Basic support for using channel-attached 3270 'green-screen'

devices via tn3270. Actual handling of the data stream is
 delegated to x3270; more info at http://wiki.qemu.org/Features/3270
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Merge remote-tracking branch 'cohuck/tags/s390x-3270-20170504' into staging

Basic support for using channel-attached 3270 'green-screen'
devices via tn3270. Actual handling of the data stream is
delegated to x3270; more info at http://wiki.qemu.org/Features/3270

# gpg: Signature made Thu 04 May 2017 11:36:51 AM BST
# gpg:                using RSA key 0xDECF6B93C6F02FAF
# gpg: Good signature from "Cornelia Huck <conny@cornelia-huck.de>"
# gpg:                 aka "Cornelia Huck <cohuck@kernel.org>"
# gpg:                 aka "Cornelia Huck <cornelia.huck@de.ibm.com>"
# gpg:                 aka "Cornelia Huck <huckc@linux.vnet.ibm.com>"
# Primary key fingerprint: C3D0 D66D C362 4FF6 A8C0  18CE DECF 6B93 C6F0 2FAF

* cohuck/tags/s390x-3270-20170504:
  s390x/3270: Mark non-migratable and enable the device
  s390x/3270: Detect for continued presence of a 3270 client
  s390x/3270: Add the TCP socket events handler for 3270
  s390x/3270: 3270 data stream handling
  s390x/3270: Add emulated terminal3270 device
  s390x/3270: Add abstract emulated ccw-attached 3270 device
  s390x/css: Add an algorithm to find a free chpid
  chardev: Basic support for TN3270

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

chardev/char-socket.c

@@ -55,6 +55,7 @@ typedef struct {
     SocketAddress *addr;
     bool is_listen;
     bool is_telnet;
+    bool is_tn3270;
 
     guint reconnect_timer;
     int64_t reconnect_time;
@@ -141,19 +142,25 @@ static int tcp_chr_read_poll(void *opaque)
     return s->max_size;
 }
 
-#define IAC 255
-#define IAC_BREAK 243
 static void tcp_chr_process_IAC_bytes(Chardev *chr,
                                       SocketChardev *s,
                                       uint8_t *buf, int *size)
 {
-    /* Handle any telnet client's basic IAC options to satisfy char by
+    /* Handle any telnet or tn3270 client's basic IAC options.
-     * char mode with no echo.  All IAC options will be removed from
+     * For telnet options, it satisfies char by char mode with no echo.
-     * the buf and the do_telnetopt variable will be used to track the
+     * For tn3270 options, it satisfies binary mode with EOR.
-     * state of the width of the IAC information.
+     * All IAC options will be removed from the buf and the do_opt
+     * pointer will be used to track the state of the width of the
+     * IAC information.
      *
-     * IAC commands come in sets of 3 bytes with the exception of the
+     * RFC854: "All TELNET commands consist of at least a two byte sequence.
-     * "IAC BREAK" command and the double IAC.
+     * The commands dealing with option negotiation are three byte sequences,
+     * the third byte being the code for the option referenced."
+     * "IAC BREAK", "IAC IP", "IAC NOP" and the double IAC are two bytes.
+     * "IAC SB", "IAC SE" and "IAC EOR" are saved to split up data boundary
+     * for tn3270.
+     * NOP, Break and Interrupt Process(IP) might be encountered during a TN3270
+     * session, and NOP and IP need to be done later.
      */
 
     int i;
@@ -174,6 +181,18 @@ static void tcp_chr_process_IAC_bytes(Chardev *chr,
                     /* Handle IAC break commands by sending a serial break */
                     qemu_chr_be_event(chr, CHR_EVENT_BREAK);
                     s->do_telnetopt++;
+                } else if (s->is_tn3270 && ((unsigned char)buf[i] == IAC_EOR
+                           || (unsigned char)buf[i] == IAC_SB
+                           || (unsigned char)buf[i] == IAC_SE)
+                           && s->do_telnetopt == 2) {
+                    buf[j++] = IAC;
+                    buf[j++] = buf[i];
+                    s->do_telnetopt++;
+                } else if (s->is_tn3270 && ((unsigned char)buf[i] == IAC_IP
+                           || (unsigned char)buf[i] == IAC_NOP)
+                           && s->do_telnetopt == 2) {
+                    /* TODO: IP and NOP need to be implemented later. */
+                    s->do_telnetopt++;
                 }
                 s->do_telnetopt++;
             }
@@ -512,7 +531,7 @@ static void tcp_chr_update_read_handler(Chardev *chr,
 
 typedef struct {
     Chardev *chr;
-    char buf[12];
+    char buf[21];
     size_t buflen;
 } TCPChardevTelnetInit;
 
