diff --git a/Makefile.objs b/Makefile.objs
index c3e52c5..de38579 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -100,6 +100,7 @@ common-obj-y += msmouse.o ps2.o
 common-obj-y += qdev.o qdev-properties.o
 common-obj-y += block-migration.o
 common-obj-y += pflib.o
+common-obj-y += ft_trans_file.o
 
 common-obj-$(CONFIG_BRLAPI) += baum.o
 common-obj-$(CONFIG_POSIX) += migration-exec.o migration-unix.o migration-fd.o
diff --git a/ft_trans_file.c b/ft_trans_file.c
new file mode 100644
index 0000000..2672d40
--- /dev/null
+++ b/ft_trans_file.c
@@ -0,0 +1,626 @@
+/*
+ * Fault tolerant VM transaction QEMUFile
+ *
+ * Copyright (c) 2010 Nippon Telegraph and Telephone Corporation. 
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ * This source code is based on buffered_file.c.
+ * Copyright IBM, Corp. 2008
+ * Authors:
+ *  Anthony Liguori        <aliguori@us.ibm.com>
+ */
+
+#include "qemu-common.h"
+#include "qemu-error.h"
+#include "hw/hw.h"
+#include "qemu-timer.h"
+#include "sysemu.h"
+#include "qemu-char.h"
+#include "trace.h"
+#include "ft_trans_file.h"
+
+// #define DEBUG_FT_TRANSACTION
+
+typedef struct FtTransHdr
+{
+    uint16_t cmd;
+    uint16_t id;
+    uint32_t seq;
+    uint32_t payload_len;
+} FtTransHdr;
+
+typedef struct QEMUFileFtTrans
+{
+    FtTransPutBufferFunc *put_buffer;
+    FtTransGetBufferFunc *get_buffer;
+    FtTransPutReadyFunc *put_ready;
+    FtTransGetReadyFunc *get_ready;
+    FtTransWaitForUnfreezeFunc *wait_for_unfreeze;
+    FtTransCloseFunc *close;
+    void *opaque;
+    QEMUFile *file;
+
+    enum QEMU_VM_TRANSACTION_STATE state;
+    uint32_t seq;
+    uint16_t id;
+
+    int has_error;
+
+    bool freeze_output;
+    bool freeze_input;
+    bool rate_limit;
+    bool is_sender;
+    bool is_payload;
+
+    uint8_t *buf;
+    size_t buf_max_size;
+    size_t put_offset;
+    size_t get_offset;
+
+    FtTransHdr header;
+    size_t header_offset;
+} QEMUFileFtTrans;
+
+#define IO_BUF_SIZE 32768
+
+static void ft_trans_append(QEMUFileFtTrans *s,
+                            const uint8_t *buf, size_t size)
+{
+    if (size > (s->buf_max_size - s->put_offset)) {
+        trace_ft_trans_realloc(s->buf_max_size, size + 1024);
+        s->buf_max_size += size + 1024;
+        s->buf = qemu_realloc(s->buf, s->buf_max_size);
+    }
+
+    trace_ft_trans_append(size);
+    memcpy(s->buf + s->put_offset, buf, size);
+    s->put_offset += size;
+}
+
+static void ft_trans_flush(QEMUFileFtTrans *s)
+{
+    size_t offset = 0;
+
+    if (s->has_error) {
+        error_report("flush when error %d, bailing\n", s->has_error);
+        return;
+    }
+
+    while (offset < s->put_offset) {
+        ssize_t ret;
+
+        ret = s->put_buffer(s->opaque, s->buf + offset, s->put_offset - offset);
+        if (ret == -EAGAIN) {
+            break;
+        }
+
+        if (ret <= 0) {
+            error_report("error flushing data, %s\n", strerror(errno));
+            s->has_error = FT_TRANS_ERR_FLUSH;
+            break;
+        } else {
+            offset += ret;
+        }
+    }
+
+    trace_ft_trans_flush(offset, s->put_offset);
+    memmove(s->buf, s->buf + offset, s->put_offset - offset);
+    s->put_offset -= offset;
+    s->freeze_output = !!s->put_offset;
+}
+
+static ssize_t ft_trans_put(void *opaque, void *buf, int size)
+{
+    QEMUFileFtTrans *s = opaque;
+    size_t offset = 0;
+    ssize_t len;
+
