Fix cdev kld example after it has been broken for year or so. Also extend list

of supported operations by example read() and write() operations.

Inspired by:    http://www.daemonnews.org/200010/blueprints.html
PR:             16173
Submitted by:   sobomax

share/examples/kld/cdev/README

@@ -58,6 +58,8 @@
 # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 # SUCH DAMAGE.
 #
+# $FreeBSD$
+#
 
 1.0	Overview
 
@@ -83,6 +85,19 @@
 	try out changes to kernel code without rebuilding and
 	booting from the new kernel.
 
+	The idea behind this example is to show some interaction
+	with the device driver. Therefore the flow of the code that
+	this driver is aimed at is as follows:
+
+	    open(2) -> ioctl(2) -> write(2) -> read(2) -> close(2).
+
+	We will first open the device in the /dev/ directory; then
+	we will send an ioctl message to it using ioctl(2) call;
+	then write a small string via the write(2) call. This string
+	we write to the device will be stored in a static buffer,
+	and later will be accessible via the read(2) call. Finally,
+	we will close(2) our open()'d device so that we may no
+	longer make read or write calls on it.
 
 2.0	Directions
 

share/examples/kld/cdev/module/Makefile

@@ -78,8 +78,8 @@ KLDUNLOAD	= /sbin/kldunload
 
 CLEANFILES+= ${KMOD}
 
-load: /dev/cdev
-	${KLDLOAD} -v ./${KMOD}
+load: /dev/cdev ${KMOD}.ko
+	${KLDLOAD} -v ./${KMOD}.ko
 
 unload:
 	rm -f /dev/cdev

share/examples/kld/cdev/module/cdev.c

@@ -64,7 +64,11 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
+ *
+ * $FreeBSD$
  */
+#include <sys/types.h>
+#include <sys/uio.h>
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/ioccom.h>
@@ -90,11 +94,17 @@
 
 #define CDEV_IOCTL1         _IOR('C', 1, u_int)
 
+/* Stores string recv'd by _write() */
+static char buf[512+1];
+static int len;
+
 int
 mydev_open(dev_t dev, int flag, int otyp, struct proc *procp)
 {
     printf("mydev_open: dev_t=%d, flag=%x, otyp=%x, procp=%p\n",
 	   dev2udev(dev), flag, otyp, procp);
+    memset(&buf, '\0', 513);
+    len = 0;
     return (0);
 }
 
@@ -125,3 +135,43 @@ mydev_ioctl(dev_t dev, u_long cmd, caddr_t arg, int mode, struct proc *procp)
     }
     return error;
 }
+
+/*
+ * mydev_write takes in a character string and saves it
+ * to buf for later accessing.
+ */
+int
+mydev_write(dev_t dev, struct uio *uio, int ioflag)
+{
+    int err = 0;
+
+    printf("mydev_write: dev_t=%d, uio=%p, ioflag=%d\n",
+	dev2udev(dev), uio, ioflag);
+
+    err = copyinstr(uio->uio_iov->iov_base, &buf, 512, &len);
+    if (err != 0) {
+	printf("Write to \"cdev\" failed.\n");
+    }
+    return(err);
+}
+
+/*
+ * The mydev_read function just takes the buf that was saved 
+ * via mydev_write() and returns it to userland for
+ * accessing.
+ */
+int
+mydev_read(dev_t dev, struct uio *uio, int ioflag)
+{
+    int err = 0;
+
+    printf("mydev_read: dev_t=%d, uio=%p, ioflag=%d\n",
+	dev2udev(dev), uio, ioflag);
+
+    if (len <= 0) {
+	err = -1; 
+    } else {	/* copy buf to userland */
+	copystr(&buf, uio->uio_iov->iov_base, 513, &len);
+    }
+    return(err);
+}

share/examples/kld/cdev/module/cdev.h

@@ -65,13 +65,17 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
+ *
+ * $FreeBSD$
  */
 
 #ifndef __CDEV_H_
 #define __CDEV_H_
 
-d_open_t mydev_open;
-d_close_t mydev_close;
-d_ioctl_t mydev_ioctl;
+d_open_t	mydev_open;
+d_close_t	mydev_close;
+d_ioctl_t	mydev_ioctl;
+d_read_t	mydev_read;
+d_write_t	mydev_write;
 