@@ -550,9 +569,6 @@ static void tcp_chr_telnet_init(Chardev *chr)
     TCPChardevTelnetInit *init = g_new0(TCPChardevTelnetInit, 1);
     size_t n = 0;
 
-    init->chr = chr;
-    init->buflen = 12;
-
 #define IACSET(x, a, b, c)                      \
     do {                                        \
         x[n++] = a;                             \
@@ -560,12 +576,26 @@ static void tcp_chr_telnet_init(Chardev *chr)
         x[n++] = c;                             \
     } while (0)
 
-    /* Prep the telnet negotion to put telnet in binary,
+    init->chr = chr;
-     * no echo, single char mode */
+    if (!s->is_tn3270) {
-    IACSET(init->buf, 0xff, 0xfb, 0x01);  /* IAC WILL ECHO */
+        init->buflen = 12;
-    IACSET(init->buf, 0xff, 0xfb, 0x03);  /* IAC WILL Suppress go ahead */
+        /* Prep the telnet negotion to put telnet in binary,
-    IACSET(init->buf, 0xff, 0xfb, 0x00);  /* IAC WILL Binary */
+         * no echo, single char mode */
-    IACSET(init->buf, 0xff, 0xfd, 0x00);  /* IAC DO Binary */
+        IACSET(init->buf, 0xff, 0xfb, 0x01);  /* IAC WILL ECHO */
+        IACSET(init->buf, 0xff, 0xfb, 0x03);  /* IAC WILL Suppress go ahead */
+        IACSET(init->buf, 0xff, 0xfb, 0x00);  /* IAC WILL Binary */
+        IACSET(init->buf, 0xff, 0xfd, 0x00);  /* IAC DO Binary */
+    } else {
+        init->buflen = 21;
+        /* Prep the TN3270 negotion based on RFC1576 */
+        IACSET(init->buf, 0xff, 0xfd, 0x19);  /* IAC DO EOR */
+        IACSET(init->buf, 0xff, 0xfb, 0x19);  /* IAC WILL EOR */
+        IACSET(init->buf, 0xff, 0xfd, 0x00);  /* IAC DO BINARY */
+        IACSET(init->buf, 0xff, 0xfb, 0x00);  /* IAC WILL BINARY */
+        IACSET(init->buf, 0xff, 0xfd, 0x18);  /* IAC DO TERMINAL TYPE */
+        IACSET(init->buf, 0xff, 0xfa, 0x18);  /* IAC SB TERMINAL TYPE */
+        IACSET(init->buf, 0x01, 0xff, 0xf0);  /* SEND IAC SE */
+    }
 
 #undef IACSET
 
@@ -585,7 +615,8 @@ static void tcp_chr_tls_handshake(QIOTask *task,
     if (qio_task_propagate_error(task, NULL)) {
         tcp_chr_disconnect(chr);
     } else {
-        if (s->do_telnetopt) {
+        /* tn3270 does not support TLS yet */
+        if (s->do_telnetopt && !s->is_tn3270) {
             tcp_chr_telnet_init(chr);
         } else {
             tcp_chr_connect(chr);
@@ -824,12 +855,14 @@ static void qmp_chardev_open_socket(Chardev *chr,
     bool do_nodelay     = sock->has_nodelay ? sock->nodelay : false;
     bool is_listen      = sock->has_server  ? sock->server  : true;
     bool is_telnet      = sock->has_telnet  ? sock->telnet  : false;
+    bool is_tn3270      = sock->has_tn3270  ? sock->tn3270  : false;
     bool is_waitconnect = sock->has_wait    ? sock->wait    : false;
     int64_t reconnect   = sock->has_reconnect ? sock->reconnect : 0;
     QIOChannelSocket *sioc = NULL;
 
     s->is_listen = is_listen;
     s->is_telnet = is_telnet;
+    s->is_tn3270 = is_tn3270;
     s->do_nodelay = do_nodelay;
     if (sock->tls_creds) {
         Object *creds;
@@ -879,7 +912,7 @@ static void qmp_chardev_open_socket(Chardev *chr,
                                          addr, is_listen, is_telnet);
 
