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[linux-ginger.git] / drivers / char / hvc_iucv.c

/*
 * hvc_iucv.c - z/VM IUCV hypervisor console (HVC) device driver
 *
 * This HVC device driver provides terminal access using
 * z/VM IUCV communication paths.
 *
 * Copyright IBM Corp. 2008, 2009
 *
 * Author(s):   Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
 */
#define KMSG_COMPONENT          "hvc_iucv"
#define pr_fmt(fmt)             KMSG_COMPONENT ": " fmt

#include <linux/types.h>
#include <asm/ebcdic.h>
#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/moduleparam.h>
#include <linux/tty.h>
#include <linux/wait.h>
#include <net/iucv/iucv.h>

#include "hvc_console.h"


/* General device driver settings */
#define HVC_IUCV_MAGIC          0xc9e4c3e5
#define MAX_HVC_IUCV_LINES      HVC_ALLOC_TTY_ADAPTERS
#define MEMPOOL_MIN_NR          (PAGE_SIZE / sizeof(struct iucv_tty_buffer)/4)

/* IUCV TTY message  */
#define MSG_VERSION             0x02    /* Message version */
#define MSG_TYPE_ERROR          0x01    /* Error message */
#define MSG_TYPE_TERMENV        0x02    /* Terminal environment variable */
#define MSG_TYPE_TERMIOS        0x04    /* Terminal IO struct update */
#define MSG_TYPE_WINSIZE        0x08    /* Terminal window size update */
#define MSG_TYPE_DATA           0x10    /* Terminal data */

struct iucv_tty_msg {
        u8      version;                /* Message version */
        u8      type;                   /* Message type */
#define MSG_MAX_DATALEN         ((u16)(~0))
        u16     datalen;                /* Payload length */
        u8      data[];                 /* Payload buffer */
} __attribute__((packed));
#define MSG_SIZE(s)             ((s) + offsetof(struct iucv_tty_msg, data))

enum iucv_state_t {
        IUCV_DISCONN    = 0,
        IUCV_CONNECTED  = 1,
        IUCV_SEVERED    = 2,
};

enum tty_state_t {
        TTY_CLOSED      = 0,
        TTY_OPENED      = 1,
};

struct hvc_iucv_private {
        struct hvc_struct       *hvc;           /* HVC struct reference */
        u8                      srv_name[8];    /* IUCV service name (ebcdic) */
        unsigned char           is_console;     /* Linux console usage flag */
        enum iucv_state_t       iucv_state;     /* IUCV connection status */
        enum tty_state_t        tty_state;      /* TTY status */
        struct iucv_path        *path;          /* IUCV path pointer */
        spinlock_t              lock;           /* hvc_iucv_private lock */
#define SNDBUF_SIZE             (PAGE_SIZE)     /* must be < MSG_MAX_DATALEN */
        void                    *sndbuf;        /* send buffer            */
        size_t                  sndbuf_len;     /* length of send buffer  */
#define QUEUE_SNDBUF_DELAY      (HZ / 25)
        struct delayed_work     sndbuf_work;    /* work: send iucv msg(s) */
        wait_queue_head_t       sndbuf_waitq;   /* wait for send completion */
        struct list_head        tty_outqueue;   /* outgoing IUCV messages */
        struct list_head        tty_inqueue;    /* incoming IUCV messages */
        struct device           *dev;           /* device structure */
};

struct iucv_tty_buffer {
        struct list_head        list;   /* list pointer */
        struct iucv_message     msg;    /* store an IUCV message */
        size_t                  offset; /* data buffer offset */
        struct iucv_tty_msg     *mbuf;  /* buffer to store input/output data */
};

/* IUCV callback handler */
static  int hvc_iucv_path_pending(struct iucv_path *, u8[8], u8[16]);
static void hvc_iucv_path_severed(struct iucv_path *, u8[16]);
static void hvc_iucv_msg_pending(struct iucv_path *, struct iucv_message *);
static void hvc_iucv_msg_complete(struct iucv_path *, struct iucv_message *);


/* Kernel module parameter: use one terminal device as default */
static unsigned long hvc_iucv_devices = 1;

/* Array of allocated hvc iucv tty lines... */
static struct hvc_iucv_private *hvc_iucv_table[MAX_HVC_IUCV_LINES];
#define IUCV_HVC_CON_IDX        (0)
/* List of z/VM user ID filter entries (struct iucv_vmid_filter) */
#define MAX_VMID_FILTER         (500)
static size_t hvc_iucv_filter_size;
static void *hvc_iucv_filter;
static const char *hvc_iucv_filter_string;
static DEFINE_RWLOCK(hvc_iucv_filter_lock);

/* Kmem cache and mempool for iucv_tty_buffer elements */
static struct kmem_cache *hvc_iucv_buffer_cache;
static mempool_t *hvc_iucv_mempool;

/* IUCV handler callback functions */
static struct iucv_handler hvc_iucv_handler = {
        .path_pending  = hvc_iucv_path_pending,
        .path_severed  = hvc_iucv_path_severed,
        .message_complete = hvc_iucv_msg_complete,
        .message_pending  = hvc_iucv_msg_pending,
};


/**
 * hvc_iucv_get_private() - Return a struct hvc_iucv_private instance.
 * @num:        The HVC virtual terminal number (vtermno)
 *
 * This function returns the struct hvc_iucv_private instance that corresponds
 * to the HVC virtual terminal number specified as parameter @num.
 */
struct hvc_iucv_private *hvc_iucv_get_private(uint32_t num)
{
        if ((num < HVC_IUCV_MAGIC) || (num - HVC_IUCV_MAGIC > hvc_iucv_devices))
                return NULL;
        return hvc_iucv_table[num - HVC_IUCV_MAGIC];
}

