[Qemu-devel] [PATCH v5 1/7] replay: character devices

[Pavel Dovgalyuk]

This patch implements record and replay of character devices.
It records chardevs communication in replay mode. Recorded information
include data read from backend and counter of bytes written
from frontend to backend to preserve frontend internal state.
If character device was configured through the command line in record mode,
then in replay mode it should be also added to command line. Backend of
the character device could be changed in replay mode.
Replaying of devices that perform ioctl and get_msgfd operations is not
supported.
gdbstub which also acts as a backend is not recorded to allow controlling
the replaying through gdb. Monitor backends are also not recorded.

Signed-off-by: Pavel Dovgalyuk <address@hidden>
---
 gdbstub.c                |    2 -
 include/sysemu/char.h    |   26 +++++++
 include/sysemu/replay.h  |   17 +++++
 qemu-char.c              |  138 +++++++++++++++++++++++++++++++-------
 replay/Makefile.objs     |    1 
 replay/replay-char.c     |  167 ++++++++++++++++++++++++++++++++++++++++++++++
 replay/replay-events.c   |   17 ++++-
 replay/replay-internal.h |   18 +++++
 replay/replay.c          |    2 -
 9 files changed, 358 insertions(+), 30 deletions(-)
 create mode 100755 replay/replay-char.c

diff --git a/gdbstub.c b/gdbstub.c
index 61c12b1..fdcb0ee 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1752,7 +1752,7 @@ int gdbserver_start(const char *device)
             sigaction(SIGINT, &act, NULL);
         }
 #endif
-        chr = qemu_chr_new("gdb", device, NULL);
+        chr = qemu_chr_new_noreplay("gdb", device, NULL);
         if (!chr)
             return -1;
 
diff --git a/include/sysemu/char.h b/include/sysemu/char.h
index e46884f..4c2f777 100644
--- a/include/sysemu/char.h
+++ b/include/sysemu/char.h
@@ -86,6 +86,7 @@ struct CharDriverState {
     int is_mux;
     guint fd_in_tag;
     QemuOpts *opts;
+    bool replay;
     QTAILQ_ENTRY(CharDriverState) next;
 };
 
@@ -139,6 +140,22 @@ CharDriverState *qemu_chr_new(const char *label, const 
char *filename,
                               void (*init)(struct CharDriverState *s));
 
 /**
+ * @qemu_chr_new_noreplay:
+ *
+ * Create a new character backend from a URI.
+ * Character device communications are not written
+ * into the replay log.
+ *
+ * @label the name of the backend
+ * @filename the URI
+ * @init not sure..
+ *
+ * Returns: a new character backend
+ */
+CharDriverState *qemu_chr_new_noreplay(const char *label, const char *filename,
+                                       void (*init)(struct CharDriverState 
*s));
+
+/**
  * @qemu_chr_delete:
  *
  * Destroy a character backend and remove it from the list of
@@ -341,6 +358,15 @@ int qemu_chr_be_can_write(CharDriverState *s);
  */
 void qemu_chr_be_write(CharDriverState *s, uint8_t *buf, int len);
 
+/**
+ * @qemu_chr_be_write_impl:
+ *
+ * Implementation of back end writing. Used by replay module.
+ *
+ * @buf a buffer to receive data from the front end
+ * @len the number of bytes to receive from the front end
+ */
+void qemu_chr_be_write_impl(CharDriverState *s, uint8_t *buf, int len);
 
 /**
  * @qemu_chr_be_event:
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index e4108e8..d24d502 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -114,4 +114,21 @@ void replay_input_event(QemuConsole *src, InputEvent *evt);
 /*! Adds input sync event to the queue */
 void replay_input_sync_event(void);
 
+/* Character device */
+
+/*! Registers char driver to save it's events */
+void replay_register_char_driver(struct CharDriverState *chr);
+/*! Saves write to char device event to the log */
+void replay_chr_be_write(struct CharDriverState *s, uint8_t *buf, int len);
+/*! Writes char write return value to the replay log. */
+void replay_char_write_event_save(int res, int offset);
+/*! Reads char write return value from the replay log. */
+void replay_char_write_event_load(int *res, int *offset);
+/*! Reads information about read_all character event. */
+int replay_char_read_all_load(uint8_t *buf);
+/*! Writes character read_all error code into the replay log. */
+void replay_char_read_all_save_error(int res);
+/*! Writes character read_all execution result into the replay log. */
+void replay_char_read_all_save_buf(uint8_t *buf, int offset);
+
 #endif
diff --git a/qemu-char.c b/qemu-char.c
index e0147f3..b418307 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -37,6 +37,7 @@
 #include "io/channel-socket.h"
 #include "io/channel-file.h"
 #include "io/channel-tls.h"
+#include "sysemu/replay.h"
 