     if (is_listen) {
-        if (is_telnet) {
+        if (is_telnet || is_tn3270) {
             s->do_telnetopt = 1;
         }
     } else if (reconnect > 0) {
@@ -933,6 +966,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     bool is_listen      = qemu_opt_get_bool(opts, "server", false);
     bool is_waitconnect = is_listen && qemu_opt_get_bool(opts, "wait", true);
     bool is_telnet      = qemu_opt_get_bool(opts, "telnet", false);
+    bool is_tn3270      = qemu_opt_get_bool(opts, "tn3270", false);
     bool do_nodelay     = !qemu_opt_get_bool(opts, "delay", true);
     int64_t reconnect   = qemu_opt_get_number(opts, "reconnect", 0);
     const char *path = qemu_opt_get(opts, "path");
@@ -968,6 +1002,8 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     sock->server = is_listen;
     sock->has_telnet = true;
     sock->telnet = is_telnet;
+    sock->has_tn3270 = true;
+    sock->tn3270 = is_tn3270;
     sock->has_wait = true;
     sock->wait = is_waitconnect;
     sock->has_reconnect = true;

chardev/char.c

@@ -696,7 +696,8 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
         return opts;
     }
     if (strstart(filename, "tcp:", &p) ||
-        strstart(filename, "telnet:", &p)) {
+        strstart(filename, "telnet:", &p) ||
+        strstart(filename, "tn3270:", &p)) {
         if (sscanf(p, "%64[^:]:%32[^,]%n", host, port, &pos) < 2) {
             host[0] = 0;
             if (sscanf(p, ":%32[^,]%n", port, &pos) < 1)
@@ -712,8 +713,11 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
                 goto fail;
             }
         }
-        if (strstart(filename, "telnet:", &p))
+        if (strstart(filename, "telnet:", &p)) {
             qemu_opt_set(opts, "telnet", "on", &error_abort);
+        } else if (strstart(filename, "tn3270:", &p)) {
+            qemu_opt_set(opts, "tn3270", "on", &error_abort);
+        }
         return opts;
     }
     if (strstart(filename, "udp:", &p)) {
@@ -1176,6 +1180,9 @@ QemuOptsList qemu_chardev_opts = {
         },{
             .name = "telnet",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "tn3270",
+            .type = QEMU_OPT_BOOL,
         },{
             .name = "tls-creds",
             .type = QEMU_OPT_STRING,

default-configs/s390x-softmmu.mak

@@ -2,6 +2,7 @@ CONFIG_PCI=y
 CONFIG_VIRTIO_PCI=y
 CONFIG_VIRTIO=y
 CONFIG_SCLPCONSOLE=y
+CONFIG_TERMINAL3270=y
 CONFIG_S390_FLIC=y
 CONFIG_S390_FLIC_KVM=$(CONFIG_KVM)
 CONFIG_WDT_DIAG288=y

hw/char/Makefile.objs

@@ -29,3 +29,4 @@ common-obj-$(CONFIG_MILKYMIST) += milkymist-uart.o
 common-obj-$(CONFIG_SCLPCONSOLE) += sclpconsole.o sclpconsole-lm.o
 
 obj-$(CONFIG_VIRTIO) += virtio-serial-bus.o
+obj-$(CONFIG_TERMINAL3270) += terminal3270.o