/**
 * alloc_tty_buffer() - Return a new struct iucv_tty_buffer element.
 * @size:       Size of the internal buffer used to store data.
 * @flags:      Memory allocation flags passed to mempool.
 *
 * This function allocates a new struct iucv_tty_buffer element and, optionally,
 * allocates an internal data buffer with the specified size @size.
 * Note: The total message size arises from the internal buffer size and the
 *       members of the iucv_tty_msg structure.
 * The function returns NULL if memory allocation has failed.
 */
static struct iucv_tty_buffer *alloc_tty_buffer(size_t size, gfp_t flags)
{
        struct iucv_tty_buffer *bufp;

        bufp = mempool_alloc(hvc_iucv_mempool, flags);
        if (!bufp)
                return NULL;
        memset(bufp, 0, sizeof(*bufp));

        if (size > 0) {
                bufp->msg.length = MSG_SIZE(size);
                bufp->mbuf = kmalloc(bufp->msg.length, flags);
                if (!bufp->mbuf) {
                        mempool_free(bufp, hvc_iucv_mempool);
                        return NULL;
                }
                bufp->mbuf->version = MSG_VERSION;
                bufp->mbuf->type    = MSG_TYPE_DATA;
                bufp->mbuf->datalen = (u16) size;
        }
        return bufp;
}

/**
 * destroy_tty_buffer() - destroy struct iucv_tty_buffer element.
 * @bufp:       Pointer to a struct iucv_tty_buffer element, SHALL NOT be NULL.
 */
static void destroy_tty_buffer(struct iucv_tty_buffer *bufp)
{
        kfree(bufp->mbuf);
        mempool_free(bufp, hvc_iucv_mempool);
}

/**
 * destroy_tty_buffer_list() - call destroy_tty_buffer() for each list element.
 * @list:       List containing struct iucv_tty_buffer elements.
 */
static void destroy_tty_buffer_list(struct list_head *list)
{
        struct iucv_tty_buffer *ent, *next;

        list_for_each_entry_safe(ent, next, list, list) {
                list_del(&ent->list);
                destroy_tty_buffer(ent);
        }
}

/**
 * hvc_iucv_write() - Receive IUCV message & write data to HVC buffer.
 * @priv:               Pointer to struct hvc_iucv_private
 * @buf:                HVC buffer for writing received terminal data.
 * @count:              HVC buffer size.
 * @has_more_data:      Pointer to an int variable.
 *
 * The function picks up pending messages from the input queue and receives
 * the message data that is then written to the specified buffer @buf.
 * If the buffer size @count is less than the data message size, the
 * message is kept on the input queue and @has_more_data is set to 1.
 * If all message data has been written, the message is removed from
 * the input queue.
 *
 * The function returns the number of bytes written to the terminal, zero if
 * there are no pending data messages available or if there is no established
 * IUCV path.
 * If the IUCV path has been severed, then -EPIPE is returned to cause a
 * hang up (that is issued by the HVC layer).
 */
static int hvc_iucv_write(struct hvc_iucv_private *priv,
                          char *buf, int count, int *has_more_data)
{
        struct iucv_tty_buffer *rb;
        int written;
        int rc;

        /* immediately return if there is no IUCV connection */
        if (priv->iucv_state == IUCV_DISCONN)
                return 0;

        /* if the IUCV path has been severed, return -EPIPE to inform the
         * HVC layer to hang up the tty device. */
        if (priv->iucv_state == IUCV_SEVERED)
                return -EPIPE;

        /* check if there are pending messages */
        if (list_empty(&priv->tty_inqueue))
                return 0;

        /* receive an iucv message and flip data to the tty (ldisc) */
        rb = list_first_entry(&priv->tty_inqueue, struct iucv_tty_buffer, list);

        written = 0;
        if (!rb->mbuf) { /* message not yet received ... */
                /* allocate mem to store msg data; if no memory is available
                 * then leave the buffer on the list and re-try later */
                rb->mbuf = kmalloc(rb->msg.length, GFP_ATOMIC);
                if (!rb->mbuf)
                        return -ENOMEM;

                rc = __iucv_message_receive(priv->path, &rb->msg, 0,
                                            rb->mbuf, rb->msg.length, NULL);
                switch (rc) {
                case 0: /* Successful       */
                        break;
                case 2: /* No message found */
                case 9: /* Message purged   */
                        break;
                default:
                        written = -EIO;
                }
                /* remove buffer if an error has occured or received data
                 * is not correct */
                if (rc || (rb->mbuf->version != MSG_VERSION) ||
                          (rb->msg.length    != MSG_SIZE(rb->mbuf->datalen)))
                        goto out_remove_buffer;
        }

        switch (rb->mbuf->type) {
        case MSG_TYPE_DATA:
                written = min_t(int, rb->mbuf->datalen - rb->offset, count);
                memcpy(buf, rb->mbuf->data + rb->offset, written);
                if (written < (rb->mbuf->datalen - rb->offset)) {
                        rb->offset += written;
                        *has_more_data = 1;
                        goto out_written;
                }
                break;

        case MSG_TYPE_WINSIZE:
                if (rb->mbuf->datalen != sizeof(struct winsize))
                        break;
                /* The caller must ensure that the hvc is locked, which
                 * is the case when called from hvc_iucv_get_chars() */
                __hvc_resize(priv->hvc, *((struct winsize *) rb->mbuf->data));
                break;

        case MSG_TYPE_ERROR:    /* ignored ... */
        case MSG_TYPE_TERMENV:  /* ignored ... */
        case MSG_TYPE_TERMIOS:  /* ignored ... */
                break;
        }

out_remove_buffer:
        list_del(&rb->list);
        destroy_tty_buffer(rb);
        *has_more_data = !list_empty(&priv->tty_inqueue);

out_written:
        return written;
}

/**
 * hvc_iucv_get_chars() - HVC get_chars operation.
 * @vtermno:    HVC virtual terminal number.
 * @buf:        Pointer to a buffer to store data
 * @count:      Size of buffer available for writing
 *
 * The HVC thread calls this method to read characters from the back-end.
 * If an IUCV communication path has been established, pending IUCV messages
 * are received and data is copied into buffer @buf up to @count bytes.
 *
 * Locking:     The routine gets called under an irqsave() spinlock; and
 *              the routine locks the struct hvc_iucv_private->lock to call
 *              helper functions.
 */
static int hvc_iucv_get_chars(uint32_t vtermno, char *buf, int count)
{
        struct hvc_iucv_private *priv = hvc_iucv_get_private(vtermno);
        int written;
        int has_more_data;

        if (count <= 0)
                return 0;

        if (!priv)
                return -ENODEV;

        spin_lock(&priv->lock);
        has_more_data = 0;
        written = hvc_iucv_write(priv, buf, count, &has_more_data);
        spin_unlock(&priv->lock);

