[PATCH] posix message queues: implementation

From: Manfred Spraul <manfred@colorfullife.com>

Actual implementation of the posix message queues, written by Krzysztof
Benedyczak and Michal Wronski.  The complete implementation is dependant on
CONFIG_POSIX_MQUEUE.

It passed the openposix test suite with two exceptions: one mq_unlink test
was bad and tested undefined behavior.  And Linux succeeds
mq_close(open(,,,)).  The spec mandates EBADF, but we have decided to ignore
that: we would have to add a new syscall just for the right error code.

The patch intentionally doesn't use all helpers from fs/libfs for kernel-only
filesystems: step 5 allows user space mounts of the file system.



Signal changes:

The patch redefines SI_MESGQ using __SI_CODE: The generic Linux ABI uses
a negative value (i.e.  from user) for SI_MESGQ, but the kernel internal
value must be posive to pass check_kill_value.  Additionally, the patch
adds support into copy_siginfo_to_user to copy the "new" signal type to
user space.



Changes in signal code caused by POSIX message queues patch:

General & rationale:

  mqueues generated signals (only upon notification) must have si_code
  == SI_MESGQ.  In fact such a signal is send from one process which
  caused notification (== sent message to empty message queue) to
  another which requested it.  Both processes can be of course unrelated
  in terms of uids/euids.  So SI_MESGQ signals must be classified as
  SI_FROMKERNEL to pass check_kill_permissions (not need to say that
  this signals ARE from kernel).

  Signals generated by message queues notification need the same
  fields in siginfo struct's union _sifields as POSIX.1b signals and we
  can reuse its union entry.

  SI_MESGQ was previously defined to -3 in kernel and also in glibc. 
  So in userspace SI_MESGQ must be still visible as -3.

Solution:

  SI_MESGQ is defined in the same style as SI_TIMER using __SI_CODE macro.

  Details:

    Fortunately copy_siginfo_to_user copies si_code as short.  So we
    can use remaining part of int value freely.  __SI_CODE does the
    work.  SI_MESGQ is in kernel:

 		6<<16 | (-3 & 0xffff) what is > 0

    but to userspace is copied

 		(short) SI_MESGQ == -3

Actual changes:

  Changes in include/asm-generic/siginfo.h

  __SI_MESGQ added in signal.h to represent inside-kernel prefix of
  SI_MESGQ.  SI_MESGQ is redefined from -3 to __SI_CODE(__SI_MESGQ, -3)

  Except mips architecture those changes should be arch independent
  (asm-generic/siginfo.h is included in arch versions).  On mips
  SI_MESGQ is redefined to -4 in order to be compatible with IRIX.  But
  the same schema can be used.

  Change in copy_siginfo_to_user: We only add one line to order the
  same copy semantics as for _SI_RT.

  This change isn't very portable - some arch have its own
  copy_siginfo_to_user.  All those should have similar change (but
  possibly not one-line as _SI_RT case was sometimes ignored because i
  wasn't used yet, e.g.  see ia64 signal.c).

Update:
mq: only fail with invalid timespec if mq_timed{send,receive} needs to block
From: Jakub Jelinek <jakub@redhat.com>

POSIX requires EINVAL to be set if:
"The process or thread would have blocked, and the abs_timeout parameter
specified a nanoseconds field value less than zero or greater than or equal
to 1000 million."
but 2.6.5-mm3 returns -EINVAL even if the process or thread would not block
(if the queue is not empty for timedreceive or not full for timedsend).

CREDITS

@@ -289,6 +289,15 @@ S: Via Delle Palme, 9
 S: Terni 05100
 S: Italy
 
+N: Krzysztof Benedyczak
+E: golbi@mat.uni.torun.pl
+W: http://www.mat.uni.torun.pl/~golbi
+D: POSIX message queues fs (with M. Wronski)
+S: ul. Podmiejska 52
+S: Radunica
+S: 83-000 Pruszcz Gdanski
+S: Poland
+
 N: Randolph Bentson
 E: bentson@grieg.seaslug.org
 W: http://www.aa.net/~bentson/
@@ -3485,6 +3494,14 @@ S: 12725 SW Millikan Way, Suite 400
 S: Beaverton, OR 97005
 S: USA
 
+N: Michal Wronski
+E: wrona@mat.uni.torun.pl
+W: http://www.mat.uni.torun.pl/~wrona
+D: POSIX message queues fs (with K. Benedyczak)
+S: ul. Teczowa 23/12
+S: 80-680 Gdansk-Sobieszewo
+S: Poland
+
 N: Frank Xia
 E: qx@math.columbia.edu
 D: Xiafs filesystem [defunct]

Documentation/filesystems/proc.txt

@@ -38,6 +38,7 @@ Table of Contents
   2.8	/proc/sys/net/ipv4 - IPV4 settings
   2.9	Appletalk
   2.10	IPX
+  2.11	/proc/sys/fs/mqueue - POSIX message queues filesystem
 
 ------------------------------------------------------------------------------
 Preface
@@ -1814,6 +1815,30 @@ The /proc/net/ipx_route  table  holds  a list of IPX routes. For each route it
 gives the  destination  network, the router node (or Directly) and the network
 address of the router (or Connected) for internal networks.
 