+    /* flush buffered data before putting next */
+    if (s->put_offset) {
+        ft_trans_flush(s);
+    }
+
+    while (!s->freeze_output && offset < size) {
+        len = s->put_buffer(s->opaque, (uint8_t *)buf + offset, size - offset);
+
+        if (len == -EAGAIN) {
+            trace_ft_trans_freeze_output();
+            s->freeze_output = 1;
+            break;
+        }
+
+        if (len <= 0) {
+            error_report("putting data failed, %s\n", strerror(errno));
+            s->has_error = 1;
+            offset = -EINVAL;
+            break;
+        }
+
+        offset += len;
+    }
+
+    if (s->freeze_output) {
+        ft_trans_append(s, buf + offset, size - offset);
+        offset = size;
+    }
+
+    return offset;
+}
+
+static int ft_trans_send_header(QEMUFileFtTrans *s,
+                                enum QEMU_VM_TRANSACTION_STATE state,
+                                uint32_t payload_len)
+{
+    int ret;
+    FtTransHdr *hdr = &s->header;
+
+    trace_ft_trans_send_header(state);
+
+    hdr->cmd = s->state = state;
+    hdr->id = s->id;
+    hdr->seq = s->seq;
+    hdr->payload_len = payload_len;
+
+    ret = ft_trans_put(s, hdr, sizeof(*hdr));
+    if (ret < 0) {
+        error_report("send header failed\n");
+        s->has_error = FT_TRANS_ERR_SEND_HDR;
+    }
+
+    return ret;
+}
+
+static int ft_trans_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, int size)
+{
+    QEMUFileFtTrans *s = opaque;
+    ssize_t ret;
+
+    trace_ft_trans_put_buffer(size, pos);
+
+    if (s->has_error) {
+        error_report("put_buffer when error %d, bailing\n", s->has_error);
+        return -EINVAL;
+    }
+
+    /* assuming qemu_file_put_notify() is calling */
+    if (pos == 0 && size == 0) {
+        trace_ft_trans_put_ready();
+        ft_trans_flush(s);
+
+        if (!s->freeze_output) {
+            trace_ft_trans_cb(s->put_ready);
+            ret = s->put_ready();
+        }
+
+        ret = 0;
+        goto out;
+    }
+
+    ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_CONTINUE, size);
+    if (ret < 0) {
+        goto out;
+    }
+
+    ret = ft_trans_put(s, (uint8_t *)buf, size);
+    if (ret < 0) {
+        error_report("send palyload failed\n");
+        s->has_error = FT_TRANS_ERR_SEND_PAYLOAD;
+        goto out;
+    }
+
+    s->seq++;
+
+out:
+    return ret;
+}
+
+static int ft_trans_fill_buffer(void *opaque, void *buf, int size)
+{
+    QEMUFileFtTrans *s = opaque;
+    size_t offset = 0;
+    ssize_t len;
+
+    s->freeze_input = 0;
+
+    while (offset < size) {
+        len = s->get_buffer(s->opaque, (uint8_t *)buf + offset,
+                            0, size - offset);
+        if (len == -EAGAIN) {
+            trace_ft_trans_freeze_input();
+            s->freeze_input = 1;
+            break;
+        }
+
+        if (len <= 0) {
+            error_report("fill buffer failed, %s\n", strerror(errno));
+            s->has_error = 1;
+            return -EINVAL;
+        }
+
+        offset += len;
+    }
+
+    return offset;
+}
+
+static int ft_trans_recv_header(QEMUFileFtTrans *s)
+{
+    int ret;
+    char *buf = (char *)&s->header + s->header_offset;
+
+    ret = ft_trans_fill_buffer(s, buf, sizeof(FtTransHdr) - s->header_offset);
+    if (ret < 0) {
+        error_report("recv header failed\n");
+        s->has_error = FT_TRANS_ERR_RECV_HDR;
+        goto out;
+    }
+
+    s->header_offset += ret;
