// SPDX-License-Identifier: GPL-2.0
/*
 * Character device driver for reading z/VM *MONITOR service records.
 *
 * Copyright IBM Corp. 2004, 2009
 *
 * Author: Gerald Schaefer <gerald.schaefer@de.ibm.com>
 */

#define pr_fmt(fmt) "monreader: " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/ctype.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <net/iucv/iucv.h>
#include <linux/uaccess.h>
#include <asm/machine.h>
#include <asm/ebcdic.h>
#include <asm/extmem.h>


#define MON_COLLECT_SAMPLE 0x80
#define MON_COLLECT_EVENT  0x40
#define MON_SERVICE        "*MONITOR"
#define MON_IN_USE         0x01
#define MON_MSGLIM         255

static char mon_dcss_name[9] = "MONDCSS\0";

struct mon_msg {
        u32 pos;
        u32 mca_offset;
        struct iucv_message msg;
        char msglim_reached;
        char replied_msglim;
};

struct mon_private {
        struct iucv_path *path;
        struct mon_msg *msg_array[MON_MSGLIM];
        unsigned int   write_index;
        unsigned int   read_index;
        atomic_t msglim_count;
        atomic_t read_ready;
        atomic_t iucv_connected;
        atomic_t iucv_severed;
};

static unsigned long mon_in_use = 0;

static unsigned long mon_dcss_start;
static unsigned long mon_dcss_end;

static DECLARE_WAIT_QUEUE_HEAD(mon_read_wait_queue);
static DECLARE_WAIT_QUEUE_HEAD(mon_conn_wait_queue);

static u8 user_data_connect[16] = {
        /* Version code, must be 0x01 for shared mode */
        0x01,
        /* what to collect */
        MON_COLLECT_SAMPLE | MON_COLLECT_EVENT,
        /* DCSS name in EBCDIC, 8 bytes padded with blanks */
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
};

static u8 user_data_sever[16] = {
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
};

/******************************************************************************
 *                             helper functions                               *
 *****************************************************************************/
/*
 * Create the 8 bytes EBCDIC DCSS segment name from
 * an ASCII name, incl. padding
 */
static void dcss_mkname(char *ascii_name, char *ebcdic_name)
{
        int i;

        for (i = 0; i < 8; i++) {
                if (ascii_name[i] == '\0')
                        break;
                ebcdic_name[i] = toupper(ascii_name[i]);
        }
        for (; i < 8; i++)
                ebcdic_name[i] = ' ';
        ASCEBC(ebcdic_name, 8);
}

static inline unsigned long mon_mca_start(struct mon_msg *monmsg)
{
        return *(u32 *) &monmsg->msg.rmmsg;
}

static inline unsigned long mon_mca_end(struct mon_msg *monmsg)
{
        return *(u32 *) &monmsg->msg.rmmsg[4];
}

static inline u8 mon_mca_type(struct mon_msg *monmsg, u8 index)
{
        return *((u8 *)__va(mon_mca_start(monmsg)) + monmsg->mca_offset + index);
}

static inline u32 mon_mca_size(struct mon_msg *monmsg)
{
        return mon_mca_end(monmsg) - mon_mca_start(monmsg) + 1;
}

static inline u32 mon_rec_start(struct mon_msg *monmsg)
{
        return *((u32 *)(__va(mon_mca_start(monmsg)) + monmsg->mca_offset + 4));
}

static inline u32 mon_rec_end(struct mon_msg *monmsg)
{
        return *((u32 *)(__va(mon_mca_start(monmsg)) + monmsg->mca_offset + 8));
}

static int mon_check_mca(struct mon_msg *monmsg)
{
        if ((mon_rec_end(monmsg) <= mon_rec_start(monmsg)) ||
            (mon_rec_start(monmsg) < mon_dcss_start) ||
            (mon_rec_end(monmsg) > mon_dcss_end) ||
            (mon_mca_type(monmsg, 0) == 0) ||
            (mon_mca_size(monmsg) % 12 != 0) ||
            (mon_mca_end(monmsg) <= mon_mca_start(monmsg)) ||
            (mon_mca_end(monmsg) > mon_dcss_end) ||
            (mon_mca_start(monmsg) < mon_dcss_start) ||
            ((mon_mca_type(monmsg, 1) == 0) && (mon_mca_type(monmsg, 2) == 0)))
                return -EINVAL;
        return 0;
}