        /* if there are still messages on the queue... schedule another run */
        if (has_more_data)
                hvc_kick();

        return written;
}

/**
 * hvc_iucv_queue() - Buffer terminal data for sending.
 * @priv:       Pointer to struct hvc_iucv_private instance.
 * @buf:        Buffer containing data to send.
 * @count:      Size of buffer and amount of data to send.
 *
 * The function queues data for sending. To actually send the buffered data,
 * a work queue function is scheduled (with QUEUE_SNDBUF_DELAY).
 * The function returns the number of data bytes that has been buffered.
 *
 * If the device is not connected, data is ignored and the function returns
 * @count.
 * If the buffer is full, the function returns 0.
 * If an existing IUCV communicaton path has been severed, -EPIPE is returned
 * (that can be passed to HVC layer to cause a tty hangup).
 */
static int hvc_iucv_queue(struct hvc_iucv_private *priv, const char *buf,
                          int count)
{
        size_t len;

        if (priv->iucv_state == IUCV_DISCONN)
                return count;                   /* ignore data */

        if (priv->iucv_state == IUCV_SEVERED)
                return -EPIPE;

        len = min_t(size_t, count, SNDBUF_SIZE - priv->sndbuf_len);
        if (!len)
                return 0;

        memcpy(priv->sndbuf + priv->sndbuf_len, buf, len);
        priv->sndbuf_len += len;

        if (priv->iucv_state == IUCV_CONNECTED)
                schedule_delayed_work(&priv->sndbuf_work, QUEUE_SNDBUF_DELAY);

        return len;
}

/**
 * hvc_iucv_send() - Send an IUCV message containing terminal data.
 * @priv:       Pointer to struct hvc_iucv_private instance.
 *
 * If an IUCV communication path has been established, the buffered output data
 * is sent via an IUCV message and the number of bytes sent is returned.
 * Returns 0 if there is no established IUCV communication path or
 * -EPIPE if an existing IUCV communicaton path has been severed.
 */
static int hvc_iucv_send(struct hvc_iucv_private *priv)
{
        struct iucv_tty_buffer *sb;
        int rc, len;

        if (priv->iucv_state == IUCV_SEVERED)
                return -EPIPE;

        if (priv->iucv_state == IUCV_DISCONN)
                return -EIO;

        if (!priv->sndbuf_len)
                return 0;

        /* allocate internal buffer to store msg data and also compute total
         * message length */
        sb = alloc_tty_buffer(priv->sndbuf_len, GFP_ATOMIC);
        if (!sb)
                return -ENOMEM;

        memcpy(sb->mbuf->data, priv->sndbuf, priv->sndbuf_len);
        sb->mbuf->datalen = (u16) priv->sndbuf_len;
        sb->msg.length = MSG_SIZE(sb->mbuf->datalen);

        list_add_tail(&sb->list, &priv->tty_outqueue);

        rc = __iucv_message_send(priv->path, &sb->msg, 0, 0,
                                 (void *) sb->mbuf, sb->msg.length);
        if (rc) {
                /* drop the message here; however we might want to handle
                 * 0x03 (msg limit reached) by trying again... */
                list_del(&sb->list);
                destroy_tty_buffer(sb);
        }
        len = priv->sndbuf_len;
        priv->sndbuf_len = 0;

        return len;
}

/**
 * hvc_iucv_sndbuf_work() - Send buffered data over IUCV
 * @work:       Work structure.
 *
 * This work queue function sends buffered output data over IUCV and,
 * if not all buffered data could be sent, reschedules itself.
 */
static void hvc_iucv_sndbuf_work(struct work_struct *work)
{
        struct hvc_iucv_private *priv;

        priv = container_of(work, struct hvc_iucv_private, sndbuf_work.work);
        if (!priv)
                return;

        spin_lock_bh(&priv->lock);
        hvc_iucv_send(priv);
        spin_unlock_bh(&priv->lock);
}

/**
 * hvc_iucv_put_chars() - HVC put_chars operation.
 * @vtermno:    HVC virtual terminal number.
 * @buf:        Pointer to an buffer to read data from
 * @count:      Size of buffer available for reading
 *
 * The HVC thread calls this method to write characters to the back-end.
 * The function calls hvc_iucv_queue() to queue terminal data for sending.
 *
 * Locking:     The method gets called under an irqsave() spinlock; and
 *              locks struct hvc_iucv_private->lock.
 */
static int hvc_iucv_put_chars(uint32_t vtermno, const char *buf, int count)
{
        struct hvc_iucv_private *priv = hvc_iucv_get_private(vtermno);
        int queued;

        if (count <= 0)
                return 0;

        if (!priv)
                return -ENODEV;

        spin_lock(&priv->lock);
        queued = hvc_iucv_queue(priv, buf, count);
        spin_unlock(&priv->lock);

