linux-kernel - [RFC] PPS: Implementing LinuxPPS API with new syscalls

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Date:	Tue, 5 Jun 2007 09:25:01 +0200
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	linux-kernel@...r.kernel.org
Cc:	linuxpps@...enneenne.com, akpm@...ux-foundation.org
Subject: [RFC] PPS: Implementing LinuxPPS API with new syscalls

Hello,

after a little studing on new generic netlink interface and some
letters with Andrew Morton I decided to drop using the netlink API at
all and start using new specific syscalls.

Looking at current LinuxPPS API and at RFC2783 I think we need the
following syscalls:

   asmlinkage long sys_time_pps_find(int cmd, int __user *source,
                                          char __user *name, int namelen,
                                          char __user *path, int pathlen);
   asmlinkage long sys_time_pps_getparams(int source,
                                          struct pps_params __user *params);
   asmlinkage long sys_time_pps_setparams(int source,
                                          const struct pps_params __user *params);
   asmlinkage long sys_time_pps_getcap(int source, int __user *mode);
   asmlinkage long sys_time_pps_fetch(int source, const int tsformat,
                                          struct pps_info __user *info,
                                          const struct timespec __user *timeout);

In fact:

* the two LinuxPPS functions time_pps_findsource() and
time_pps_findpath() can be implemented with sys_time_pps_find()
specifying proper finding command into "cmd",

* the RFC2783 time_pps_create() and time_pps_destroy() are not needed
since no PPS sources are created or destryed from userspace. The former
can be simply implemented as follow:

   static int time_pps_create(int source, pps_handle_t *handle)
   {
           /* In LinuxPPS there are no differences between a PPS source and
            * a PPS handle so we return the same value. */
           *handle = source;

           return 0;
   }

while the latter is just a "return 0".

* the RFC2783 time_pps_kcbind() is not implemented into Linux so it is
just a "return -EOPNOTSUPP".

Also using syscalls the problem regarding the pps_handle_t type
disappears, even if the needed of using time_pps_findsource() or
time_pps_findpath() still remains.

Regarding the file timepps.h I think I should reintroduce it into the
kernel header files since it's needed to define new PPS types and new
syscalls wrappers for RFC2783 compatibility.

Comments? Suggestions? :)

Thanks a lot,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti@...eenne.com
Linux Device Driver                             giometti@...dd.com
Embedded Systems                     		giometti@...ux.it
UNIX programming                     phone:     +39 349 2432127
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