static int mon_send_reply(struct mon_msg *monmsg,
                          struct mon_private *monpriv)
{
        int rc;

        rc = iucv_message_reply(monpriv->path, &monmsg->msg,
                                IUCV_IPRMDATA, NULL, 0);
        atomic_dec(&monpriv->msglim_count);
        if (likely(!monmsg->msglim_reached)) {
                monmsg->pos = 0;
                monmsg->mca_offset = 0;
                monpriv->read_index = (monpriv->read_index + 1) %
                                      MON_MSGLIM;
                atomic_dec(&monpriv->read_ready);
        } else
                monmsg->replied_msglim = 1;
        if (rc) {
                pr_err("Reading monitor data failed with rc=%i\n", rc);
                return -EIO;
        }
        return 0;
}

static void mon_free_mem(struct mon_private *monpriv)
{
        int i;

        for (i = 0; i < MON_MSGLIM; i++)
                kfree(monpriv->msg_array[i]);
        kfree(monpriv);
}

static struct mon_private *mon_alloc_mem(void)
{
        int i;
        struct mon_private *monpriv;

        monpriv = kzalloc_obj(struct mon_private);
        if (!monpriv)
                return NULL;
        for (i = 0; i < MON_MSGLIM; i++) {
                monpriv->msg_array[i] = kzalloc_obj(struct mon_msg);
                if (!monpriv->msg_array[i]) {
                        mon_free_mem(monpriv);
                        return NULL;
                }
        }
        return monpriv;
}

static inline void mon_next_mca(struct mon_msg *monmsg)
{
        if (likely((mon_mca_size(monmsg) - monmsg->mca_offset) == 12))
                return;
        monmsg->mca_offset += 12;
        monmsg->pos = 0;
}

static struct mon_msg *mon_next_message(struct mon_private *monpriv)
{
        struct mon_msg *monmsg;

        if (!atomic_read(&monpriv->read_ready))
                return NULL;
        monmsg = monpriv->msg_array[monpriv->read_index];
        if (unlikely(monmsg->replied_msglim)) {
                monmsg->replied_msglim = 0;
                monmsg->msglim_reached = 0;
                monmsg->pos = 0;
                monmsg->mca_offset = 0;
                monpriv->read_index = (monpriv->read_index + 1) %
                                      MON_MSGLIM;
                atomic_dec(&monpriv->read_ready);
                return ERR_PTR(-EOVERFLOW);
        }
        return monmsg;
}


/******************************************************************************
 *                               IUCV handler                                 *
 *****************************************************************************/
static void mon_iucv_path_complete(struct iucv_path *path, u8 *ipuser)
{
        struct mon_private *monpriv = path->private;

        atomic_set(&monpriv->iucv_connected, 1);
        wake_up(&mon_conn_wait_queue);
}

static void mon_iucv_path_severed(struct iucv_path *path, u8 *ipuser)
{
        struct mon_private *monpriv = path->private;

        pr_err("z/VM *MONITOR system service disconnected with rc=%i\n",
               ipuser[0]);
        iucv_path_sever(path, NULL);
        atomic_set(&monpriv->iucv_severed, 1);
        wake_up(&mon_conn_wait_queue);
        wake_up_interruptible(&mon_read_wait_queue);
}

static void mon_iucv_message_pending(struct iucv_path *path,
                                     struct iucv_message *msg)
{
        struct mon_private *monpriv = path->private;

        memcpy(&monpriv->msg_array[monpriv->write_index]->msg,
               msg, sizeof(*msg));
        if (atomic_inc_return(&monpriv->msglim_count) == MON_MSGLIM) {
                pr_warn("The read queue for monitor data is full\n");
                monpriv->msg_array[monpriv->write_index]->msglim_reached = 1;
        }
        monpriv->write_index = (monpriv->write_index + 1) % MON_MSGLIM;
        atomic_inc(&monpriv->read_ready);
        wake_up_interruptible(&mon_read_wait_queue);
}

static struct iucv_handler monreader_iucv_handler = {
        .path_complete   = mon_iucv_path_complete,
        .path_severed    = mon_iucv_path_severed,
        .message_pending = mon_iucv_message_pending,
};

