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Add new example loadable kernel module: readhappy_mpsafe

readhappy_mpsafe - demonstrates how to make a module MPSAFE

This module contains an additional helper program test_readhappy.c,
that is designed to exercise the kernel module with multiple threads.

Submitted by <Siddharth Muralee>
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krytarowski committed Apr 20, 2018
1 parent 1daeffb commit c2427f654fd9fe2b9fcdf0ab1d91cbfe7cbc706c
@@ -1,14 +1,15 @@
# $NetBSD: Makefile,v 1.4 2018/04/13 20:30:09 kamil Exp $
# $NetBSD: Makefile,v 1.5 2018/04/20 00:06:45 kamil Exp $
.include <bsd.own.mk>
SUBDIR+= hello
SUBDIR+= executor
#SUBDIR+= luahello # Nothing to build here, only text files
SUBDIR+= luareadhappy # Needs an additional Lua script
SUBDIR+= ping # Needs an additional helper program
SUBDIR+= hello
#SUBDIR+= luahello # Nothing to build here, only text files
SUBDIR+= luareadhappy # Needs an additional Lua script
SUBDIR+= ping # Needs an additional helper program
SUBDIR+= properties
SUBDIR+= readhappy
SUBDIR+= readhappy_mpsafe # Contains an additional helper program
SUBDIR+= sysctl
.include <bsd.subdir.mk>
@@ -1,4 +1,4 @@
$NetBSD: README,v 1.6 2018/04/13 20:30:09 kamil Exp $
$NetBSD: README,v 1.7 2018/04/20 00:06:45 kamil Exp $
Kernel Developer's Manual
@@ -13,6 +13,7 @@ DESCRIPTION
* properties - handle incoming properties during the module load
* ping - basic ioctl(9)
* readhappy - basic implementation of read(9) with happy numbers
* readhappy_mpsafe- demonstrates how to make a module MPSAFE
* sysctl - demonstrates adding a sysctl handle dynamically
To build the examples you need a local copy of NetBSD sources. You also
@@ -58,8 +59,8 @@ HISTORY
ping, luahello and luareadhappy) first appeared in NetBSD 8.0; they were
written by Kamil Rytarowski.
The executor and sysctls module first appeared in NetBSD 9.0 and were
authored by Siddharth Muralee.
The readhappy_mpsafe, executor and sysctls modules first appeared in NetBSD
9.0 and were authored by Siddharth Muralee.
AUTHORS
This document was written by Kamil Rytarowski.
@@ -0,0 +1,22 @@
# $NetBSD: Makefile,v 1.1 2018/04/20 00:06:45 kamil Exp $
.include "../Makefile.inc"
#S?= /usr/src/sys
KMOD= readhappy_mpsafe
SRCS= readhappy_mpsafe.c
.include <bsd.kmodule.mk>
# To make use of this module, you'll need to separately build the
# test_readhappy program, with a Makefile similar to
#
# MKMAN= NO
# PROG= test_readhappy
#
# CFLAGS+=-pthread
#
# LDADD+= -lpthread
# DPADD+= ${LIBPTHREAD}
#
# .include <bsd.prog.mk>
@@ -0,0 +1,243 @@
/* $NetBSD: readhappy_mpsafe.c,v 1.1 2018/04/20 00:06:45 kamil Exp $ */
/*-
* Copyright (c) 2018 The NetBSD Foundation, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: readhappy_mpsafe.c,v 1.1 2018/04/20 00:06:45 kamil Exp $");
#include <sys/param.h>
#include <sys/module.h>
#include <sys/condvar.h>
#include <sys/conf.h>
#include <sys/device.h>
#include <sys/kernel.h>
#include <sys/mutex.h>
/*
* This module is a modification of the readhappy module to illustrate
* how to make a device MPSAFE (Multiprocessor Safe).
*
* 1. Supports opening device by multiple processes but allows only one at a time.
* 2. Supports multiple read() functions but allows only one at a time.
* 3. Uses mutex for ensuring synchonization.
*
* Create a device /dev/happy_mpsafe from which you can read sequential happy numbers.
*
* To use this device you need to do:
* mknod /dev/happy_mpsafe c 210 0
*
* To test whether the device is MPSAFE. Compile and run the test_readhappy file
* provided.
*/
#define HAPPY_NUMBER 1
#define SAD_NUMBER 4
/*
* kmutex_t variables have been added to the structure to
* ensure proper synchronization while opened by multiple devices.
*
* kcondvar_t conditional variable added. Boolean part added to
* check whether the device is in use.
*/
struct happy_softc {
kcondvar_t cv;
bool inuse_cv;
unsigned last;
kmutex_t lock;
kmutex_t read_lock;
};
static struct happy_softc sc;
static unsigned
dsum(unsigned n)
{
unsigned sum, x;
for (sum = 0; n; n /= 10) {
x = n % 10;
sum += x * x;
}
return sum;
}
static int
check_happy(unsigned n)