+    if (s->header_offset == sizeof(FtTransHdr)) {
+        trace_ft_trans_recv_header(s->header.cmd);
+        s->state = s->header.cmd;
+        s->header_offset = 0;
+
+        if (!s->is_sender) {
+            s->id = s->header.id;
+            s->seq = s->header.seq;
+        }
+    }
+
+out:
+    return ret;
+}
+
+static int ft_trans_recv_payload(QEMUFileFtTrans *s)
+{
+    QEMUFile *f = s->file;    
+    int ret = -1;
+
+    /* extend QEMUFile buf if there weren't enough space */
+    if (s->header.payload_len > (s->buf_max_size - s->get_offset)) {
+        s->buf_max_size += (s->header.payload_len -
+                            (s->buf_max_size - s->get_offset));
+        s->buf = qemu_realloc_buffer(f, s->buf_max_size);
+    }
+
+    ret = ft_trans_fill_buffer(s, s->buf + s->get_offset,
+                               s->header.payload_len);
+    if (ret < 0) {
+        error_report("recv payload failed\n");
+        s->has_error = FT_TRANS_ERR_RECV_PAYLOAD;
+        goto out;
+    }
+
+    trace_ft_trans_recv_payload(ret, s->header.payload_len, s->get_offset);
+
+    s->header.payload_len -= ret;
+    s->get_offset += ret;
+    s->is_payload = !!s->header.payload_len;
+
+out:
+    return ret;
+}
+
+static int ft_trans_recv(QEMUFileFtTrans *s)
+{
+    int ret;
+
+    /* get payload and return */
+    if (s->is_payload) {
+        ret = ft_trans_recv_payload(s);
+        goto out;
+    }
+
+    ret = ft_trans_recv_header(s);
+    if (ret < 0 || s->freeze_input) {
+        goto out;
+    }
+
+    switch (s->state) {
+    case QEMU_VM_TRANSACTION_BEGIN:
+        /* CONTINUE or COMMIT should come shortly */
+        s->is_payload = 0;
+        break;
+
+    case QEMU_VM_TRANSACTION_CONTINUE:
+        /* get payload */
+        s->is_payload = 1;
+        break;
+
+    case QEMU_VM_TRANSACTION_COMMIT:
+        ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_ACK, 0);
+        if (ret < 0) {
+            goto out;
+        }
+
+        trace_ft_trans_cb(s->get_ready);
+        if ((ret = s->get_ready(s->opaque)) < 0) {
+            goto out;
+        }
+
+        qemu_clear_buffer(s->file);
+        s->get_offset = 0;
+        s->is_payload = 0;
+
+        break;
+
+    case QEMU_VM_TRANSACTION_ATOMIC:
+        /* not implemented yet */
+        error_report("QEMU_VM_TRANSACTION_ATOMIC not implemented. %d\n",
+                ret);
+        break;
+
+    case QEMU_VM_TRANSACTION_CANCEL:
+        /* return -EINVAL until migrate cancel on recevier side is supported */
+        ret = -EINVAL;
+        break;
+
+    default:
+        error_report("unknown QEMU_VM_TRANSACTION_STATE %d\n", ret);
+        s->has_error = FT_TRANS_ERR_STATE_INVALID;
+        ret = -EINVAL;
+    }
+
+out:
+    return ret;
+}
+
+static int ft_trans_get_buffer(void *opaque, uint8_t *buf,
+                               int64_t pos, int size)
+{
+    QEMUFileFtTrans *s = opaque;
+    int ret;
+
+    if (s->has_error) {
+        error_report("get_buffer when error %d, bailing\n", s->has_error);
+        return -EINVAL;
+    }
+
+    /* assuming qemu_file_get_notify() is calling */
+    if (pos == 0 && size == 0) {
+        trace_ft_trans_get_ready();
+        s->freeze_input = 0;
+
+        /* sender should be waiting for ACK */
+        if (s->is_sender) {
+            ret = ft_trans_recv_header(s);
+            if (s->freeze_input) {
+                ret = 0;