        return queued;
}

/**
 * hvc_iucv_notifier_add() - HVC notifier for opening a TTY for the first time.
 * @hp: Pointer to the HVC device (struct hvc_struct)
 * @id: Additional data (originally passed to hvc_alloc): the index of an struct
 *      hvc_iucv_private instance.
 *
 * The function sets the tty state to TTY_OPENED for the struct hvc_iucv_private
 * instance that is derived from @id. Always returns 0.
 *
 * Locking:     struct hvc_iucv_private->lock, spin_lock_bh
 */
static int hvc_iucv_notifier_add(struct hvc_struct *hp, int id)
{
        struct hvc_iucv_private *priv;

        priv = hvc_iucv_get_private(id);
        if (!priv)
                return 0;

        spin_lock_bh(&priv->lock);
        priv->tty_state = TTY_OPENED;
        spin_unlock_bh(&priv->lock);

        return 0;
}

/**
 * hvc_iucv_cleanup() - Clean up and reset a z/VM IUCV HVC instance.
 * @priv:       Pointer to the struct hvc_iucv_private instance.
 */
static void hvc_iucv_cleanup(struct hvc_iucv_private *priv)
{
        destroy_tty_buffer_list(&priv->tty_outqueue);
        destroy_tty_buffer_list(&priv->tty_inqueue);

        priv->tty_state = TTY_CLOSED;
        priv->iucv_state = IUCV_DISCONN;

        priv->sndbuf_len = 0;
}

/**
 * tty_outqueue_empty() - Test if the tty outq is empty
 * @priv:       Pointer to struct hvc_iucv_private instance.
 */
static inline int tty_outqueue_empty(struct hvc_iucv_private *priv)
{
        int rc;

        spin_lock_bh(&priv->lock);
        rc = list_empty(&priv->tty_outqueue);
        spin_unlock_bh(&priv->lock);

        return rc;
}

/**
 * flush_sndbuf_sync() - Flush send buffer and wait for completion
 * @priv:       Pointer to struct hvc_iucv_private instance.
 *
 * The routine cancels a pending sndbuf work, calls hvc_iucv_send()
 * to flush any buffered terminal output data and waits for completion.
 */
static void flush_sndbuf_sync(struct hvc_iucv_private *priv)
{
        int sync_wait;

        cancel_delayed_work_sync(&priv->sndbuf_work);

        spin_lock_bh(&priv->lock);
        hvc_iucv_send(priv);            /* force sending buffered data */
        sync_wait = !list_empty(&priv->tty_outqueue); /* anything queued ? */
        spin_unlock_bh(&priv->lock);

        if (sync_wait)
                wait_event_timeout(priv->sndbuf_waitq,
                                   tty_outqueue_empty(priv), HZ/10);
}

/**
 * hvc_iucv_hangup() - Sever IUCV path and schedule hvc tty hang up
 * @priv:       Pointer to hvc_iucv_private structure
 *
 * This routine severs an existing IUCV communication path and hangs
 * up the underlying HVC terminal device.
 * The hang-up occurs only if an IUCV communication path is established;
 * otherwise there is no need to hang up the terminal device.
 *
 * The IUCV HVC hang-up is separated into two steps:
 * 1. After the IUCV path has been severed, the iucv_state is set to
 *    IUCV_SEVERED.
 * 2. Later, when the HVC thread calls hvc_iucv_get_chars(), the
 *    IUCV_SEVERED state causes the tty hang-up in the HVC layer.
 *
 * If the tty has not yet been opened, clean up the hvc_iucv_private
 * structure to allow re-connects.
 * If the tty has been opened, let get_chars() return -EPIPE to signal
 * the HVC layer to hang up the tty and, if so, wake up the HVC thread
 * to call get_chars()...
 *
 * Special notes on hanging up a HVC terminal instantiated as console:
 * Hang-up:     1. do_tty_hangup() replaces file ops (= hung_up_tty_fops)
 *              2. do_tty_hangup() calls tty->ops->close() for console_filp
 *                      => no hangup notifier is called by HVC (default)
 *              2. hvc_close() returns because of tty_hung_up_p(filp)
 *                      => no delete notifier is called!
 * Finally, the back-end is not being notified, thus, the tty session is
 * kept active (TTY_OPEN) to be ready for re-connects.
 *
 * Locking:     spin_lock(&priv->lock) w/o disabling bh
 */
static void hvc_iucv_hangup(struct hvc_iucv_private *priv)
{
        struct iucv_path *path;

        path = NULL;
        spin_lock(&priv->lock);
        if (priv->iucv_state == IUCV_CONNECTED) {
                path = priv->path;
                priv->path = NULL;
                priv->iucv_state = IUCV_SEVERED;
                if (priv->tty_state == TTY_CLOSED)
                        hvc_iucv_cleanup(priv);
                else
                        /* console is special (see above) */
                        if (priv->is_console) {
                                hvc_iucv_cleanup(priv);
                                priv->tty_state = TTY_OPENED;
                        } else
                                hvc_kick();
        }
        spin_unlock(&priv->lock);

        /* finally sever path (outside of priv->lock due to lock ordering) */
        if (path) {
                iucv_path_sever(path, NULL);
                iucv_path_free(path);
        }
}