 #endif 

share/examples/kld/cdev/module/cdevmod.c

@@ -64,6 +64,8 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
+ *
+ * $FreeBSD$
  */
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -78,25 +80,27 @@
 static struct cdevsw my_devsw = {
 	/* open */	mydev_open,
 	/* close */	mydev_close,
-	/* read */	noread,
-	/* write */	nowrite,
+	/* read */	mydev_read,
+	/* write */	mydev_write,
 	/* ioctl */	mydev_ioctl,
-	/* stop */	nostop,
-	/* reset */	noreset,
-	/* devtotty */	nodevtotty,
 	/* poll */	nopoll,
 	/* mmap */	nommap,
 	/* strategy */	nostrategy,
 	/* name */	"cdev",
-	/* parms */	noparms,
 	/* maj */	CDEV_MAJOR,
 	/* dump */	nodump,
 	/* psize */	nopsize,
 	/* flags */	D_TTY,
-	/* maxio */	0,
 	/* bmaj */	-1
 };
 
+/* 
+ * Used as the variable that is the reference to our device
+ * in devfs... we must keep this variable sane until we 
+ * call kldunload.
+ */
+static dev_t sdev;
+
 /*
  * This function is called each time the module is loaded or unloaded.
  * Since we are a miscellaneous module, we have to provide whatever
@@ -123,10 +127,12 @@ cdev_load(module_t mod, int cmd, void *arg)
 	printf("Copyright (c) 1998\n");
 	printf("Rajesh Vaidheeswarran\n");
 	printf("All rights reserved\n");
+	sdev = make_dev(&my_devsw, 0, UID_ROOT, GID_WHEEL, 0600, "cdev");
 	break;		/* Success*/
 
     case MOD_UNLOAD:
 	printf("Unloaded kld character device driver\n");
+	destroy_dev(sdev);
 	break;		/* Success*/
 
     default:	/* we only understand load/unload*/
@@ -139,4 +145,4 @@ cdev_load(module_t mod, int cmd, void *arg)
 
 /* Now declare the module to the system */
 
-DEV_MODULE(cdev, CDEV_MAJOR, -1, my_devsw, cdev_load, 0);
+DEV_MODULE(cdev, cdev_load, NULL);

share/examples/kld/cdev/test/Makefile

@@ -87,6 +87,6 @@ unload:
 	@echo "has been successfully unloaded by building 'unload' in"
 	@echo "the 'module' subdirectory."
 	@echo
-	${MODSTAT} -n misc_mod
+	${MODSTAT} -n cdev
 
 .include <bsd.prog.mk>

share/examples/kld/cdev/test/testcdev.c

@@ -67,21 +67,28 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
+ *
+ * $FreeBSD$
  */
 #include <stdio.h>
 #include <fcntl.h>
+#include <string.h>
 #include <sys/ioccom.h>
 
 #define CDEV_IOCTL1     _IOR('C', 1, u_int)
 #define CDEV_DEVICE	"cdev"
 
+static char writestr[] = "Hello kernel!";
+static char buf[512+1];
+
 int
 main(int argc, char *argv[])
 {
     int kernel_fd;
     int one;
+    int len;
 
-    if ((kernel_fd = open("/dev/" CDEV_DEVICE, O_RDONLY)) == -1) {
+    if ((kernel_fd = open("/dev/" CDEV_DEVICE, O_RDWR)) == -1) {
 	perror("/dev/" CDEV_DEVICE);
 	exit(1);
     }
@@ -92,5 +99,22 @@ main(int argc, char *argv[])
     } else {
 	printf( "Sent ioctl CDEV_IOCTL1 to device /dev/" CDEV_DEVICE "\n");
     }
+
+    len = strlen(writestr) + 1;
+
+    /* Write operation */
+    if (write(kernel_fd, writestr, len) == -1) {
+	perror("write()");
+    } else {
+	printf("Written \"%s\" string to device /dev/" CDEV_DEVICE "\n", writestr);
+    }
+
+    /* Read operation */
+    if (read(kernel_fd, buf, len) == -1) {
+	perror("read()");
+    } else {
+	printf("Read \"%s\" string from device /dev/" CDEV_DEVICE "\n", buf);
+    }
+
     exit(0);
 }