 #include <zlib.h>
 
@@ -234,10 +235,46 @@ static void qemu_chr_fe_write_log(CharDriverState *s,
     }
 }
 
+static int qemu_chr_fe_write_buffer(CharDriverState *s, const uint8_t *buf, 
int len, int *offset)
+{
+    int res = 0;
+    *offset = 0;
+
+    qemu_mutex_lock(&s->chr_write_lock);
+    while (*offset < len) {
+        do {
+            res = s->chr_write(s, buf + *offset, len - *offset);
+            if (res == -1 && errno == EAGAIN) {
+                g_usleep(100);
+            }
+        } while (res == -1 && errno == EAGAIN);
+
+        if (res <= 0) {
+            break;
+        }
+
+        *offset += res;
+    }
+    if (*offset > 0) {
+        qemu_chr_fe_write_log(s, buf, *offset);
+    }
+    qemu_mutex_unlock(&s->chr_write_lock);
+
+    return res;
+}
+
 int qemu_chr_fe_write(CharDriverState *s, const uint8_t *buf, int len)
 {
     int ret;
 
+    if (s->replay && replay_mode == REPLAY_MODE_PLAY) {
+        int offset;
+        replay_char_write_event_load(&ret, &offset);
+        assert(offset <= len);
+        qemu_chr_fe_write_buffer(s, buf, offset, &offset);
+        return ret;
+    }
+
     qemu_mutex_lock(&s->chr_write_lock);
     ret = s->chr_write(s, buf, len);
 
@@ -246,34 +283,31 @@ int qemu_chr_fe_write(CharDriverState *s, const uint8_t 
*buf, int len)
     }
 
     qemu_mutex_unlock(&s->chr_write_lock);
+    
+    if (s->replay && replay_mode == REPLAY_MODE_RECORD) {
+        replay_char_write_event_save(ret, ret < 0 ? 0 : ret);
+    }
+    
     return ret;
 }
 
 int qemu_chr_fe_write_all(CharDriverState *s, const uint8_t *buf, int len)
 {
-    int offset = 0;
-    int res = 0;
+    int offset;
+    int res;
 
-    qemu_mutex_lock(&s->chr_write_lock);
-    while (offset < len) {
-        do {
-            res = s->chr_write(s, buf + offset, len - offset);
-            if (res == -1 && errno == EAGAIN) {
-                g_usleep(100);
-            }
-        } while (res == -1 && errno == EAGAIN);
+    if (s->replay && replay_mode == REPLAY_MODE_PLAY) {
+        replay_char_write_event_load(&res, &offset);
+        assert(offset <= len);
+        qemu_chr_fe_write_buffer(s, buf, offset, &offset);
+        return res;
+    }
 
-        if (res <= 0) {
-            break;
-        }
+    res = qemu_chr_fe_write_buffer(s, buf, len, &offset);
 
-        offset += res;
+    if (s->replay && replay_mode == REPLAY_MODE_RECORD) {
+        replay_char_write_event_save(res, offset);
     }
-    if (offset > 0) {
-        qemu_chr_fe_write_log(s, buf, offset);
-    }
-
-    qemu_mutex_unlock(&s->chr_write_lock);
 
     if (res < 0) {
         return res;
@@ -289,6 +323,10 @@ int qemu_chr_fe_read_all(CharDriverState *s, uint8_t *buf, 
int len)
     if (!s->chr_sync_read) {
         return 0;
     }
+    
+    if (s->replay && replay_mode == REPLAY_MODE_PLAY) {
+        return replay_char_read_all_load(buf);
+    }
 
     while (offset < len) {
         do {
@@ -303,6 +341,9 @@ int qemu_chr_fe_read_all(CharDriverState *s, uint8_t *buf, 
int len)
         }
 
         if (res < 0) {
+            if (s->replay && replay_mode == REPLAY_MODE_RECORD) {
+                replay_char_read_all_save_error(res);
+            }
             return res;
         }
 
@@ -313,14 +354,22 @@ int qemu_chr_fe_read_all(CharDriverState *s, uint8_t 
*buf, int len)
         }
     }
 
