Hi all,

I want a virtual sound driver that shall be used by the system for audio playback and capture. This driver shall read from a buffer and write to another buffer. So I have written the following very simple kernel module

Code:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sound.h>

#include <linux/sysctl.h>
#include <linux/device.h>

#include <linux/slab.h> /* kmalloc() */
#include <linux/gfp.h>
#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/pci.h>
#include <linux/err.h>

#include <sound/core.h>

static char* mod_name = "prosip";

MODULE_LICENSE("GPL");
MODULE_VERSION("0.0.1111");
MODULE_AUTHOR("Khaled Mahmood");
MODULE_DESCRIPTION("proSip Virtual Sound Card");

//
static int ver_major = 133;

static int ver_minor = 3;

//
static int buffer_size = 0;
static char* buffer;
static int read_count = 0;

/* Declaration of memory.c functions */
int prosip_open(struct inode *inode, struct file *filp);
int prosip_release(struct inode *inode, struct file *filp);

//
ssize_t prosip_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t prosip_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos);

//
int prosip_ioctl(struct inode *inode,struct file *file,unsigned int ioctl_num,unsigned long ioctl_param);

//
static int  __init prosip_init(void);
static void __exit prosip_exit(void);

/* Structure that declares the usual file access functions */
struct file_operations sound_fops =
{
owner:
    THIS_MODULE,
read:
    prosip_read,
write:
    prosip_write,
open:
    prosip_open,
release:
    prosip_release,
ioctl:
    prosip_ioctl
};


/* Declaration of the init and exit functions */
module_init(prosip_init);
module_exit(prosip_exit);

static int __init prosip_init(void)
{
    int ret = -1;
    buffer_size = 0;

    printk("<1>[prosip] Init...!\n");

    ret = register_sound_dsp(&sound_fops, ver_minor);

    if(ret < 0)
    {
        printk("<1> [prosip] Registration failure\n");
        //
        return ret;
    }
    else
    {
        ver_minor = ret;
        //
        printk("<1> [prosip] DSP Registered succesfully with id %d\n", ret);
    }

    buffer = kmalloc(101, GFP_KERNEL);

    if(buffer == 0)
    {
        printk("<1>[prosip] Failed to allocate buffer !!!\n");
        //
        return -ENOMEM;
    }

    //
    return 0;
}

static void __exit prosip_exit(void)
{
    printk("<1> [prosip] Sound Exit...\n");

    unregister_sound_special(ver_minor);

    if(buffer)
    {
        kfree(buffer);
    }

}

/* Declaration of memory.c functions */
int prosip_open(struct inode *inode, struct file *filp)
{
    printk("<1> [prosip] Sound Open... \n");

    try_module_get(THIS_MODULE);

    return 0;
}

//
int prosip_release(struct inode *inode, struct file *filp)
{
    printk("<1> [MySound] Sound Release... \n");

    module_put(THIS_MODULE);

    return 0;
}

//
ssize_t prosip_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
    printk("<1> [prosip] Sound read...\n");
    printk("<1> [prosip] Writing Count: %d\n", count);

    if(buffer == 0)
    {
        printk("<1> NULL buffer!!! Unable to read");
        return 0;
    }

    //
    count =  buffer_size;

    if(read_count == 0)
    {
        read_count = buffer_size;
    }
    else
    {
        read_count = 0;
    }

    copy_to_user(buf, buffer, buffer_size);

    printk("<1> [prosip] Buffer: %s, buf: %s, Count: %d\n", buffer, buf, count);

    return read_count;
}

//
ssize_t prosip_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos)
{
    printk("<1> [prosip] Sound write...!\n");
    printk("<1> [prosip] Writing Count: %d\n", count);

    //
    if(buffer == 0)
    {
        printk("<1> NULL buffer!!! Unable to write");

        return 0;
    }

    copy_from_user(buffer, buf, count);

    buffer[count] = 0;
    buffer_size = count;

    printk("<1> [MySound] Writing Buffer: %s, Count: %d\n", buffer, count);

    return count;
}

/*
* This function is called whenever a process tries to do an ioctl on our
* device file. 
*
*/
int prosip_ioctl(struct inode *inode,
                 struct file *file,
                 unsigned int ioctl_num,
                 unsigned long ioctl_param)
{
    //
    return 0;
}
insmoding the module creates a driver as /dev/dsp1. And I can read from and write to the device using cat and echo command.

Also I found the entry
Code:
/sys/devices/virtual/sound/dsp1
which make me believe it is inserted into the system as a virtual sound driver.

But how can I set this sound driver as a default driver of the system and let application use this driver for playback and capture audio.

I am using Ubuntu with kernel version 2.6.30-35 generic.

I am a newbie kernel developer and become stuck on how to solve the issue.

Thanks in advance
Khaled