+2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
+----------------------------------------------------------
+
+The "mqueue"  filesystem provides  the necessary kernel features to enable the
+creation of a  user space  library that  implements  the  POSIX message queues
+API (as noted by the  MSG tag in the  POSIX 1003.1-2001 version  of the System
+Interfaces specification.)
+
+The "mqueue" filesystem contains values for determining/setting  the amount of
+resources used by the file system.
+
+/proc/sys/fs/mqueue/queues_max is a read/write  file for  setting/getting  the
+maximum number of message queues allowed on the system.
+
+/proc/sys/fs/mqueue/msg_max  is  a  read/write file  for  setting/getting  the
+maximum number of messages in a queue value.  In fact it is the limiting value
+for another (user) limit which is set in mq_open invocation. This attribute of
+a queue must be less or equal then msg_max.
+
+/proc/sys/fs/mqueue/msgsize_max is  a read/write  file for setting/getting the
+maximum  message size value (it is every  message queue's attribute set during
+its creation).
+
+
 ------------------------------------------------------------------------------
 Summary
 ------------------------------------------------------------------------------

include/asm-generic/siginfo.h

@@ -123,6 +123,7 @@ typedef struct siginfo {
 #define __SI_FAULT	(3 << 16)
 #define __SI_CHLD	(4 << 16)
 #define __SI_RT		(5 << 16)
+#define __SI_MESGQ	(6 << 16)
 #define __SI_CODE(T,N)	((T) | ((N) & 0xffff))
 #else
 #define __SI_KILL	0
@@ -131,6 +132,7 @@ typedef struct siginfo {
 #define __SI_FAULT	0
 #define __SI_CHLD	0
 #define __SI_RT		0
+#define __SI_MESGQ	0
 #define __SI_CODE(T,N)	(N)
 #endif
 
@@ -142,7 +144,7 @@ typedef struct siginfo {
 #define SI_KERNEL	0x80		/* sent by the kernel from somewhere */
 #define SI_QUEUE	-1		/* sent by sigqueue */
 #define SI_TIMER __SI_CODE(__SI_TIMER,-2) /* sent by timer expiration */
-#define SI_MESGQ	-3		/* sent by real time mesq state change */
+#define SI_MESGQ __SI_CODE(__SI_MESGQ,-3) /* sent by real time mesq state change */
 #define SI_ASYNCIO	-4		/* sent by AIO completion */
 #define SI_SIGIO	-5		/* sent by queued SIGIO */
 #define SI_TKILL	-6		/* sent by tkill system call */

init/Kconfig

@@ -90,6 +90,24 @@ config SYSVIPC
 	  section 6.4 of the Linux Programmer's Guide, available from
 	  <http://www.tldp.org/guides.html>.
 
+config POSIX_MQUEUE
+	bool "POSIX Message Queues"
+	depends on EXPERIMENTAL
+	---help---
+	  POSIX variant of message queues is a part of IPC. In POSIX message
+	  queues every message has a priority which decides about succession
+	  of receiving it by a process. If you want to compile and run
+	  programs written e.g. for Solaris with use of its POSIX message
+	  queues (functions mq_*) say Y here. To use this feature you will
+	  also need mqueue library, available from
+	  <http://www.mat.uni.torun.pl/~wrona/posix_ipc/>
+
+	  POSIX message queues are visible as a filesystem called 'mqueue'
+	  and can be mounted somewhere if you want to do filesystem
+	  operations on message queues.
+
+	  If unsure, say Y.
+
 config BSD_PROCESS_ACCT
 	bool "BSD Process Accounting"
 	help

ipc/Makefile

@@ -4,3 +4,5 @@
 
 obj-$(CONFIG_SYSVIPC_COMPAT) += compat.o
 obj-$(CONFIG_SYSVIPC) += util.o msgutil.o msg.o sem.o shm.o
+obj-$(CONFIG_POSIX_MQUEUE) += mqueue.o msgutil.o
+

kernel/signal.c

@@ -2047,6 +2047,7 @@ int copy_siginfo_to_user(siginfo_t __user *to, siginfo_t *from)
 		err |= __put_user(from->si_stime, &to->si_stime);
 		break;
 	case __SI_RT: /* This is not generated by the kernel as of now. */
+	case __SI_MESGQ: /* But this is */
 		err |= __put_user(from->si_pid, &to->si_pid);
 		err |= __put_user(from->si_uid, &to->si_uid);
 		err |= __put_user(from->si_int, &to->si_int);