+                goto out;
+            }
+            if (ret < 0) {
+                error_report("recv ack failed\n");
+                goto out;
+            }
+
+            if (s->state != QEMU_VM_TRANSACTION_ACK) {
+                error_report("recv invalid state %d\n", s->state);
+                s->has_error = FT_TRANS_ERR_STATE_INVALID;
+                ret = -EINVAL;
+                goto out;
+            }
+
+            trace_ft_trans_cb(s->get_ready);
+            ret = s->get_ready(s->opaque);
+            if (ret < 0) {
+                goto out;
+            }
+
+            /* proceed trans id */
+            s->id++;
+
+            return 0;
+        }
+
+        /* set QEMUFile buf at beginning */
+        if (!s->buf) {
+            s->buf = buf;
+        }
+
+        ret = ft_trans_recv(s);
+        goto out;
+    }
+
+    ret = s->get_offset;
+
+out:
+    return ret;
+}
+
+static int ft_trans_close(void *opaque)
+{
+    QEMUFileFtTrans *s = opaque;
+    int ret;
+
+    trace_ft_trans_close();
+    ret = s->close(s->opaque);
+    if (s->is_sender) {
+        qemu_free(s->buf);
+    }
+    qemu_free(s);
+
+    return ret;
+}
+
+static int ft_trans_rate_limit(void *opaque)
+{
+    QEMUFileFtTrans *s = opaque;
+
+    if (s->has_error) {
+        return 0;
+    }
+
+    if (s->rate_limit && s->freeze_output) {
+        return 1;
+    }
+
+    return 0;
+}
+
+static int64_t ft_trans_set_rate_limit(void *opaque, int64_t new_rate)
+{
+    QEMUFileFtTrans *s = opaque;
+
+    if (s->has_error) {
+        goto out;
+    }
+
+    s->rate_limit = !!new_rate;
+    
+out:
+    return s->rate_limit;
+}
+
+int ft_trans_begin(void *opaque)
+{
+    QEMUFileFtTrans *s = opaque;
+    int ret;
+    s->seq = 0;
+
+    /* receiver sends QEMU_VM_TRANSACTION_ACK to start transaction */
+    if (!s->is_sender) {
+        if (s->state != QEMU_VM_TRANSACTION_INIT) {
+            error_report("invalid state %d\n", s->state);
+            s->has_error = FT_TRANS_ERR_STATE_INVALID;
+            ret = -EINVAL;
+        }
+
+        ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_ACK, 0);
+        goto out;
+    } 
+
+    /* sender waits for QEMU_VM_TRANSACTION_ACK to start transaction */
+    if (s->state == QEMU_VM_TRANSACTION_INIT) {
+    retry:
+        ret = ft_trans_recv_header(s);
+        if (s->freeze_input) {
+            goto retry;
+        }
+        if (ret < 0) {
+            error_report("recv ack failed\n");
+            goto out;
+        }
+
+        if (s->state != QEMU_VM_TRANSACTION_ACK) {
+            error_report("recv invalid state %d\n", s->state);
+            s->has_error = FT_TRANS_ERR_STATE_INVALID;
+            ret = -EINVAL;
+            goto out;
+        }
+    }
+
+    ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_BEGIN, 0);
+    if (ret < 0) {
+        goto out;
+    }
+
+    s->state = QEMU_VM_TRANSACTION_CONTINUE;
+
+out:
+    return ret;
+}
+
+int ft_trans_commit(void *opaque)
+{
+    QEMUFileFtTrans *s = opaque;
+    int ret;
+
+    if (!s->is_sender) {
+        ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_ACK, 0);
+        goto out;
+    }
+
+    /* sender should flush buf before sending COMMIT */
+    qemu_fflush(s->file);
+
+    ret = ft_trans_send_header(s, QEMU_VM_TRANSACTION_COMMIT, 0);
+    if (ret < 0) {
+        goto out;
+    }
+
+    while (!s->has_error && s->put_offset) {
