vmcp.c

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/*
 * Copyright IBM Corp. 2004, 2010
 * Interface implementation for communication with the z/VM control program
 *
 * Author(s): Christian Borntraeger <[email protected]>
 *
 * 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
 */

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

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 = 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 = 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 __user *argp;
    int temp;

    session = file->private_data;
    if (is_compat_task())
        argp = compat_ptr(arg);
    else
        argp = (int __user *)arg;
    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, argp);
    case VMCP_SETBUF:
        free_pages((unsigned long)session->response,
                get_order(session->bufsize));
        session->response=NULL;
        temp = get_user(session->bufsize, argp);
        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, argp);
    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,
    .llseek     = no_llseek,
};

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)
        return 0;

    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;
}
device_initcall(vmcp_init);