+    if (s->replay && replay_mode == REPLAY_MODE_RECORD) {
+        replay_char_read_all_save_buf(buf, offset);
+    }
     return offset;
 }
 
 int qemu_chr_fe_ioctl(CharDriverState *s, int cmd, void *arg)
 {
-    if (!s->chr_ioctl)
-        return -ENOTSUP;
-    return s->chr_ioctl(s, cmd, arg);
+    int res;
+    if (!s->chr_ioctl || s->replay) {
+        res = -ENOTSUP;
+    } else {
+        res = s->chr_ioctl(s, cmd, arg);
+    }
+
+    return res;
 }
 
 int qemu_chr_be_can_write(CharDriverState *s)
@@ -330,17 +379,35 @@ int qemu_chr_be_can_write(CharDriverState *s)
     return s->chr_can_read(s->handler_opaque);
 }
 
-void qemu_chr_be_write(CharDriverState *s, uint8_t *buf, int len)
+void qemu_chr_be_write_impl(CharDriverState *s, uint8_t *buf, int len)
 {
     if (s->chr_read) {
         s->chr_read(s->handler_opaque, buf, len);
     }
 }
 
+void qemu_chr_be_write(CharDriverState *s, uint8_t *buf, int len)
+{
+    if (s->replay) {
+        if (replay_mode == REPLAY_MODE_PLAY) {
+            return;
+        }
+        replay_chr_be_write(s, buf, len);
+    } else {
+        qemu_chr_be_write_impl(s, buf, len);
+    }
+}
+
 int qemu_chr_fe_get_msgfd(CharDriverState *s)
 {
     int fd;
-    return (qemu_chr_fe_get_msgfds(s, &fd, 1) == 1) ? fd : -1;
+    int res = (qemu_chr_fe_get_msgfds(s, &fd, 1) == 1) ? fd : -1;
+    if (s->replay) {
+        fprintf(stderr,
+                "Replay: get msgfd is not supported for serial devices yet\n");
+        exit(1);
+    }
+    return res;
 }
 
 int qemu_chr_fe_get_msgfds(CharDriverState *s, int *fds, int len)
@@ -3855,7 +3922,8 @@ err:
     return NULL;
 }
 
-CharDriverState *qemu_chr_new(const char *label, const char *filename, void 
(*init)(struct CharDriverState *s))
+CharDriverState *qemu_chr_new_noreplay(const char *label, const char *filename,
+                                       void (*init)(struct CharDriverState *s))
 {
     const char *p;
     CharDriverState *chr;
@@ -3881,6 +3949,21 @@ CharDriverState *qemu_chr_new(const char *label, const 
char *filename, void (*in
     return chr;
 }
 
+CharDriverState *qemu_chr_new(const char *label, const char *filename, void 
(*init)(struct CharDriverState *s))
+{
+    CharDriverState *chr;
+    chr = qemu_chr_new_noreplay(label, filename, init);
+    if (chr) {
+        chr->replay = replay_mode != REPLAY_MODE_NONE;
+        if (chr->replay && chr->chr_ioctl) {
+            fprintf(stderr,
+                    "Replay: ioctl is not supported for serial devices yet\n");
+        }
+        replay_register_char_driver(chr);
+    }
+    return chr;
+}
+
 void qemu_chr_fe_set_echo(struct CharDriverState *chr, bool echo)
 {
     if (chr->chr_set_echo) {
@@ -4475,6 +4558,11 @@ void qmp_chardev_remove(const char *id, Error **errp)
         error_setg(errp, "Chardev '%s' is busy", id);
         return;
     }
+    if (chr->replay) {
+        error_setg(errp,
+            "Chardev '%s' cannot be unplugged in record/replay mode", id);
+        return;
+    }
     qemu_chr_delete(chr);
 }
 