hw/char/terminal3270.c

@@ -0,0 +1,293 @@
+/*
+ * Terminal 3270 implementation
+ *
+ * Copyright 2017 IBM Corp.
+ *
+ * Authors: Yang Chen <bjcyang@linux.vnet.ibm.com>
+ *          Jing Liu <liujbjl@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "sysemu/char.h"
+#include "hw/s390x/3270-ccw.h"
+
+/* Enough spaces for different window sizes. */
+#define INPUT_BUFFER_SIZE  1000
+/*
+ * 1 for header, 1024*2 for datastream, 2 for tail
+ * Reserve enough spaces for telnet IAC escape.
+ */
+#define OUTPUT_BUFFER_SIZE 2051
+
+typedef struct Terminal3270 {
+    EmulatedCcw3270Device cdev;
+    CharBackend chr;
+    uint8_t inv[INPUT_BUFFER_SIZE];
+    uint8_t outv[OUTPUT_BUFFER_SIZE];
+    int in_len;
+    int out_len;
+    bool handshake_done;
+    guint timer_tag;
+} Terminal3270;
+
+#define TYPE_TERMINAL_3270 "x-terminal3270"
+#define TERMINAL_3270(obj) \
+        OBJECT_CHECK(Terminal3270, (obj), TYPE_TERMINAL_3270)
+
+static int terminal_can_read(void *opaque)
+{
+    Terminal3270 *t = opaque;
+
+    return INPUT_BUFFER_SIZE - t->in_len;
+}
+
+/*
+ * Protocol handshake done,
+ * signal guest by an unsolicited DE irq.
+ */
+static void TN3270_handshake_done(Terminal3270 *t)
+{
+    CcwDevice *ccw_dev = CCW_DEVICE(t);
+    SubchDev *sch = ccw_dev->sch;
+
+    t->handshake_done = true;
+    sch->curr_status.scsw.dstat = SCSW_DSTAT_DEVICE_END;
+    css_conditional_io_interrupt(sch);
+}
+
+/*
+ * Called when the interval is timeout to detect
+ * if the client is still alive by Timing Mark.
+ */
+static gboolean send_timing_mark_cb(gpointer opaque)
+{
+    Terminal3270 *t = opaque;
+    const uint8_t timing[] = {0xff, 0xfd, 0x06};
+
+    qemu_chr_fe_write_all(&t->chr, timing, sizeof(timing));
+    return true;
+}
+
+/*
+ * Receive inbound data from socket.
+ * For data given to guest, drop the data boundary IAC, IAC_EOR.
+ * TODO:
+ * Using "Reset" key on x3270 may result multiple commands in one packet.
+ * This usually happens when the user meets a poor traffic of the network.
+ * As of now, for such case, we simply terminate the connection,
+ * and we should come back here later with a better solution.
+ */
+static void terminal_read(void *opaque, const uint8_t *buf, int size)
+{
+    Terminal3270 *t = opaque;
+    CcwDevice *ccw_dev = CCW_DEVICE(t);
+    SubchDev *sch = ccw_dev->sch;
+    int end;
+
+    assert(size <= (INPUT_BUFFER_SIZE - t->in_len));
+
+    if (t->timer_tag) {
+        g_source_remove(t->timer_tag);
+        t->timer_tag = 0;
+    }
+    t->timer_tag = g_timeout_add_seconds(600, send_timing_mark_cb, t);
+
+    memcpy(&t->inv[t->in_len], buf, size);
+    t->in_len += size;
+    if (t->in_len < 2) {
+        return;
+    }
+
+    if (!t->handshake_done) {
+        /*
+         * Receiving Terminal Type is the last step of handshake.
+         * The data format: IAC SB Terminal-Type IS <terminal type> IAC SE
+         * The code for Terminal-Type is 0x18, for IS is 0.
+         * Simply check the data format and mark handshake_done.
+         */
+        if (t->in_len > 6 && t->inv[2] == 0x18 && t->inv[3] == 0x0 &&
+            t->inv[t->in_len - 2] == IAC && t->inv[t->in_len - 1] == IAC_SE) {
+            TN3270_handshake_done(t);
+            t->in_len = 0;
+        }
+        return;
+    }
+
+    for (end = 0; end < t->in_len - 1; end++) {
+        if (t->inv[end] == IAC && t->inv[end + 1] == IAC_EOR) {
+            break;
+        }
+    }
+    if (end == t->in_len - 2) {
+        /* Data is valid for consuming. */
+        t->in_len -= 2;
+        sch->curr_status.scsw.dstat = SCSW_DSTAT_ATTENTION;
+        css_conditional_io_interrupt(sch);
+    } else if (end < t->in_len - 2) {
+        /* "Reset" key is used. */
+        qemu_chr_fe_disconnect(&t->chr);
+    } else {
+        /* Gathering data. */
+        return;
+    }
+}
+
+static void chr_event(void *opaque, int event)
+{
+    Terminal3270 *t = opaque;
+    CcwDevice *ccw_dev = CCW_DEVICE(t);
+    SubchDev *sch = ccw_dev->sch;
+
+    /* Ensure the initial status correct, always reset them. */
+    t->in_len = 0;
+    t->out_len = 0;
+    t->handshake_done = false;
+    if (t->timer_tag) {