/**
 * hvc_iucv_notifier_hangup() - HVC notifier for TTY hangups.
 * @hp:         Pointer to the HVC device (struct hvc_struct)
 * @id:         Additional data (originally passed to hvc_alloc):
 *              the index of an struct hvc_iucv_private instance.
 *
 * This routine notifies the HVC back-end that a tty hangup (carrier loss,
 * virtual or otherwise) has occured.
 * The z/VM IUCV HVC device driver ignores virtual hangups (vhangup())
 * to keep an existing IUCV communication path established.
 * (Background: vhangup() is called from user space (by getty or login) to
 *              disable writing to the tty by other applications).
 * If the tty has been opened and an established IUCV path has been severed
 * (we caused the tty hangup), the function calls hvc_iucv_cleanup().
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static void hvc_iucv_notifier_hangup(struct hvc_struct *hp, int id)
{
        struct hvc_iucv_private *priv;

        priv = hvc_iucv_get_private(id);
        if (!priv)
                return;

        flush_sndbuf_sync(priv);

        spin_lock_bh(&priv->lock);
        /* NOTE: If the hangup was scheduled by ourself (from the iucv
         *       path_servered callback [IUCV_SEVERED]), we have to clean up
         *       our structure and to set state to TTY_CLOSED.
         *       If the tty was hung up otherwise (e.g. vhangup()), then we
         *       ignore this hangup and keep an established IUCV path open...
         *       (...the reason is that we are not able to connect back to the
         *       client if we disconnect on hang up) */
        priv->tty_state = TTY_CLOSED;

        if (priv->iucv_state == IUCV_SEVERED)
                hvc_iucv_cleanup(priv);
        spin_unlock_bh(&priv->lock);
}

/**
 * hvc_iucv_notifier_del() - HVC notifier for closing a TTY for the last time.
 * @hp:         Pointer to the HVC device (struct hvc_struct)
 * @id:         Additional data (originally passed to hvc_alloc):
 *              the index of an struct hvc_iucv_private instance.
 *
 * This routine notifies the HVC back-end that the last tty device fd has been
 * closed.  The function calls hvc_iucv_cleanup() to clean up the struct
 * hvc_iucv_private instance.
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static void hvc_iucv_notifier_del(struct hvc_struct *hp, int id)
{
        struct hvc_iucv_private *priv;
        struct iucv_path        *path;

        priv = hvc_iucv_get_private(id);
        if (!priv)
                return;

        flush_sndbuf_sync(priv);

        spin_lock_bh(&priv->lock);
        path = priv->path;              /* save reference to IUCV path */
        priv->path = NULL;
        hvc_iucv_cleanup(priv);
        spin_unlock_bh(&priv->lock);

        /* sever IUCV path outside of priv->lock due to lock ordering of:
         * priv->lock <--> iucv_table_lock */
        if (path) {
                iucv_path_sever(path, NULL);
                iucv_path_free(path);
        }
}

/**
 * hvc_iucv_filter_connreq() - Filter connection request based on z/VM user ID
 * @ipvmid:     Originating z/VM user ID (right padded with blanks)
 *
 * Returns 0 if the z/VM user ID @ipvmid is allowed to connection, otherwise
 * non-zero.
 */
static int hvc_iucv_filter_connreq(u8 ipvmid[8])
{
        size_t i;

        /* Note: default policy is ACCEPT if no filter is set */
        if (!hvc_iucv_filter_size)
                return 0;

        for (i = 0; i < hvc_iucv_filter_size; i++)
                if (0 == memcmp(ipvmid, hvc_iucv_filter + (8 * i), 8))
                        return 0;
        return 1;
}

/**
 * hvc_iucv_path_pending() - IUCV handler to process a connection request.
 * @path:       Pending path (struct iucv_path)
 * @ipvmid:     z/VM system identifier of originator
 * @ipuser:     User specified data for this path
 *              (AF_IUCV: port/service name and originator port)
 *
 * The function uses the @ipuser data to determine if the pending path belongs
 * to a terminal managed by this device driver.
 * If the path belongs to this driver, ensure that the terminal is not accessed
 * multiple times (only one connection to a terminal is allowed).
 * If the terminal is not yet connected, the pending path is accepted and is
 * associated to the appropriate struct hvc_iucv_private instance.
 *
 * Returns 0 if @path belongs to a terminal managed by the this device driver;
 * otherwise returns -ENODEV in order to dispatch this path to other handlers.
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static  int hvc_iucv_path_pending(struct iucv_path *path,
                                  u8 ipvmid[8], u8 ipuser[16])
{
        struct hvc_iucv_private *priv;
        u8 nuser_data[16];
        u8 vm_user_id[9];
        int i, rc;

        priv = NULL;
        for (i = 0; i < hvc_iucv_devices; i++)
                if (hvc_iucv_table[i] &&
                    (0 == memcmp(hvc_iucv_table[i]->srv_name, ipuser, 8))) {
                        priv = hvc_iucv_table[i];
                        break;
                }
        if (!priv)
                return -ENODEV;

        /* Enforce that ipvmid is allowed to connect to us */
        read_lock(&hvc_iucv_filter_lock);
        rc = hvc_iucv_filter_connreq(ipvmid);
        read_unlock(&hvc_iucv_filter_lock);
        if (rc) {
                iucv_path_sever(path, ipuser);
                iucv_path_free(path);
                memcpy(vm_user_id, ipvmid, 8);
                vm_user_id[8] = 0;
                pr_info("A connection request from z/VM user ID %s "
                        "was refused\n", vm_user_id);
                return 0;
        }

        spin_lock(&priv->lock);

        /* If the terminal is already connected or being severed, then sever
         * this path to enforce that there is only ONE established communication
         * path per terminal. */
        if (priv->iucv_state != IUCV_DISCONN) {
                iucv_path_sever(path, ipuser);
                iucv_path_free(path);
                goto out_path_handled;
        }

        /* accept path */
        memcpy(nuser_data, ipuser + 8, 8);  /* remote service (for af_iucv) */
        memcpy(nuser_data + 8, ipuser, 8);  /* local service  (for af_iucv) */
        path->msglim = 0xffff;              /* IUCV MSGLIMIT */
        path->flags &= ~IUCV_IPRMDATA;      /* TODO: use IUCV_IPRMDATA */
        rc = iucv_path_accept(path, &hvc_iucv_handler, nuser_data, priv);
        if (rc) {
                iucv_path_sever(path, ipuser);
                iucv_path_free(path);
                goto out_path_handled;
        }
        priv->path = path;
        priv->iucv_state = IUCV_CONNECTED;

