[S390] s390/hvc_console: z/VM IUCV hypervisor console support

This patch introduces a new hypervisor console (HVC) back-end that provides
terminal access over the z/VM inter-user communication vehicle (IUCV).

The z/VM IUCV communication is independent of the regular tcp/ip network
and allows access even if there is no network connection between two
z/VM guest virtual machines.
The z/VM IUCV hypervisor console back-end helps the user to access a
z/VM guest virtual machine that lacks of network connectivity; and thus,
provides a "full-screen" terminal alternative to 3215/3270 terminal sessions.

Use the hvc_iucv=[0..8] kernel boot parameter to specify the number of
HVC terminals using a z/VM IUCV back-end.

A recent version of the s390-tools package is required to establish a
terminal connection to a z/VM IUCV hypervisor console back-end.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 850 insertions, 0 deletions

diff --git a/drivers/char/hvc_iucv.c b/drivers/char/hvc_iucv.c
new file mode 100644
index 000000000000..5ea7d7713fca
--- /dev/null
+++ b/drivers/char/hvc_iucv.c
@@ -0,0 +1,850 @@
+/*
+ * hvc_iucv.c - z/VM IUCV back-end for the Hypervisor Console (HVC)
+ *
+ * This back-end for HVC provides terminal access via
+ * z/VM IUCV communication paths.
+ *
+ * Copyright IBM Corp. 2008.
+ *
+ * Author(s):   Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
+ */
+#define KMSG_COMPONENT          "hvc_iucv"
+
+#include <linux/types.h>
+#include <asm/ebcdic.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/tty.h>
+#include <net/iucv/iucv.h>
+
+#include "hvc_console.h"
+
+
+/* HVC backend for z/VM IUCV */
+#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 */
+
+#define MSG_SIZE(s)             ((s) + offsetof(struct iucv_tty_msg, 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));
+
+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 console struct reference */
+        u8                      srv_name[8];    /* IUCV service name (ebcdic) */
+        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 */
+        struct list_head        tty_outqueue;   /* outgoing IUCV messages */
+        struct list_head        tty_inqueue;    /* incoming IUCV messages */
+};
+
+struct iucv_tty_buffer {
+        struct list_head        list;   /* list pointer */
+        struct iucv_message     msg;    /* store an incoming 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 parameters */
+static unsigned long hvc_iucv_devices;
+
+/* Array of allocated hvc iucv tty lines... */
+static struct hvc_iucv_private *hvc_iucv_table[MAX_HVC_IUCV_LINES];
+
+/* 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() - Returns 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(struct iucv_tty_buffer));
+
+        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.
+ *
+ * The destroy_tty_buffer() function frees the internal data buffer and returns
+ * the struct iucv_tty_buffer element back to the mempool for freeing.
+ */
+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 head pointer to a list containing struct iucv_tty_buffer
+ *              elements.
+ *
+ * Calls destroy_tty_buffer() for each struct iucv_tty_buffer element in the
+ * list @list.
+ */
+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 console buffer.
+ * @priv:               Pointer to hvc_iucv_private structure.
+ * @buf:                HVC console buffer for writing received terminal data.
+ * @count:              HVC console 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, then the
+ * message is kept on the input queue and @has_more_data is set to 1.
+ * If the message data has been entirely 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 console 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 console 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 a 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;
+                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_console thread calls this method to read characters from
+ * the terminal backend. 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_send() - Send an IUCV message containing terminal data.
+ * @priv:       Pointer to struct hvc_iucv_private instance.
+ * @buf:        Buffer containing data to send.
+ * @size:       Size of buffer and amount of data to send.
+ *
+ * If an IUCV communication path is established, the function copies the buffer
+ * data to a newly allocated struct iucv_tty_buffer element, sends the data and
+ * puts the element to the outqueue.
+ *
+ * If there is no IUCV communication path established, the function returns 0.
+ * If an existing IUCV communicaton path has been severed, the function returns
+ * -EPIPE (can be passed to HVC layer to cause a tty hangup).
+ */
+static int hvc_iucv_send(struct hvc_iucv_private *priv, const char *buf,
+                         int count)
+{
+        struct iucv_tty_buffer *sb;