+        g_source_remove(t->timer_tag);
+        t->timer_tag = 0;
+    }
+
+    switch (event) {
+    case CHR_EVENT_OPENED:
+        /*
+         * 3270 does handshake firstly by the negotiate options in
+         * char-socket.c. Once qemu receives the terminal-type of the
+         * client, mark handshake done and trigger everything rolling again.
+         */
+        t->timer_tag = g_timeout_add_seconds(600, send_timing_mark_cb, t);
+        break;
+    case CHR_EVENT_CLOSED:
+        sch->curr_status.scsw.dstat = SCSW_DSTAT_DEVICE_END;
+        css_conditional_io_interrupt(sch);
+        break;
+    }
+}
+
+static void terminal_init(EmulatedCcw3270Device *dev, Error **errp)
+{
+    Terminal3270 *t = TERMINAL_3270(dev);
+    static bool terminal_available;
+
+    if (terminal_available) {
+        error_setg(errp, "Multiple 3270 terminals are not supported.");
+        return;
+    }
+    terminal_available = true;
+    qemu_chr_fe_set_handlers(&t->chr, terminal_can_read,
+                             terminal_read, chr_event, t, NULL, true);
+}
+
+static int read_payload_3270(EmulatedCcw3270Device *dev, uint32_t cda,
+                             uint16_t count)
+{
+    Terminal3270 *t = TERMINAL_3270(dev);
+    int len;
+
+    len = MIN(count, t->in_len);
+    cpu_physical_memory_write(cda, t->inv, len);
+    t->in_len -= len;
+
+    return len;
+}
+
+/* TN3270 uses binary transmission, which needs escape IAC to IAC IAC */
+static int insert_IAC_escape_char(uint8_t *outv, int out_len)
+{
+    int IAC_num = 0, new_out_len, i, j;
+
+    for (i = 0; i < out_len; i++) {
+        if (outv[i] == IAC) {
+            IAC_num++;
+        }
+    }
+    if (IAC_num == 0) {
+        return out_len;
+    }
+    new_out_len = out_len + IAC_num;
+    for (i = out_len - 1, j = new_out_len - 1; j > i && i >= 0; i--, j--) {
+        outv[j] = outv[i];
+        if (outv[i] == IAC) {
+            outv[--j] = IAC;
+        }
+    }
+    return new_out_len;
+}
+
+/*
+ * Write 3270 outbound to socket.
+ * Return the count of 3270 data field if succeeded, zero if failed.
+ */
+static int write_payload_3270(EmulatedCcw3270Device *dev, uint8_t cmd,
+                              uint32_t cda, uint16_t count)
+{
+    Terminal3270 *t = TERMINAL_3270(dev);
+    int retval = 0;
+
+    assert(count <= (OUTPUT_BUFFER_SIZE - 3) / 2);
+
+    if (!t->handshake_done) {
+        if (!(t->outv[0] == IAC && t->outv[1] != IAC)) {
+            /*
+             * Before having finished 3270 negotiation,
+             * sending outbound data except protocol options is prohibited.
+             */
+            return 0;
+        }
+    }
+    if (!qemu_chr_fe_get_driver(&t->chr)) {
+        /* We just say we consumed all data if there's no backend. */
+        return count;
+    }
+    t->outv[0] = cmd;
+    cpu_physical_memory_read(cda, &t->outv[1], count);
+    t->out_len = count + 1;
+
+    t->out_len = insert_IAC_escape_char(t->outv, t->out_len);
+    t->outv[t->out_len++] = IAC;
+    t->outv[t->out_len++] = IAC_EOR;
+
+    retval = qemu_chr_fe_write_all(&t->chr, t->outv, t->out_len);
+    return (retval <= 0) ? 0 : (retval - 3);
+}
+
+static Property terminal_properties[] = {
+    DEFINE_PROP_CHR("chardev", Terminal3270, chr),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static const VMStateDescription terminal3270_vmstate = {
+    .name = TYPE_TERMINAL_3270,
+    .unmigratable = 1,
+};
+
+static void terminal_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    EmulatedCcw3270Class *ck = EMULATED_CCW_3270_CLASS(klass);
+
+    dc->props = terminal_properties;
+    dc->vmsd = &terminal3270_vmstate;
+    ck->init = terminal_init;
+    ck->read_payload_3270 = read_payload_3270;
+    ck->write_payload_3270 = write_payload_3270;
+}
+
+static const TypeInfo ccw_terminal_info = {
+    .name = TYPE_TERMINAL_3270,
+    .parent = TYPE_EMULATED_CCW_3270,
+    .instance_size = sizeof(Terminal3270),
+    .class_init = terminal_class_init,
+    .class_size = sizeof(EmulatedCcw3270Class),
+};
+
+static void register_types(void)
+{
+    type_register_static(&ccw_terminal_info);
+}
+
+type_init(register_types)