/******************************************************************************
 *                               file operations                              *
 *****************************************************************************/
static int mon_open(struct inode *inode, struct file *filp)
{
        struct mon_private *monpriv;
        int rc;

        /*
         * only one user allowed
         */
        rc = -EBUSY;
        if (test_and_set_bit(MON_IN_USE, &mon_in_use))
                goto out;

        rc = -ENOMEM;
        monpriv = mon_alloc_mem();
        if (!monpriv)
                goto out_use;

        /*
         * Connect to *MONITOR service
         */
        monpriv->path = iucv_path_alloc(MON_MSGLIM, IUCV_IPRMDATA, GFP_KERNEL);
        if (!monpriv->path)
                goto out_priv;
        rc = iucv_path_connect(monpriv->path, &monreader_iucv_handler,
                               MON_SERVICE, NULL, user_data_connect, monpriv);
        if (rc) {
                pr_err("Connecting to the z/VM *MONITOR system service "
                       "failed with rc=%i\n", rc);
                rc = -EIO;
                goto out_path;
        }
        /*
         * Wait for connection confirmation
         */
        wait_event(mon_conn_wait_queue,
                   atomic_read(&monpriv->iucv_connected) ||
                   atomic_read(&monpriv->iucv_severed));
        if (atomic_read(&monpriv->iucv_severed)) {
                atomic_set(&monpriv->iucv_severed, 0);
                atomic_set(&monpriv->iucv_connected, 0);
                rc = -EIO;
                goto out_path;
        }
        filp->private_data = monpriv;
        return nonseekable_open(inode, filp);

out_path:
        iucv_path_free(monpriv->path);
out_priv:
        mon_free_mem(monpriv);
out_use:
        clear_bit(MON_IN_USE, &mon_in_use);
out:
        return rc;
}

static int mon_close(struct inode *inode, struct file *filp)
{
        int rc, i;
        struct mon_private *monpriv = filp->private_data;

        /*
         * Close IUCV connection and unregister
         */
        if (monpriv->path) {
                rc = iucv_path_sever(monpriv->path, user_data_sever);
                if (rc)
                        pr_warn("Disconnecting the z/VM *MONITOR system service failed with rc=%i\n",
                                rc);
                iucv_path_free(monpriv->path);
        }

        atomic_set(&monpriv->iucv_severed, 0);
        atomic_set(&monpriv->iucv_connected, 0);
        atomic_set(&monpriv->read_ready, 0);
        atomic_set(&monpriv->msglim_count, 0);
        monpriv->write_index  = 0;
        monpriv->read_index   = 0;

        for (i = 0; i < MON_MSGLIM; i++)
                kfree(monpriv->msg_array[i]);
        kfree(monpriv);
        clear_bit(MON_IN_USE, &mon_in_use);
        return 0;
}

static ssize_t mon_read(struct file *filp, char __user *data,
                        size_t count, loff_t *ppos)
{
        struct mon_private *monpriv = filp->private_data;
        struct mon_msg *monmsg;
        int ret;
        u32 mce_start;

        monmsg = mon_next_message(monpriv);
        if (IS_ERR(monmsg))
                return PTR_ERR(monmsg);

        if (!monmsg) {
                if (filp->f_flags & O_NONBLOCK)
                        return -EAGAIN;
                ret = wait_event_interruptible(mon_read_wait_queue,
                                        atomic_read(&monpriv->read_ready) ||
                                        atomic_read(&monpriv->iucv_severed));
                if (ret)
                        return ret;
                if (unlikely(atomic_read(&monpriv->iucv_severed)))
                        return -EIO;
                monmsg = monpriv->msg_array[monpriv->read_index];
        }

        if (!monmsg->pos)
                monmsg->pos = mon_mca_start(monmsg) + monmsg->mca_offset;
        if (mon_check_mca(monmsg))
                goto reply;