+        int rc;
+        u16 len;
+
+        if (priv->iucv_state == IUCV_SEVERED)
+                return -EPIPE;
+
+        if (priv->iucv_state == IUCV_DISCONN)
+                return 0;
+
+        len = min_t(u16, MSG_MAX_DATALEN, count);
+
+        /* allocate internal buffer to store msg data and also compute total
+         * message length */
+        sb = alloc_tty_buffer(len, GFP_ATOMIC);
+        if (!sb)
+                return -ENOMEM;
+
+        sb->mbuf->datalen = len;
+        memcpy(sb->mbuf->data, buf, len);
+
+        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) {
+                list_del(&sb->list);
+                destroy_tty_buffer(sb);
+                len = 0;
+        }
+
+        return len;
+}
+
+/**
+ * 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_console thread calls this method to write characters from
+ * to the terminal backend.
+ * The function calls hvc_iucv_send() under the lock of the
+ * struct hvc_iucv_private instance that corresponds to the tty @vtermno.
+ *
+ * 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 sent;
+
+        if (count <= 0)
+                return 0;
+
+        if (!priv)
+                return -ENODEV;
+
+        spin_lock(&priv->lock);
+        sent = hvc_iucv_send(priv, buf, count);
+        spin_unlock(&priv->lock);
+
+        return sent;
+}
+
+/**
+ * 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_OPEN 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 function if the tty portion is finally closed.
+ * @priv:       Pointer to the struct hvc_iucv_private instance.
+ *
+ * The functions severs the established IUCV communication path (if any), and
+ * destroy struct iucv_tty_buffer elements from the in- and outqueue. Finally,
+ * the functions resets the states to TTY_CLOSED and IUCV_DISCONN.
+ */
+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;
+}
+
+/**
+ * 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 backend that a tty hangup (carrier loss,
+ * virtual or otherwise) has occured.
+ *
+ * The HVC backend for z/VM IUCV 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 (e.g. getty) and an established IUCV path has been
+ * severed (we caused the tty hangup in that case), then the functions invokes
+ * hvc_iucv_cleanup() to clean up.
+ *
+ * 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;
+
+        spin_lock_bh(&priv->lock);
+        /* NOTE: If the hangup was scheduled by ourself (from the iucv
+         *       path_servered callback [IUCV_SEVERED]), then we have to
+         *       finally clean up the tty backend structure and 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 backend that the last tty device file
+ * descriptor 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;
+
+        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_path_pending() - IUCV handler to process a connection request.
+ * @path:       Pending path (struct iucv_path)
+ * @ipvmid:     Originator z/VM system identifier
+ * @ipuser:     User specified data for this path
+ *              (AF_IUCV: port/service name and originator port)
+ *
+ * The function uses the @ipuser data to check to determine if the pending
+ * path belongs to a terminal managed by this HVC backend.
+ * If the check is successful, then an additional check is done to ensure
+ * that a terminal cannot be accessed multiple times (only one connection
+ * to a terminal is allowed). In that particular case, the pending path is
+ * severed. If it is the first connection, the pending path is accepted and
+ * associated to the struct hvc_iucv_private. The iucv state is updated to
+ * reflect that a communication path has been established.
+ *
+ * Returns 0 if the path belongs to a terminal managed by the this HVC backend;
+ * 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];
+        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;
+
+        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;
+
+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)
+ *
+ * The function also severs the path (as required by the IUCV protocol) and
+ * sets the iucv state to IUCV_SEVERED for the associated struct
+ * hvc_iucv_private instance. Later, the IUCV_SEVERED state triggers a tty
+ * hangup (hvc_iucv_get_chars() / hvc_iucv_write()).
+ *
+ * If tty portion of the HVC is closed then clean up the outqueue in addition.
+ *
+ * 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;
+
+        spin_lock(&priv->lock);
+        priv->iucv_state = IUCV_SEVERED;
+
+        /* NOTE: If the tty has not yet been opened by a getty program
+         *       (e.g. to see console messages), then cleanup the
+         *       hvc_iucv_private structure to allow re-connects.
+         *
+         *       If the tty has been opened, the get_chars() callback returns
+         *       -EPIPE to signal the hvc console layer to hang up the tty. */