hw/s390x/3270-ccw.c

@@ -0,0 +1,174 @@
+/*
+ * Emulated ccw-attached 3270 implementation
+ *
+ * Copyright 2017 IBM Corp.
+ * Author(s): Yang Chen <bjcyang@linux.vnet.ibm.com>
+ *            Jing Liu <liujbjl@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/module.h"
+#include "cpu.h"
+#include "hw/s390x/css.h"
+#include "hw/s390x/css-bridge.h"
+#include "hw/s390x/3270-ccw.h"
+
+/* Handle READ ccw commands from guest */
+static int handle_payload_3270_read(EmulatedCcw3270Device *dev, CCW1 *ccw)
+{
+    EmulatedCcw3270Class *ck = EMULATED_CCW_3270_GET_CLASS(dev);
+    CcwDevice *ccw_dev = CCW_DEVICE(dev);
+    int len;
+
+    if (!ccw->cda) {
+        return -EFAULT;
+    }
+
+    len = ck->read_payload_3270(dev, ccw->cda, ccw->count);
+    ccw_dev->sch->curr_status.scsw.count = ccw->count - len;
+
+    return 0;
+}
+
+/* Handle WRITE ccw commands to write data to client */
+static int handle_payload_3270_write(EmulatedCcw3270Device *dev, CCW1 *ccw)
+{
+    EmulatedCcw3270Class *ck = EMULATED_CCW_3270_GET_CLASS(dev);
+    CcwDevice *ccw_dev = CCW_DEVICE(dev);
+    int len;
+
+    if (!ccw->cda) {
+        return -EFAULT;
+    }
+
+    len = ck->write_payload_3270(dev, ccw->cmd_code, ccw->cda, ccw->count);
+
+    if (len <= 0) {
+        return -EIO;
+    }
+
+    ccw_dev->sch->curr_status.scsw.count = ccw->count - len;
+    return 0;
+}
+
+static int emulated_ccw_3270_cb(SubchDev *sch, CCW1 ccw)
+{
+    int rc = 0;
+    EmulatedCcw3270Device *dev = sch->driver_data;
+
+    switch (ccw.cmd_code) {
+    case TC_WRITESF:
+    case TC_WRITE:
+    case TC_EWRITE:
+    case TC_EWRITEA:
+        rc = handle_payload_3270_write(dev, &ccw);
+        break;
+    case TC_RDBUF:
+    case TC_READMOD:
+        rc = handle_payload_3270_read(dev, &ccw);
+        break;
+    default:
+        rc = -ENOSYS;
+        break;
+    }
+
+    if (rc == -EIO) {
+        /* I/O error, specific devices generate specific conditions */
+        SCSW *s = &sch->curr_status.scsw;
+
+        sch->curr_status.scsw.dstat = SCSW_DSTAT_UNIT_CHECK;
+        sch->sense_data[0] = 0x40;    /* intervention-req */
+        s->ctrl &= ~SCSW_ACTL_START_PEND;
+        s->ctrl &= ~SCSW_CTRL_MASK_STCTL;
+        s->ctrl |= SCSW_STCTL_PRIMARY | SCSW_STCTL_SECONDARY |
+                   SCSW_STCTL_ALERT | SCSW_STCTL_STATUS_PEND;
+    }
+
+    return rc;
+}
+
+static void emulated_ccw_3270_realize(DeviceState *ds, Error **errp)
+{
+    uint16_t chpid;
+    EmulatedCcw3270Device *dev = EMULATED_CCW_3270(ds);
+    EmulatedCcw3270Class *ck = EMULATED_CCW_3270_GET_CLASS(dev);
+    CcwDevice *cdev = CCW_DEVICE(ds);
+    CCWDeviceClass *cdk = CCW_DEVICE_GET_CLASS(cdev);
+    SubchDev *sch = css_create_virtual_sch(cdev->devno, errp);
+    Error *err = NULL;
+
+    if (!sch) {
+        return;
+    }
+
+    if (!ck->init) {
+        goto out_err;
+    }
+
+    sch->driver_data = dev;
+    cdev->sch = sch;
+    chpid = css_find_free_chpid(sch->cssid);
+
+    if (chpid > MAX_CHPID) {
+        error_setg(&err, "No available chpid to use.");
+        goto out_err;
+    }
+
+    sch->id.reserved = 0xff;
+    sch->id.cu_type = EMULATED_CCW_3270_CU_TYPE;
+    css_sch_build_virtual_schib(sch, (uint8_t)chpid,
+                                EMULATED_CCW_3270_CHPID_TYPE);
+    sch->ccw_cb = emulated_ccw_3270_cb;
+
+    ck->init(dev, &err);
+    if (err) {
+        goto out_err;
+    }
+
+    cdk->realize(cdev, &err);
+    if (err) {
+        goto out_err;
+    }
+
+    return;
+
+out_err:
+    error_propagate(errp, err);
+    css_subch_assign(sch->cssid, sch->ssid, sch->schid, sch->devno, NULL);
+    cdev->sch = NULL;
+    g_free(sch);
+}
+
+static Property emulated_ccw_3270_properties[] = {
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void emulated_ccw_3270_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->props = emulated_ccw_3270_properties;
+    dc->bus_type = TYPE_VIRTUAL_CSS_BUS;
+    dc->realize = emulated_ccw_3270_realize;
+    dc->hotpluggable = false;
+}
+
+static const TypeInfo emulated_ccw_3270_info = {
+    .name = TYPE_EMULATED_CCW_3270,
+    .parent = TYPE_CCW_DEVICE,
+    .instance_size = sizeof(EmulatedCcw3270Device),
+    .class_init = emulated_ccw_3270_class_init,
+    .class_size = sizeof(EmulatedCcw3270Class),
+    .abstract = true,
+};
+
+static void emulated_ccw_register(void)
+{
+    type_register_static(&emulated_ccw_3270_info);
+}
+
+type_init(emulated_ccw_register)