        /* flush buffered output data... */
        schedule_delayed_work(&priv->sndbuf_work, 5);

out_path_handled:
        spin_unlock(&priv->lock);
        return 0;
}

/**
 * hvc_iucv_path_severed() - IUCV handler to process a path sever.
 * @path:       Pending path (struct iucv_path)
 * @ipuser:     User specified data for this path
 *              (AF_IUCV: port/service name and originator port)
 *
 * This function calls the hvc_iucv_hangup() function for the
 * respective IUCV HVC terminal.
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static void hvc_iucv_path_severed(struct iucv_path *path, u8 ipuser[16])
{
        struct hvc_iucv_private *priv = path->private;

        hvc_iucv_hangup(priv);
}

/**
 * hvc_iucv_msg_pending() - IUCV handler to process an incoming IUCV message.
 * @path:       Pending path (struct iucv_path)
 * @msg:        Pointer to the IUCV message
 *
 * The function puts an incoming message on the input queue for later
 * processing (by hvc_iucv_get_chars() / hvc_iucv_write()).
 * If the tty has not yet been opened, the message is rejected.
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static void hvc_iucv_msg_pending(struct iucv_path *path,
                                 struct iucv_message *msg)
{
        struct hvc_iucv_private *priv = path->private;
        struct iucv_tty_buffer *rb;

        /* reject messages that exceed max size of iucv_tty_msg->datalen */
        if (msg->length > MSG_SIZE(MSG_MAX_DATALEN)) {
                iucv_message_reject(path, msg);
                return;
        }

        spin_lock(&priv->lock);

        /* reject messages if tty has not yet been opened */
        if (priv->tty_state == TTY_CLOSED) {
                iucv_message_reject(path, msg);
                goto unlock_return;
        }

        /* allocate tty buffer to save iucv msg only */
        rb = alloc_tty_buffer(0, GFP_ATOMIC);
        if (!rb) {
                iucv_message_reject(path, msg);
                goto unlock_return;     /* -ENOMEM */
        }
        rb->msg = *msg;

        list_add_tail(&rb->list, &priv->tty_inqueue);

        hvc_kick();     /* wake up hvc thread */

unlock_return:
        spin_unlock(&priv->lock);
}

/**
 * hvc_iucv_msg_complete() - IUCV handler to process message completion
 * @path:       Pending path (struct iucv_path)
 * @msg:        Pointer to the IUCV message
 *
 * The function is called upon completion of message delivery to remove the
 * message from the outqueue. Additional delivery information can be found
 * msg->audit: rejected messages (0x040000 (IPADRJCT)), and
 *             purged messages   (0x010000 (IPADPGNR)).
 *
 * Locking:     struct hvc_iucv_private->lock
 */
static void hvc_iucv_msg_complete(struct iucv_path *path,
                                  struct iucv_message *msg)
{
        struct hvc_iucv_private *priv = path->private;
        struct iucv_tty_buffer  *ent, *next;
        LIST_HEAD(list_remove);

        spin_lock(&priv->lock);
        list_for_each_entry_safe(ent, next, &priv->tty_outqueue, list)
                if (ent->msg.id == msg->id) {
                        list_move(&ent->list, &list_remove);
                        break;
                }
        wake_up(&priv->sndbuf_waitq);
        spin_unlock(&priv->lock);
        destroy_tty_buffer_list(&list_remove);
}

/**
 * hvc_iucv_pm_freeze() - Freeze PM callback
 * @dev:        IUVC HVC terminal device
 *
 * Sever an established IUCV communication path and
 * trigger a hang-up of the underlying HVC terminal.
 */
static int hvc_iucv_pm_freeze(struct device *dev)
{
        struct hvc_iucv_private *priv = dev_get_drvdata(dev);

        local_bh_disable();
        hvc_iucv_hangup(priv);
        local_bh_enable();

        return 0;
}

/**
 * hvc_iucv_pm_restore_thaw() - Thaw and restore PM callback
 * @dev:        IUVC HVC terminal device
 *
 * Wake up the HVC thread to trigger hang-up and respective
 * HVC back-end notifier invocations.
 */
static int hvc_iucv_pm_restore_thaw(struct device *dev)
{
        hvc_kick();
        return 0;
}


/* HVC operations */
static struct hv_ops hvc_iucv_ops = {
        .get_chars = hvc_iucv_get_chars,
        .put_chars = hvc_iucv_put_chars,
        .notifier_add = hvc_iucv_notifier_add,
        .notifier_del = hvc_iucv_notifier_del,
        .notifier_hangup = hvc_iucv_notifier_hangup,
};

/* Suspend / resume device operations */
static struct dev_pm_ops hvc_iucv_pm_ops = {
        .freeze   = hvc_iucv_pm_freeze,
        .thaw     = hvc_iucv_pm_restore_thaw,
        .restore  = hvc_iucv_pm_restore_thaw,
};

/* IUCV HVC device driver */
static struct device_driver hvc_iucv_driver = {
        .name = KMSG_COMPONENT,
        .bus  = &iucv_bus,
        .pm   = &hvc_iucv_pm_ops,
};

/**
 * hvc_iucv_alloc() - Allocates a new struct hvc_iucv_private instance
 * @id:                 hvc_iucv_table index
 * @is_console:         Flag if the instance is used as Linux console
 *
 * This function allocates a new hvc_iucv_private structure and stores
 * the instance in hvc_iucv_table at index @id.
 * Returns 0 on success; otherwise non-zero.
 */
static int __init hvc_iucv_alloc(int id, unsigned int is_console)
{
        struct hvc_iucv_private *priv;
        char name[9];
        int rc;

        priv = kzalloc(sizeof(struct hvc_iucv_private), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        spin_lock_init(&priv->lock);
        INIT_LIST_HEAD(&priv->tty_outqueue);
        INIT_LIST_HEAD(&priv->tty_inqueue);
        INIT_DELAYED_WORK(&priv->sndbuf_work, hvc_iucv_sndbuf_work);
        init_waitqueue_head(&priv->sndbuf_waitq);

        priv->sndbuf = (void *) get_zeroed_page(GFP_KERNEL);
        if (!priv->sndbuf) {
                kfree(priv);
                return -ENOMEM;
        }