{
unsigned total;
KASSERT(mutex_owned(&sc.read_lock));
for (;;) {
total = dsum(n);
if (total == HAPPY_NUMBER)
return 1;
if (total == SAD_NUMBER)
return 0;
n = total;
}
}
dev_type_open(happy_open);
dev_type_close(happy_close);
dev_type_read(happy_read);
/*
* Notice that the .d_flag has a additional D_MPSAFE flag to
* tag is as a multiprocessor safe device.
*/
static struct cdevsw happy_cdevsw = {
.d_open = happy_open,
.d_close = happy_close,
.d_read = happy_read,
.d_write = nowrite,
.d_ioctl = noioctl,
.d_stop = nostop,
.d_tty = notty,
.d_poll = nopoll,
.d_mmap = nommap,
.d_kqfilter = nokqfilter,
.d_discard = nodiscard,
.d_flag = D_OTHER | D_MPSAFE,
};
/*
* happy_open : used to open the device for read. mutex_enter and mutex_exit:
* to lock the critical section and allow only a single process to open the
* device at a time.
*/
int
happy_open(dev_t self __unused, int flag __unused, int mode __unused,
struct lwp *l __unused)
{
int error;
error = 0;
mutex_enter(&sc.lock);
while (sc.inuse_cv == true) {
error = cv_wait_sig(&sc.cv, &sc.lock);
if (error)
break;
}
if (!error) {
sc.inuse_cv = true;
sc.last = 0;
}
mutex_exit(&sc.lock);
return 0;
}
/*
* happy_close allows only a single process to close the device at a time.
* It uses mutex_enter and mutex_exit for the same.
*/
int
happy_close(dev_t self __unused, int flag __unused, int mode __unused,
struct lwp *l __unused)
{
mutex_enter(&sc.lock);
sc.inuse_cv = false;
cv_signal(&sc.cv);
mutex_exit(&sc.lock);
return 0;
}
/*
* happy_read allows only a single file descriptor to read at a point of time
* it uses mutex_enter and mutex_exit: to lock the critical section and allow
* only a single process to open the device at a time.
*/
int
happy_read(dev_t self __unused, struct uio *uio, int flags __unused)
{
char line[80];
int error, len;
mutex_enter(&sc.read_lock);
while (check_happy(++sc.last) == 0)
continue;
len = snprintf(line, sizeof(line), "%u\n", sc.last);
if (uio->uio_resid < len) {
--sc.last;
error = EINVAL;
goto fin;
}
error = uiomove(line, len, uio);
fin:
mutex_exit(&sc.read_lock);
return error;
}
MODULE(MODULE_CLASS_MISC, happy_mpsafe, NULL);
/*
* Initializing mutex and conditional variables for read() and open().
* when the module is being loaded.
*/
static int
happy_mpsafe_modcmd(modcmd_t cmd, void *arg __unused)
{
int cmajor = 210, bmajor = -1;
switch (cmd) {
case MODULE_CMD_INIT:
if (devsw_attach("happy_mpsafe", NULL, &bmajor, &happy_cdevsw,
&cmajor))
return ENXIO;
mutex_init(&sc.lock, MUTEX_DEFAULT, IPL_NONE);
mutex_init(&sc.read_lock, MUTEX_DEFAULT, IPL_NONE);
cv_init(&sc.cv, "example conditional variable");
return 0;
case MODULE_CMD_FINI:
mutex_destroy(&sc.lock);
mutex_destroy(&sc.read_lock);
cv_destroy(&sc.cv);
devsw_detach(NULL, &happy_cdevsw);
return 0;
default:
return ENOTTY;
}
}
@@ -0,0 +1,82 @@
/* $NetBSD: test_readhappy.c,v 1.1 2018/04/20 00:06:45 kamil Exp $ */
/*
* Copyright (c) 2018 The NetBSD Foundation, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
/*
* Compile this program with -pthread and run it to test the readhappy_mpsafe
* module. This program should print out happy numbers read from /dev/happy_mpsafe.
* Insert the module and make the /dev/happy_mpsafe node before executing this file.
*/
static void* read_happy(void *);
static FILE *fp;
/*
* thread function used to read /dev/happy_mpsafe and print them out.
*/
static void *
read_happy(void *unused)
{
int line;
for (;;) {
fscanf(fp, "%d", &line);
printf("%d\n", line);
fflush(stdout);
}
/* NOTREACHED */
return NULL;
}
/*
* main function : opens /dev/happy_mpsafe and sets the global file descriptor
* creates 100 threads which try to use the file descriptor to read
* from /dev/happy_mpsafe.
* This function does not return anything and will run in an infinite loop.
*/
int
main(int argc, const char *argv[])
{
pthread_t thr[100];
fp = fopen("/dev/happy_mpsafe","r");
if (fp == NULL)
err(EXIT_FAILURE, "open");
for (int i = 0; i < 100; i++)
pthread_create(&thr[i], NULL, read_happy, NULL);
(void)read_happy(NULL);
/* NOTREACHED */
return EXIT_SUCCESS;
}

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