hw/s390x/Makefile.objs

@@ -7,6 +7,7 @@ obj-y += sclpcpu.o
 obj-y += ipl.o
 obj-y += css.o
 obj-y += s390-virtio-ccw.o
+obj-y += 3270-ccw.o
 obj-y += virtio-ccw.o
 obj-y += css-bridge.o
 obj-y += ccw-device.o

hw/s390x/css.c

@@ -576,6 +576,9 @@ static void sch_handle_start_func(SubchDev *sch, ORB *orb)
             s->dstat = SCSW_DSTAT_CHANNEL_END | SCSW_DSTAT_DEVICE_END;
             s->cpa = sch->channel_prog + 8;
             break;
+        case -EIO:
+            /* I/O errors, status depends on specific devices */
+            break;
         case -ENOSYS:
             /* unsupported command, generate unit check (command reject) */
             s->ctrl &= ~SCSW_ACTL_START_PEND;
@@ -1302,6 +1305,27 @@ bool css_schid_final(int m, uint8_t cssid, uint8_t ssid, uint16_t schid)
                                  (MAX_SCHID + 1) / sizeof(unsigned long));
 }
 
+unsigned int css_find_free_chpid(uint8_t cssid)
+{
+    CssImage *css = channel_subsys.css[cssid];
+    unsigned int chpid;
+
+    if (!css) {
+        return MAX_CHPID + 1;
+    }
+
+    for (chpid = 0; chpid <= MAX_CHPID; chpid++) {
+        /* skip reserved chpid */
+        if (chpid == VIRTIO_CCW_CHPID) {
+            continue;
+        }
+        if (!css->chpids[chpid].in_use) {
+            return chpid;
+        }
+    }
+    return MAX_CHPID + 1;
+}
+
 static int css_add_virtual_chpid(uint8_t cssid, uint8_t chpid, uint8_t type)
 {
     CssImage *css;

