/*
 * Copyright IBM Corp. 2004,2007
 * Interface implementation for communication with the z/VM control program
 * Author(s): Christian Borntraeger <borntraeger@de.ibm.com>
 *
 *
 * z/VMs CP offers the possibility to issue commands via the diagnose code 8
 * this driver implements a character device that issues these commands and
 * returns the answer of CP.

 * The idea of this driver is based on cpint from Neale Ferguson and #CP in CMS
 */

#define KMSG_COMPONENT "vmcp"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <asm/cpcmd.h>
#include <asm/debug.h>
#include <asm/uaccess.h>
#include "vmcp.h"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Christian Borntraeger <borntraeger@de.ibm.com>");
MODULE_DESCRIPTION("z/VM CP interface");

static debug_info_t *vmcp_debug;

static int vmcp_open(struct inode *inode, struct file *file)
{
        struct vmcp_session *session;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        session = kmalloc(sizeof(*session), GFP_KERNEL);
        if (!session)
                return -ENOMEM;

        session->bufsize = PAGE_SIZE;
        session->response = NULL;
        session->resp_size = 0;
        mutex_init(&session->mutex);
        file->private_data = session;
        return nonseekable_open(inode, file);
}

static int vmcp_release(struct inode *inode, struct file *file)
{
        struct vmcp_session *session;

        session = (struct vmcp_session *)file->private_data;
        file->private_data = NULL;
        free_pages((unsigned long)session->response, get_order(session->bufsize));
        kfree(session);
        return 0;
}

static ssize_t
vmcp_read(struct file *file, char __user *buff, size_t count, loff_t *ppos)
{
        ssize_t ret;
        size_t size;
        struct vmcp_session *session;

        session = file->private_data;
        if (mutex_lock_interruptible(&session->mutex))
                return -ERESTARTSYS;
        if (!session->response) {
                mutex_unlock(&session->mutex);
                return 0;
        }
        size = min_t(size_t, session->resp_size, session->bufsize);
        ret = simple_read_from_buffer(buff, count, ppos,
                                        session->response, size);

        mutex_unlock(&session->mutex);

        return ret;
}

static ssize_t
vmcp_write(struct file *file, const char __user *buff, size_t count,
           loff_t *ppos)
{
        char *cmd;
        struct vmcp_session *session;

        if (count > 240)
                return -EINVAL;
        cmd = kmalloc(count + 1, GFP_KERNEL);
        if (!cmd)
                return -ENOMEM;
        if (copy_from_user(cmd, buff, count)) {
                kfree(cmd);
                return -EFAULT;
        }
        cmd[count] = '\0';
        session = (struct vmcp_session *)file->private_data;
        if (mutex_lock_interruptible(&session->mutex)) {
                kfree(cmd);
                return -ERESTARTSYS;
        }
        if (!session->response)
                session->response = (char *)__get_free_pages(GFP_KERNEL
                                                | __GFP_REPEAT | GFP_DMA,
                                                get_order(session->bufsize));
        if (!session->response) {
                mutex_unlock(&session->mutex);
                kfree(cmd);
                return -ENOMEM;
        }
        debug_text_event(vmcp_debug, 1, cmd);
        session->resp_size = cpcmd(cmd, session->response, session->bufsize,
                                   &session->resp_code);
        mutex_unlock(&session->mutex);
        kfree(cmd);
        *ppos = 0;              /* reset the file pointer after a command */
        return count;
}


/*
 * These ioctls are available, as the semantics of the diagnose 8 call
 * does not fit very well into a Linux call. Diagnose X'08' is described in
 * CP Programming Services SC24-6084-00
 *
 * VMCP_GETCODE: gives the CP return code back to user space
 * VMCP_SETBUF: sets the response buffer for the next write call. diagnose 8
 * expects adjacent pages in real storage and to make matters worse, we
 * dont know the size of the response. Therefore we default to PAGESIZE and
 * let userspace to change the response size, if userspace expects a bigger
 * response
 */
static long vmcp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct vmcp_session *session;
        int temp;

        session = (struct vmcp_session *)file->private_data;
        if (mutex_lock_interruptible(&session->mutex))
                return -ERESTARTSYS;
        switch (cmd) {
        case VMCP_GETCODE:
                temp = session->resp_code;
                mutex_unlock(&session->mutex);
                return put_user(temp, (int __user *)arg);
        case VMCP_SETBUF:
                free_pages((unsigned long)session->response,
                                get_order(session->bufsize));
                session->response=NULL;
                temp = get_user(session->bufsize, (int __user *)arg);
                if (get_order(session->bufsize) > 8) {
                        session->bufsize = PAGE_SIZE;
                        temp = -EINVAL;
                }
                mutex_unlock(&session->mutex);
                return temp;
        case VMCP_GETSIZE:
                temp = session->resp_size;
                mutex_unlock(&session->mutex);
                return put_user(temp, (int __user *)arg);
        default:
                mutex_unlock(&session->mutex);
                return -ENOIOCTLCMD;
        }
}

static const struct file_operations vmcp_fops = {
        .owner          = THIS_MODULE,
        .open           = vmcp_open,
        .release        = vmcp_release,
        .read           = vmcp_read,
        .write          = vmcp_write,
        .unlocked_ioctl = vmcp_ioctl,
        .compat_ioctl   = vmcp_ioctl,
};

static struct miscdevice vmcp_dev = {
        .name   = "vmcp",
        .minor  = MISC_DYNAMIC_MINOR,
        .fops   = &vmcp_fops,
};

static int __init vmcp_init(void)
{
        int ret;

        if (!MACHINE_IS_VM) {
                pr_warning("The z/VM CP interface device driver cannot be "
                           "loaded without z/VM\n");
                return -ENODEV;
        }

        vmcp_debug = debug_register("vmcp", 1, 1, 240);
        if (!vmcp_debug)
                return -ENOMEM;

        ret = debug_register_view(vmcp_debug, &debug_hex_ascii_view);
        if (ret) {
                debug_unregister(vmcp_debug);
                return ret;
        }

        ret = misc_register(&vmcp_dev);
        if (ret) {
                debug_unregister(vmcp_debug);
                return ret;
        }

        return 0;
}

static void __exit vmcp_exit(void)
{
        misc_deregister(&vmcp_dev);
        debug_unregister(vmcp_debug);
}

module_init(vmcp_init);
module_exit(vmcp_exit);