        /* read monitor control element (12 bytes) first */
        mce_start = mon_mca_start(monmsg) + monmsg->mca_offset;
        if ((monmsg->pos >= mce_start) && (monmsg->pos < mce_start + 12)) {
                count = min(count, (size_t) mce_start + 12 - monmsg->pos);
                ret = copy_to_user(data, __va(monmsg->pos), count);
                if (ret)
                        return -EFAULT;
                monmsg->pos += count;
                if (monmsg->pos == mce_start + 12)
                        monmsg->pos = mon_rec_start(monmsg);
                goto out_copy;
        }

        /* read records */
        if (monmsg->pos <= mon_rec_end(monmsg)) {
                count = min(count, (size_t) mon_rec_end(monmsg) - monmsg->pos
                                            + 1);
                ret = copy_to_user(data, __va(monmsg->pos), count);
                if (ret)
                        return -EFAULT;
                monmsg->pos += count;
                if (monmsg->pos > mon_rec_end(monmsg))
                        mon_next_mca(monmsg);
                goto out_copy;
        }
reply:
        ret = mon_send_reply(monmsg, monpriv);
        return ret;

out_copy:
        *ppos += count;
        return count;
}

static __poll_t mon_poll(struct file *filp, struct poll_table_struct *p)
{
        struct mon_private *monpriv = filp->private_data;

        poll_wait(filp, &mon_read_wait_queue, p);
        if (unlikely(atomic_read(&monpriv->iucv_severed)))
                return EPOLLERR;
        if (atomic_read(&monpriv->read_ready))
                return EPOLLIN | EPOLLRDNORM;
        return 0;
}

static const struct file_operations mon_fops = {
        .owner   = THIS_MODULE,
        .open    = &mon_open,
        .release = &mon_close,
        .read    = &mon_read,
        .poll    = &mon_poll,
        .llseek  = noop_llseek,
};

static struct miscdevice mon_dev = {
        .name       = "monreader",
        .fops       = &mon_fops,
        .minor      = MISC_DYNAMIC_MINOR,
};

/******************************************************************************
 *                              module init/exit                              *
 *****************************************************************************/
static int __init mon_init(void)
{
        int rc;

        if (!machine_is_vm()) {
                pr_err("The z/VM *MONITOR record device driver cannot be "
                       "loaded without z/VM\n");
                return -ENODEV;
        }

        /*
         * Register with IUCV and connect to *MONITOR service
         */
        rc = iucv_register(&monreader_iucv_handler, 1);
        if (rc) {
                pr_err("The z/VM *MONITOR record device driver failed to "
                       "register with IUCV\n");
                return rc;
        }

        rc = segment_type(mon_dcss_name);
        if (rc < 0) {
                segment_warning(rc, mon_dcss_name);
                goto out_iucv;
        }
        if (rc != SEG_TYPE_SC) {
                pr_err("The specified *MONITOR DCSS %s does not have the "
                       "required type SC\n", mon_dcss_name);
                rc = -EINVAL;
                goto out_iucv;
        }

        rc = segment_load(mon_dcss_name, SEGMENT_SHARED,
                          &mon_dcss_start, &mon_dcss_end);
        if (rc < 0) {
                segment_warning(rc, mon_dcss_name);
                rc = -EINVAL;
                goto out_iucv;
        }
        dcss_mkname(mon_dcss_name, &user_data_connect[8]);

        /*
         * misc_register() has to be the last action in module_init(), because
         * file operations will be available right after this.
         */
        rc = misc_register(&mon_dev);
        if (rc < 0 )
                goto out;
        return 0;

out:
        segment_unload(mon_dcss_name);
out_iucv:
        iucv_unregister(&monreader_iucv_handler, 1);
        return rc;
}

static void __exit mon_exit(void)
{
        segment_unload(mon_dcss_name);
        misc_deregister(&mon_dev);
        iucv_unregister(&monreader_iucv_handler, 1);
        return;
}


module_init(mon_init);
module_exit(mon_exit);

module_param_string(mondcss, mon_dcss_name, 9, 0444);
MODULE_PARM_DESC(mondcss, "Name of DCSS segment to be used for *MONITOR "
                 "service, max. 8 chars. Default is MONDCSS");

MODULE_AUTHOR("Gerald Schaefer <geraldsc@de.ibm.com>");
MODULE_DESCRIPTION("Character device driver for reading z/VM "
                   "monitor service records.");
MODULE_LICENSE("GPL");