include/hw/s390x/3270-ccw.h

@@ -0,0 +1,53 @@
+/*
+ * Emulated ccw-attached 3270 definitions
+ *
+ * Copyright 2017 IBM Corp.
+ * Author(s): Yang Chen <bjcyang@linux.vnet.ibm.com>
+ *            Jing Liu <liujbjl@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#ifndef HW_S390X_3270_CCW_H
+#define HW_S390X_3270_CCW_H
+
+#include "hw/sysbus.h"
+#include "hw/s390x/css.h"
+#include "hw/s390x/ccw-device.h"
+
+#define EMULATED_CCW_3270_CU_TYPE 0x3270
+#define EMULATED_CCW_3270_CHPID_TYPE 0x1a
+
+#define TYPE_EMULATED_CCW_3270 "emulated-ccw-3270"
+
+/* Local Channel Commands */
+#define TC_WRITE   0x01         /* Write */
+#define TC_RDBUF   0x02         /* Read buffer */
+#define TC_EWRITE  0x05         /* Erase write */
+#define TC_READMOD 0x06         /* Read modified */
+#define TC_EWRITEA 0x0d         /* Erase write alternate */
+#define TC_WRITESF 0x11         /* Write structured field */
+
+#define EMULATED_CCW_3270(obj) \
+     OBJECT_CHECK(EmulatedCcw3270Device, (obj), TYPE_EMULATED_CCW_3270)
+#define EMULATED_CCW_3270_CLASS(klass) \
+     OBJECT_CLASS_CHECK(EmulatedCcw3270Class, (klass), TYPE_EMULATED_CCW_3270)
+#define EMULATED_CCW_3270_GET_CLASS(obj) \
+     OBJECT_GET_CLASS(EmulatedCcw3270Class, (obj), TYPE_EMULATED_CCW_3270)
+
+typedef struct EmulatedCcw3270Device {
+    CcwDevice parent_obj;
+} EmulatedCcw3270Device;
+
+typedef struct EmulatedCcw3270Class {
+    CCWDeviceClass parent_class;
+
+    void (*init)(EmulatedCcw3270Device *, Error **);
+    int (*read_payload_3270)(EmulatedCcw3270Device *, uint32_t, uint16_t);
+    int (*write_payload_3270)(EmulatedCcw3270Device *, uint8_t, uint32_t,
+                              uint16_t);
+} EmulatedCcw3270Class;
+
+#endif

include/hw/s390x/css.h

@@ -28,6 +28,7 @@
 #define MAX_CIWS 62
 
 #define VIRTUAL_CSSID 0xfe
+#define VIRTIO_CCW_CHPID 0   /* used by convention */
 
 typedef struct CIW {
     uint8_t type;
@@ -115,6 +116,7 @@ bool css_devno_used(uint8_t cssid, uint8_t ssid, uint16_t devno);
 void css_subch_assign(uint8_t cssid, uint8_t ssid, uint16_t schid,
                       uint16_t devno, SubchDev *sch);
 void css_sch_build_virtual_schib(SubchDev *sch, uint8_t chpid, uint8_t type);
+unsigned int css_find_free_chpid(uint8_t cssid);
 uint16_t css_build_subchannel_id(SubchDev *sch);
 void css_reset(void);
 void css_reset_sch(SubchDev *sch);

include/sysemu/char.h

@@ -7,6 +7,14 @@
 #include "qemu/bitmap.h"
 #include "qom/object.h"
 
+#define IAC_EOR 239
+#define IAC_SE 240
+#define IAC_NOP 241
+#define IAC_BREAK 243
+#define IAC_IP 244
+#define IAC_SB 250
+#define IAC 255
+
 /* character device */
 
 typedef enum {

qapi-schema.json

@@ -4877,6 +4877,8 @@
 # @nodelay: set TCP_NODELAY socket option (default: false)
 # @telnet: enable telnet protocol on server
 #          sockets (default: false)
+# @tn3270: enable tn3270 protocol on server
+#          sockets (default: false) (Since: 2.10)
 # @reconnect: For a client socket, if a socket is disconnected,
 #          then attempt a reconnect after the given number of seconds.
 #          Setting this to zero disables this function. (default: 0)
@@ -4890,6 +4892,7 @@
                                      '*wait'      : 'bool',
                                      '*nodelay'   : 'bool',
                                      '*telnet'    : 'bool',
+                                     '*tn3270'    : 'bool',
                                      '*reconnect' : 'int' },
   'base': 'ChardevCommon' }