Using the sysid could show that the pid field refers to a separate
namespace, and might also be useful for NFS to show that the lock
is really held by a process on a different system. This would also
be something we could export to user space in a way that some
programs are already written to expect and handle properly.
Brad Boyer
flar@xxxxxxxxxxxxx
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