+        priv->path = NULL;
+        if (priv->tty_state == TTY_CLOSED)
+                hvc_iucv_cleanup(priv);
+        spin_unlock(&priv->lock);
+
+        /* finally sever path (outside of priv->lock due to lock ordering) */
+        iucv_path_sever(path, ipuser);
+        iucv_path_free(path);
+}
+
+/**
+ * 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 stores an incoming message on the input queue for later
+ * processing (by hvc_iucv_get_chars() / hvc_iucv_write()).
+ * However, 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;
+
+        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 buffer an empty buffer element */
+        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();     /* wakup hvc console 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 and the
+ * message is removed from the outqueue. Additional delivery information
+ * can be found in 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;
+                }
+        spin_unlock(&priv->lock);
+        destroy_tty_buffer_list(&list_remove);
+}
+
+
+/* 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,
+};
+
+/**
+ * hvc_iucv_alloc() - Allocates a new struct hvc_iucv_private instance
+ * @id: hvc_iucv_table index
+ *
+ * This function allocates a new hvc_iucv_private struct and put the
+ * instance into hvc_iucv_table at index @id.
+ * Returns 0 on success; otherwise non-zero.
+ */
+static int __init hvc_iucv_alloc(int id)
+{
+        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);
+
+        /* Finally allocate hvc */
+        priv->hvc = hvc_alloc(HVC_IUCV_MAGIC + id,
+                              HVC_IUCV_MAGIC + id, &hvc_iucv_ops, PAGE_SIZE);
+        if (IS_ERR(priv->hvc)) {
+                rc = PTR_ERR(priv->hvc);
+                kfree(priv);
+                return rc;
+        }
+
+        /* setup iucv related information */
+        snprintf(name, 9, "ihvc%-4d", id);
+        memcpy(priv->srv_name, name, 8);
+        ASCEBC(priv->srv_name, 8);
+
+        hvc_iucv_table[id] = priv;
+        return 0;
+}
+
+/**
+ * hvc_iucv_init() - Initialization of HVC backend for z/VM IUCV
+ */
+static int __init hvc_iucv_init(void)
+{
+        int rc, i;
+
+        if (!MACHINE_IS_VM) {
+                pr_warning("The z/VM IUCV Hypervisor console cannot be "
+                           "used without z/VM.\n");
+                return -ENODEV;
+        }
+
+        if (!hvc_iucv_devices)
+                return -ENODEV;
+
+        if (hvc_iucv_devices > MAX_HVC_IUCV_LINES)
+                return -EINVAL;
+
+        hvc_iucv_buffer_cache = kmem_cache_create(KMSG_COMPONENT,
+                                           sizeof(struct iucv_tty_buffer),
+                                           0, 0, NULL);
+        if (!hvc_iucv_buffer_cache) {
+                pr_err("Not enough memory for driver initialization "
+                        "(rs=%d).\n", 1);
+                return -ENOMEM;
+        }
+
+        hvc_iucv_mempool = mempool_create_slab_pool(MEMPOOL_MIN_NR,
+                                                    hvc_iucv_buffer_cache);
+        if (!hvc_iucv_mempool) {
+                pr_err("Not enough memory for driver initialization "
+                        "(rs=%d).\n", 2);
+                kmem_cache_destroy(hvc_iucv_buffer_cache);
+                return -ENOMEM;
+        }
+
+        /* allocate hvc_iucv_private structs */
+        for (i = 0; i < hvc_iucv_devices; i++) {
+                rc = hvc_iucv_alloc(i);
+                if (rc) {
+                        pr_err("Could not create new z/VM IUCV HVC backend "
+                                "rc=%d.\n", rc);
+                        goto out_error_hvc;
+                }
+        }
+
+        /* register IUCV callback handler */
+        rc = iucv_register(&hvc_iucv_handler, 0);
+        if (rc) {
+                pr_err("Could not register iucv handler (rc=%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]) {
+                        if (hvc_iucv_table[i]->hvc)
+                                hvc_remove(hvc_iucv_table[i]->hvc);
+                        kfree(hvc_iucv_table[i]);
+                }
+        mempool_destroy(hvc_iucv_mempool);
+        kmem_cache_destroy(hvc_iucv_buffer_cache);
+        return rc;
+}
+
+/**
+ * hvc_iucv_console_init() - Early console initialization
+ */
+static  int __init hvc_iucv_console_init(void)
+{
+        if (!MACHINE_IS_VM || !hvc_iucv_devices)
+                return -ENODEV;
+        return hvc_instantiate(HVC_IUCV_MAGIC, 0, &hvc_iucv_ops);
+}
+
+/**
+ * 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);
+}
+
+
+module_init(hvc_iucv_init);
+console_initcall(hvc_iucv_console_init);
+__setup("hvc_iucv=", hvc_iucv_config);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("HVC back-end for z/VM IUCV.");
+MODULE_AUTHOR("Hendrik Brueckner <brueckner@linux.vnet.ibm.com>");