        /* set console flag */
        priv->is_console = is_console;

        /* allocate hvc device */
        priv->hvc = hvc_alloc(HVC_IUCV_MAGIC + id, /*             PAGE_SIZE */
                              HVC_IUCV_MAGIC + id, &hvc_iucv_ops, 256);
        if (IS_ERR(priv->hvc)) {
                rc = PTR_ERR(priv->hvc);
                goto out_error_hvc;
        }

        /* notify HVC thread instead of using polling */
        priv->hvc->irq_requested = 1;

        /* setup iucv related information */
        snprintf(name, 9, "lnxhvc%-2d", id);
        memcpy(priv->srv_name, name, 8);
        ASCEBC(priv->srv_name, 8);

        /* create and setup device */
        priv->dev = kzalloc(sizeof(*priv->dev), GFP_KERNEL);
        if (!priv->dev) {
                rc = -ENOMEM;
                goto out_error_dev;
        }
        dev_set_name(priv->dev, "hvc_iucv%d", id);
        dev_set_drvdata(priv->dev, priv);
        priv->dev->bus = &iucv_bus;
        priv->dev->parent = iucv_root;
        priv->dev->driver = &hvc_iucv_driver;
        priv->dev->release = (void (*)(struct device *)) kfree;
        rc = device_register(priv->dev);
        if (rc) {
                put_device(priv->dev);
                goto out_error_dev;
        }

        hvc_iucv_table[id] = priv;
        return 0;

out_error_dev:
        hvc_remove(priv->hvc);
out_error_hvc:
        free_page((unsigned long) priv->sndbuf);
        kfree(priv);

        return rc;
}

/**
 * hvc_iucv_destroy() - Destroy and free hvc_iucv_private instances
 */
static void __init hvc_iucv_destroy(struct hvc_iucv_private *priv)
{
        hvc_remove(priv->hvc);
        device_unregister(priv->dev);
        free_page((unsigned long) priv->sndbuf);
        kfree(priv);
}

/**
 * hvc_iucv_parse_filter() - Parse filter for a single z/VM user ID
 * @filter:     String containing a comma-separated list of z/VM user IDs
 */
static const char *hvc_iucv_parse_filter(const char *filter, char *dest)
{
        const char *nextdelim, *residual;
        size_t len;

        nextdelim = strchr(filter, ',');
        if (nextdelim) {
                len = nextdelim - filter;
                residual = nextdelim + 1;
        } else {
                len = strlen(filter);
                residual = filter + len;
        }

        if (len == 0)
                return ERR_PTR(-EINVAL);

        /* check for '\n' (if called from sysfs) */
        if (filter[len - 1] == '\n')
                len--;

        if (len > 8)
                return ERR_PTR(-EINVAL);

        /* pad with blanks and save upper case version of user ID */
        memset(dest, ' ', 8);
        while (len--)
                dest[len] = toupper(filter[len]);
        return residual;
}

/**
 * hvc_iucv_setup_filter() - Set up z/VM user ID filter
 * @filter:     String consisting of a comma-separated list of z/VM user IDs
 *
 * The function parses the @filter string and creates an array containing
 * the list of z/VM user ID filter entries.
 * Return code 0 means success, -EINVAL if the filter is syntactically
 * incorrect, -ENOMEM if there was not enough memory to allocate the
 * filter list array, or -ENOSPC if too many z/VM user IDs have been specified.
 */
static int hvc_iucv_setup_filter(const char *val)
{
        const char *residual;
        int err;
        size_t size, count;
        void *array, *old_filter;

        count = strlen(val);
        if (count == 0 || (count == 1 && val[0] == '\n')) {
                size  = 0;
                array = NULL;
                goto out_replace_filter;        /* clear filter */
        }

        /* count user IDs in order to allocate sufficient memory */
        size = 1;
        residual = val;
        while ((residual = strchr(residual, ',')) != NULL) {
                residual++;
                size++;
        }

        /* check if the specified list exceeds the filter limit */
        if (size > MAX_VMID_FILTER)
                return -ENOSPC;

        array = kzalloc(size * 8, GFP_KERNEL);
        if (!array)
                return -ENOMEM;

        count = size;
        residual = val;
        while (*residual && count) {
                residual = hvc_iucv_parse_filter(residual,
                                                 array + ((size - count) * 8));
                if (IS_ERR(residual)) {
                        err = PTR_ERR(residual);
                        kfree(array);
                        goto out_err;
                }
                count--;
        }

out_replace_filter:
        write_lock_bh(&hvc_iucv_filter_lock);
        old_filter = hvc_iucv_filter;
        hvc_iucv_filter_size = size;
        hvc_iucv_filter = array;
        write_unlock_bh(&hvc_iucv_filter_lock);
        kfree(old_filter);

        err = 0;
out_err:
        return err;
}

/**
 * param_set_vmidfilter() - Set z/VM user ID filter parameter
 * @val:        String consisting of a comma-separated list of z/VM user IDs
 * @kp:         Kernel parameter pointing to hvc_iucv_filter array
 *
 * The function sets up the z/VM user ID filter specified as comma-separated
 * list of user IDs in @val.
 * Note: If it is called early in the boot process, @val is stored and
 *       parsed later in hvc_iucv_init().
 */
static int param_set_vmidfilter(const char *val, struct kernel_param *kp)
{
        int rc;

        if (!MACHINE_IS_VM || !hvc_iucv_devices)
                return -ENODEV;

        if (!val)
                return -EINVAL;

        rc = 0;
        if (slab_is_available())
                rc = hvc_iucv_setup_filter(val);
        else
                hvc_iucv_filter_string = val;   /* defer... */
        return rc;
}