+        ft_trans_flush(s);
+        if (s->freeze_output) {
+            s->wait_for_unfreeze(s);
+        }
+    }
+
+    if (s->has_error) {
+        ret = -EINVAL;
+        goto out;
+    }
+
+    ret = ft_trans_recv_header(s);
+    if (s->freeze_input) {
+        ret = -EAGAIN;
+        goto out;
+    }
+    if (ret < 0) {
+        error_report("recv ack failed\n");
+        goto out;
+    }
+
+    if (s->state != QEMU_VM_TRANSACTION_ACK) {
+        error_report("recv invalid state %d\n", s->state);
+        s->has_error = FT_TRANS_ERR_STATE_INVALID;
+        ret = -EINVAL;
+        goto out;
+    }
+    
+    s->id++;
+    ret = 0;
+
+out:
+    return ret;
+}
+
+int ft_trans_cancel(void *opaque)
+{
+    QEMUFileFtTrans *s = opaque;
+
+    /* invalid until migrate cancel on recevier side is supported */
+    if (!s->is_sender) {
+        return -EINVAL;
+    } 
+    
+    return ft_trans_send_header(s, QEMU_VM_TRANSACTION_CANCEL, 0);
+}
+
+QEMUFile *qemu_fopen_ops_ft_trans(void *opaque,
+                                  FtTransPutBufferFunc *put_buffer,
+                                  FtTransGetBufferFunc *get_buffer,
+                                  FtTransPutReadyFunc *put_ready,
+                                  FtTransGetReadyFunc *get_ready,
+                                  FtTransWaitForUnfreezeFunc *wait_for_unfreeze,
+                                  FtTransCloseFunc *close,
+                                  bool is_sender)
+{
+    QEMUFileFtTrans *s;
+
+    s = qemu_mallocz(sizeof(*s));
+
+    s->opaque = opaque;
+    s->put_buffer = put_buffer;
+    s->get_buffer = get_buffer;
+    s->put_ready = put_ready;
+    s->get_ready = get_ready;
+    s->wait_for_unfreeze = wait_for_unfreeze;
+    s->close = close;
+    s->is_sender = is_sender;
+    s->id = 0;
+    s->seq = 0;
+    s->rate_limit = 1;
+
+    if (!s->is_sender) {
+        s->buf_max_size = IO_BUF_SIZE;
+    }
+
+ 
+    s->file = qemu_fopen_ops(s, ft_trans_put_buffer, ft_trans_get_buffer,
+                             ft_trans_close, ft_trans_rate_limit, 
+                             ft_trans_set_rate_limit, NULL);
+
+    return s->file;
+}
diff --git a/ft_trans_file.h b/ft_trans_file.h
new file mode 100644
index 0000000..d7e221b
--- /dev/null
+++ b/ft_trans_file.h
@@ -0,0 +1,72 @@
+/*
+ * Fault tolerant VM transaction QEMUFile
+ *
+ * Copyright (c) 2010 Nippon Telegraph and Telephone Corporation. 
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ * This source code is based on buffered_file.h.
+ * Copyright IBM, Corp. 2008
+ * Authors:
+ *  Anthony Liguori        <aliguori@us.ibm.com>
+ */
+
+#ifndef QEMU_FT_TRANSACTION_FILE_H
+#define QEMU_FT_TRANSACTION_FILE_H
+
+#include "hw/hw.h"
+
+enum QEMU_VM_TRANSACTION_STATE {
+    QEMU_VM_TRANSACTION_NACK = -1,
+    QEMU_VM_TRANSACTION_INIT,
+    QEMU_VM_TRANSACTION_BEGIN,
+    QEMU_VM_TRANSACTION_CONTINUE,
+    QEMU_VM_TRANSACTION_COMMIT,
+    QEMU_VM_TRANSACTION_CANCEL,
+    QEMU_VM_TRANSACTION_ATOMIC,
+    QEMU_VM_TRANSACTION_ACK,
+};
+
+enum FT_MODE {
+    FT_ERROR = -1,
+    FT_OFF,
+    FT_INIT,
+    FT_TRANSACTION_BEGIN,
+    FT_TRANSACTION_ITER,
+    FT_TRANSACTION_COMMIT,
+    FT_TRANSACTION_ATOMIC,
+    FT_TRANSACTION_RECV,
+};
+extern enum FT_MODE ft_mode;
+
+#define FT_TRANS_ERR_UNKNOWN       0x01 /* Unknown error */
+#define FT_TRANS_ERR_SEND_HDR      0x02 /* Send header failed */
+#define FT_TRANS_ERR_RECV_HDR      0x03 /* Recv header failed */