diff --git a/replay/Makefile.objs b/replay/Makefile.objs
index 232193a..70e5572 100644
--- a/replay/Makefile.objs
+++ b/replay/Makefile.objs
@@ -3,3 +3,4 @@ common-obj-y += replay-internal.o
 common-obj-y += replay-events.o
 common-obj-y += replay-time.o
 common-obj-y += replay-input.o
+common-obj-y += replay-char.o
diff --git a/replay/replay-char.c b/replay/replay-char.c
new file mode 100755
index 0000000..bfbaf2e
--- /dev/null
+++ b/replay/replay-char.c
@@ -0,0 +1,167 @@
+/*
+ * replay-char.c
+ *
+ * Copyright (c) 2010-2016 Institute for System Programming
+ *                         of the Russian Academy of Sciences.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "qemu/osdep.h"
+#include "sysemu/replay.h"
+#include "replay-internal.h"
+#include "sysemu/sysemu.h"
+#include "sysemu/char.h"
+
+/* Char drivers that generate qemu_chr_be_write events
+   that should be saved into the log. */
+static CharDriverState **char_drivers;
+static int drivers_count;
+
+/* Char event attributes. */
+typedef struct CharEvent {
+    int id;
+    uint8_t *buf;
+    size_t len;
+} CharEvent;
+
+static int find_char_driver(CharDriverState *chr)
+{
+    int i = 0;
+    for ( ; i < drivers_count ; ++i) {
+        if (char_drivers[i] == chr) {
+            return i;
+        }
+    }
+    return -1;
+}
+
+void replay_register_char_driver(CharDriverState *chr)
+{
+    if (replay_mode == REPLAY_MODE_NONE) {
+        return;
+    }
+    char_drivers = g_realloc(char_drivers,
+                             sizeof(*char_drivers) * (drivers_count + 1));
+    char_drivers[drivers_count++] = chr;
+}
+
+void replay_chr_be_write(CharDriverState *s, uint8_t *buf, int len)
+{
+    CharEvent *event = g_malloc0(sizeof(CharEvent));
+
+    event->id = find_char_driver(s);
+    if (event->id < 0) {
+        fprintf(stderr, "Replay: cannot find char driver\n");
+        exit(1);
+    }
+    event->buf = g_malloc(len);
+    memcpy(event->buf, buf, len);
+    event->len = len;
+
+    replay_add_event(REPLAY_ASYNC_EVENT_CHAR_READ, event, NULL, 0);
+}
+
+void replay_event_char_read_run(void *opaque)
+{
+    CharEvent *event = (CharEvent *)opaque;
+
+    qemu_chr_be_write_impl(char_drivers[event->id], event->buf,
+                           (int)event->len);
+
+    g_free(event->buf);
+    g_free(event);
+}
+
+void replay_event_char_read_save(void *opaque)
+{
+    CharEvent *event = (CharEvent *)opaque;
+
+    replay_put_byte(event->id);
+    replay_put_array(event->buf, event->len);
+}
+
+void *replay_event_char_read_load(void)
+{
+    CharEvent *event = g_malloc0(sizeof(CharEvent));
+
+    event->id = replay_get_byte();
+    replay_get_array_alloc(&event->buf, &event->len);
+
+    return event;
+}
+
+void replay_char_write_event_save(int res, int offset)
+{
+    replay_save_instructions();
+    replay_mutex_lock();
+    replay_put_event(EVENT_CHAR_WRITE);
+    replay_put_dword(res);
+    replay_put_dword(offset);
+    replay_mutex_unlock();
+}
+
+void replay_char_write_event_load(int *res, int *offset)
+{
+    replay_account_executed_instructions();
+    replay_mutex_lock();
+    if (replay_next_event_is(EVENT_CHAR_WRITE)) {
+        *res = replay_get_dword();
+        *offset = replay_get_dword();
+        replay_finish_event();
+        replay_mutex_unlock();
+    } else {
+        replay_mutex_unlock();
+        error_report("Missing character write event in the replay log");
+        exit(1);
+    }
+}
+
+int replay_char_read_all_load(uint8_t *buf)
+{
+    replay_mutex_lock();
+    if (replay_next_event_is(EVENT_CHAR_READ_ALL)) {
+        size_t size;
+        int res;
+        replay_get_array(buf, &size);
+        replay_finish_event();
+        replay_mutex_unlock();
+        res = (int)size;
+        assert(res >= 0);
+        return res;
+    } else if (replay_next_event_is(EVENT_CHAR_READ_ALL_ERROR)) {
+        int res = replay_get_dword();
+        replay_finish_event();
+        replay_mutex_unlock();
+        return res;
+    } else {
+        replay_mutex_unlock();
+        error_report("Missing character read all event in the replay log");
+        exit(1);
+    }
+}
+
+void replay_char_read_all_save_error(int res)
+{
+    assert(res < 0);
+    replay_save_instructions();
+    replay_mutex_lock();
+    replay_put_event(EVENT_CHAR_READ_ALL_ERROR);
+    replay_put_dword(res);
+    replay_mutex_unlock();
+}
+
+void replay_char_read_all_save_buf(uint8_t *buf, int offset)
+{
+    replay_save_instructions();
+    replay_mutex_lock();
+    replay_put_event(EVENT_CHAR_READ_ALL);
+    replay_put_array(buf, offset);
+    replay_mutex_unlock();
+}
diff --git a/replay/replay-events.c b/replay/replay-events.c
index 2628109..ca940f7 100644
--- a/replay/replay-events.c
+++ b/replay/replay-events.c
@@ -48,6 +48,9 @@ static void replay_run_event(Event *event)
     case REPLAY_ASYNC_EVENT_INPUT_SYNC:
         qemu_input_event_sync_impl();
         break;
+    case REPLAY_ASYNC_EVENT_CHAR_READ:
+        replay_event_char_read_run(event->opaque);
+        break;
     default:
         error_report("Replay: invalid async event ID (%d) in the queue",
                     event->event_kind);
@@ -102,9 +105,9 @@ void replay_clear_events(void)
 }
 