/**
 * param_get_vmidfilter() - Get z/VM user ID filter
 * @buffer:     Buffer to store z/VM user ID filter,
 *              (buffer size assumption PAGE_SIZE)
 * @kp:         Kernel parameter pointing to the hvc_iucv_filter array
 *
 * The function stores the filter as a comma-separated list of z/VM user IDs
 * in @buffer. Typically, sysfs routines call this function for attr show.
 */
static int param_get_vmidfilter(char *buffer, struct kernel_param *kp)
{
        int rc;
        size_t index, len;
        void *start, *end;

        if (!MACHINE_IS_VM || !hvc_iucv_devices)
                return -ENODEV;

        rc = 0;
        read_lock_bh(&hvc_iucv_filter_lock);
        for (index = 0; index < hvc_iucv_filter_size; index++) {
                start = hvc_iucv_filter + (8 * index);
                end   = memchr(start, ' ', 8);
                len   = (end) ? end - start : 8;
                memcpy(buffer + rc, start, len);
                rc += len;
                buffer[rc++] = ',';
        }
        read_unlock_bh(&hvc_iucv_filter_lock);
        if (rc)
                buffer[--rc] = '\0';    /* replace last comma and update rc */
        return rc;
}

#define param_check_vmidfilter(name, p) __param_check(name, p, void)

/**
 * hvc_iucv_init() - z/VM IUCV HVC device driver initialization
 */
static int __init hvc_iucv_init(void)
{
        int rc;
        unsigned int i;

        if (!hvc_iucv_devices)
                return -ENODEV;

        if (!MACHINE_IS_VM) {
                pr_notice("The z/VM IUCV HVC device driver cannot "
                           "be used without z/VM\n");
                rc = -ENODEV;
                goto out_error;
        }

        if (hvc_iucv_devices > MAX_HVC_IUCV_LINES) {
                pr_err("%lu is not a valid value for the hvc_iucv= "
                        "kernel parameter\n", hvc_iucv_devices);
                rc = -EINVAL;
                goto out_error;
        }

        /* register IUCV HVC device driver */
        rc = driver_register(&hvc_iucv_driver);
        if (rc)
                goto out_error;

        /* parse hvc_iucv_allow string and create z/VM user ID filter list */
        if (hvc_iucv_filter_string) {
                rc = hvc_iucv_setup_filter(hvc_iucv_filter_string);
                switch (rc) {
                case 0:
                        break;
                case -ENOMEM:
                        pr_err("Allocating memory failed with "
                                "reason code=%d\n", 3);
                        goto out_error;
                case -EINVAL:
                        pr_err("hvc_iucv_allow= does not specify a valid "
                                "z/VM user ID list\n");
                        goto out_error;
                case -ENOSPC:
                        pr_err("hvc_iucv_allow= specifies too many "
                                "z/VM user IDs\n");
                        goto out_error;
                default:
                        goto out_error;
                }
        }

        hvc_iucv_buffer_cache = kmem_cache_create(KMSG_COMPONENT,
                                           sizeof(struct iucv_tty_buffer),
                                           0, 0, NULL);
        if (!hvc_iucv_buffer_cache) {
                pr_err("Allocating memory failed with reason code=%d\n", 1);
                rc = -ENOMEM;
                goto out_error;
        }

        hvc_iucv_mempool = mempool_create_slab_pool(MEMPOOL_MIN_NR,
                                                    hvc_iucv_buffer_cache);
        if (!hvc_iucv_mempool) {
                pr_err("Allocating memory failed with reason code=%d\n", 2);
                kmem_cache_destroy(hvc_iucv_buffer_cache);
                rc = -ENOMEM;
                goto out_error;
        }

        /* register the first terminal device as console
         * (must be done before allocating hvc terminal devices) */
        rc = hvc_instantiate(HVC_IUCV_MAGIC, IUCV_HVC_CON_IDX, &hvc_iucv_ops);
        if (rc) {
                pr_err("Registering HVC terminal device as "
                       "Linux console failed\n");
                goto out_error_memory;
        }

        /* allocate hvc_iucv_private structs */
        for (i = 0; i < hvc_iucv_devices; i++) {
                rc = hvc_iucv_alloc(i, (i == IUCV_HVC_CON_IDX) ? 1 : 0);
                if (rc) {
                        pr_err("Creating a new HVC terminal device "
                                "failed with error code=%d\n", rc);
                        goto out_error_hvc;
                }
        }

        /* register IUCV callback handler */
        rc = iucv_register(&hvc_iucv_handler, 0);
        if (rc) {
                pr_err("Registering IUCV handlers failed with error code=%d\n",
                        rc);
                goto out_error_iucv;
        }

        return 0;

out_error_iucv:
        iucv_unregister(&hvc_iucv_handler, 0);
out_error_hvc:
        for (i = 0; i < hvc_iucv_devices; i++)
                if (hvc_iucv_table[i])
                        hvc_iucv_destroy(hvc_iucv_table[i]);
out_error_memory:
        mempool_destroy(hvc_iucv_mempool);
        kmem_cache_destroy(hvc_iucv_buffer_cache);
out_error:
        if (hvc_iucv_filter)
                kfree(hvc_iucv_filter);
        hvc_iucv_devices = 0; /* ensure that we do not provide any device */
        return rc;
}

/**
 * hvc_iucv_config() - Parsing of hvc_iucv=  kernel command line parameter
 * @val:        Parameter value (numeric)
 */
static  int __init hvc_iucv_config(char *val)
{
         return strict_strtoul(val, 10, &hvc_iucv_devices);
}


device_initcall(hvc_iucv_init);
__setup("hvc_iucv=", hvc_iucv_config);
core_param(hvc_iucv_allow, hvc_iucv_filter, vmidfilter, 0640);