+#define FT_TRANS_ERR_SEND_PAYLOAD  0x04 /* Send payload failed */
+#define FT_TRANS_ERR_RECV_PAYLOAD  0x05 /* Recv payload failed */
+#define FT_TRANS_ERR_FLUSH         0x06 /* Flush buffered data failed */
+#define FT_TRANS_ERR_STATE_INVALID 0x07 /* Invalid state */
+
+typedef ssize_t (FtTransPutBufferFunc)(void *opaque, const void *data, size_t size);
+typedef int (FtTransGetBufferFunc)(void *opaque, uint8_t *buf, int64_t pos, size_t size);
+typedef ssize_t (FtTransPutVectorFunc)(void *opaque, const struct iovec *iov, int iovcnt);
+typedef int (FtTransPutReadyFunc)(void);
+typedef int (FtTransGetReadyFunc)(void *opaque);
+typedef void (FtTransWaitForUnfreezeFunc)(void *opaque);
+typedef int (FtTransCloseFunc)(void *opaque);
+
+int ft_trans_begin(void *opaque);
+int ft_trans_commit(void *opaque);
+int ft_trans_cancel(void *opaque);
+
+QEMUFile *qemu_fopen_ops_ft_trans(void *opaque, 
+                                  FtTransPutBufferFunc *put_buffer,
+                                  FtTransGetBufferFunc *get_buffer,
+                                  FtTransPutReadyFunc *put_ready,
+                                  FtTransGetReadyFunc *get_ready,
+                                  FtTransWaitForUnfreezeFunc *wait_for_unfreeze,
+                                  FtTransCloseFunc *close,
+                                  bool is_sender);
+
+#endif
diff --git a/migration.c b/migration.c
index a400199..01b723d 100644
--- a/migration.c
+++ b/migration.c
@@ -15,6 +15,7 @@
 #include "migration.h"
 #include "monitor.h"
 #include "buffered_file.h"
+#include "ft_trans_file.h"
 #include "sysemu.h"
 #include "block.h"
 #include "qemu_socket.h"
@@ -31,6 +32,8 @@
     do { } while (0)
 #endif
 
+enum FT_MODE ft_mode = FT_OFF;
+
 /* Migration speed throttling */
 static int64_t max_throttle = (32 << 20);
 
diff --git a/trace-events b/trace-events
index e8fed0f..b8c6012 100644
--- a/trace-events
+++ b/trace-events
@@ -213,3 +213,19 @@ disable qed_aio_write_data(void *s, void *acb, int ret, uint64_t offset, size_t
 disable qed_aio_write_prefill(void *s, void *acb, uint64_t start, size_t len, uint64_t offset) "s %p acb %p start %"PRIu64" len %zu offset %"PRIu64""
 disable qed_aio_write_postfill(void *s, void *acb, uint64_t start, size_t len, uint64_t offset) "s %p acb %p start %"PRIu64" len %zu offset %"PRIu64""
 disable qed_aio_write_main(void *s, void *acb, int ret, uint64_t offset, size_t len) "s %p acb %p ret %d offset %"PRIu64" len %zu"
+
+# ft_trans_file.c
+disable ft_trans_realloc(size_t old_size, size_t new_size) "increasing buffer from %zu by %zu"
+disable ft_trans_append(size_t size) "buffering %zu bytes"
+disable ft_trans_flush(size_t size, size_t req) "flushed %zu of %zu bytes"
+disable ft_trans_send_header(uint16_t cmd) "send header %d"
+disable ft_trans_recv_header(uint16_t cmd) "recv header %d"
+disable ft_trans_put_buffer(size_t size, int64_t pos) "putting %d bytes at %"PRId64""
+disable ft_trans_recv_payload(size_t len, uint32_t hdr, size_t total) "recv %d of %d total %d"
+disable ft_trans_close(void) "closing"
+disable ft_trans_freeze_output(void) "backend not ready, freezing output"
+disable ft_trans_freeze_input(void) "backend not ready, freezing input"
+disable ft_trans_put_ready(void) "file is ready to put"
+disable ft_trans_get_ready(void) "file is ready to get"
+disable ft_trans_cb(void *cb) "callback %p"
+