 /*! Adds specified async event to the queue */
-static void replay_add_event(ReplayAsyncEventKind event_kind,
-                             void *opaque,
-                             void *opaque2, uint64_t id)
+void replay_add_event(ReplayAsyncEventKind event_kind,
+                      void *opaque,
+                      void *opaque2, uint64_t id)
 {
     assert(event_kind < REPLAY_ASYNC_COUNT);
 
@@ -168,6 +171,9 @@ static void replay_save_event(Event *event, int checkpoint)
             break;
         case REPLAY_ASYNC_EVENT_INPUT_SYNC:
             break;
+        case REPLAY_ASYNC_EVENT_CHAR_READ:
+            replay_event_char_read_save(event->opaque);
+            break;
         default:
             error_report("Unknown ID %d of replay event", read_event_kind);
             exit(1);
@@ -221,6 +227,11 @@ static Event *replay_read_event(int checkpoint)
         event->event_kind = read_event_kind;
         event->opaque = 0;
         return event;
+    case REPLAY_ASYNC_EVENT_CHAR_READ:
+        event = g_malloc0(sizeof(Event));
+        event->event_kind = read_event_kind;
+        event->opaque = replay_event_char_read_load();
+        return event;
     default:
         error_report("Unknown ID %d of replay event", read_event_kind);
         exit(1);
diff --git a/replay/replay-internal.h b/replay/replay-internal.h
index 5438ebd..11f9a85 100644
--- a/replay/replay-internal.h
+++ b/replay/replay-internal.h
@@ -24,6 +24,11 @@ enum ReplayEvents {
     EVENT_ASYNC,
     /* for shutdown request */
     EVENT_SHUTDOWN,
+    /* for character device write event */
+    EVENT_CHAR_WRITE,
+    /* for character device read all event */
+    EVENT_CHAR_READ_ALL,
+    EVENT_CHAR_READ_ALL_ERROR,
     /* for clock read/writes */
     /* some of greater codes are reserved for clocks */
     EVENT_CLOCK,
@@ -43,6 +48,7 @@ enum ReplayAsyncEventKind {
     REPLAY_ASYNC_EVENT_BH,
     REPLAY_ASYNC_EVENT_INPUT,
     REPLAY_ASYNC_EVENT_INPUT_SYNC,
+    REPLAY_ASYNC_EVENT_CHAR_READ,
     REPLAY_ASYNC_COUNT
 };
 
@@ -124,6 +130,9 @@ bool replay_has_events(void);
 void replay_save_events(int checkpoint);
 /*! Read events from the file into the input queue */
 void replay_read_events(int checkpoint);
+/*! Adds specified async event to the queue */
+void replay_add_event(ReplayAsyncEventKind event_kind, void *opaque,
+                      void *opaque2, uint64_t id);
 
 /* Input events */
 
@@ -136,4 +145,13 @@ void replay_add_input_event(struct InputEvent *event);
 /*! Adds input sync event to the queue */
 void replay_add_input_sync_event(void);
 
+/* Character devices */
+
+/*! Called to run char device read event. */
+void replay_event_char_read_run(void *opaque);
+/*! Writes char read event to the file. */
+void replay_event_char_read_save(void *opaque);
+/*! Reads char event read from the file. */
+void *replay_event_char_read_load(void);
+
 #endif
diff --git a/replay/replay.c b/replay/replay.c
index f8739c2..fcfde4f 100644
--- a/replay/replay.c
+++ b/replay/replay.c
@@ -20,7 +20,7 @@
 
 /* Current version of the replay mechanism.
    Increase it when file format changes. */
-#define REPLAY_VERSION              0xe02002
+#define REPLAY_VERSION              0xe02003
 /* Size of replay log header */
 #define HEADER_SIZE                 (sizeof(uint32_t) + sizeof(uint64_t))