diff --git a/iolog.c b/iolog.c
new file mode 100644
index 0000000..f962864
--- /dev/null
+++ b/iolog.c
@@ -0,0 +1,541 @@
+/*
+ * Code related to writing an iolog of what a thread is doing, and to
+ * later read that back and replay
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <libgen.h>
+#include <assert.h>
+#include "flist.h"
+#include "fio.h"
+#include "verify.h"
+#include "trim.h"
+
+static const char iolog_ver2[] = "fio version 2 iolog";
+
+void queue_io_piece(struct thread_data *td, struct io_piece *ipo)
+{
+	flist_add_tail(&ipo->list, &td->io_log_list);
+	td->total_io_size += ipo->len;
+}
+
+void log_io_u(struct thread_data *td, struct io_u *io_u)
+{
+	const char *act[] = { "read", "write", "sync", "datasync",
+				"sync_file_range", "wait", "trim" };
+
+	assert(io_u->ddir <= 6);
+
+	if (!td->o.write_iolog_file)
+		return;
+
+	fprintf(td->iolog_f, "%s %s %llu %lu\n", io_u->file->file_name,
+						act[io_u->ddir], io_u->offset,
+						io_u->buflen);
+}
+
+void log_file(struct thread_data *td, struct fio_file *f,
+	      enum file_log_act what)
+{
+	const char *act[] = { "add", "open", "close" };
+
+	assert(what < 3);
+
+	if (!td->o.write_iolog_file)
+		return;
+
+
+	/*
+	 * this happens on the pre-open/close done before the job starts
+	 */
+	if (!td->iolog_f)
+		return;
+
+	fprintf(td->iolog_f, "%s %s\n", f->file_name, act[what]);
+}
+
+static void iolog_delay(struct thread_data *td, unsigned long delay)
+{
+	unsigned long usec = utime_since_now(&td->last_issue);
+
+	if (delay < usec)
+		return;
+
+	delay -= usec;
+
+	/*
+	 * less than 100 usec delay, just regard it as noise
+	 */
+	if (delay < 100)
+		return;
+
+	usec_sleep(td, delay);
+}
+
+static int ipo_special(struct thread_data *td, struct io_piece *ipo)
+{
+	struct fio_file *f;
+	int ret;
+
+	/*
+	 * Not a special ipo
+	 */
+	if (ipo->ddir != DDIR_INVAL)
+		return 0;
+
+	f = td->files[ipo->fileno];
+
+	switch (ipo->file_action) {
+	case FIO_LOG_OPEN_FILE:
+		ret = td_io_open_file(td, f);
+		if (!ret)
+			break;
+		td_verror(td, ret, "iolog open file");
+		return -1;
+	case FIO_LOG_CLOSE_FILE:
+		td_io_close_file(td, f);
+		break;
+	case FIO_LOG_UNLINK_FILE:
+		unlink(f->file_name);
+		break;
+	default:
+		log_err("fio: bad file action %d\n", ipo->file_action);
+		break;
+	}
+
+	return 1;
+}
+
+int read_iolog_get(struct thread_data *td, struct io_u *io_u)
+{
+	struct io_piece *ipo;
+	unsigned long elapsed;
+	
+	while (!flist_empty(&td->io_log_list)) {
+		int ret;
+
+		ipo = flist_entry(td->io_log_list.next, struct io_piece, list);
+		flist_del(&ipo->list);
+		remove_trim_entry(td, ipo);
+
+		ret = ipo_special(td, ipo);
+		if (ret < 0) {
+			free(ipo);
+			break;
+		} else if (ret > 0) {
+			free(ipo);
+			continue;
+		}
+
+		io_u->ddir = ipo->ddir;
+		if (ipo->ddir != DDIR_WAIT) {
+			io_u->offset = ipo->offset;
+			io_u->buflen = ipo->len;
+			io_u->file = td->files[ipo->fileno];
+			get_file(io_u->file);
+			dprint(FD_IO, "iolog: get %llu/%lu/%s\n", io_u->offset,
+						io_u->buflen, io_u->file->file_name);
+			if (ipo->delay)
+				iolog_delay(td, ipo->delay);
+		} else {
+			elapsed = mtime_since_genesis();
+			if (ipo->delay > elapsed)
+				usec_sleep(td, (ipo->delay - elapsed) * 1000);
+				
+		}
+
+		free(ipo);
+		
+		if (io_u->ddir != DDIR_WAIT)
+			return 0;
+	}
+
+	td->done = 1;
+	return 1;
+}
+
+void prune_io_piece_log(struct thread_data *td)
+{
+	struct io_piece *ipo;
+	struct rb_node *n;
+
+	while ((n = rb_first(&td->io_hist_tree)) != NULL) {
+		ipo = rb_entry(n, struct io_piece, rb_node);
+		rb_erase(n, &td->io_hist_tree);
+		remove_trim_entry(td, ipo);
+		td->io_hist_len--;
+		free(ipo);
+	}
+
+	while (!flist_empty(&td->io_hist_list)) {
+		ipo = flist_entry(td->io_hist_list.next, struct io_piece, list);
+		flist_del(&ipo->list);
+		remove_trim_entry(td, ipo);
+		td->io_hist_len--;
+		free(ipo);
+	}
+}
+
+/*
+ * log a successful write, so we can unwind the log for verify
+ */
+void log_io_piece(struct thread_data *td, struct io_u *io_u)
+{
+	struct rb_node **p, *parent;
+	struct io_piece *ipo, *__ipo;
+
+	ipo = malloc(sizeof(struct io_piece));
+	init_ipo(ipo);
+	ipo->file = io_u->file;
+	ipo->offset = io_u->offset;
+	ipo->len = io_u->buflen;
+
+	if (io_u_should_trim(td, io_u)) {
+		flist_add_tail(&ipo->trim_list, &td->trim_list);
+		td->trim_entries++;
+	}
+
+	/*
+	 * We don't need to sort the entries, if:
+	 *
+	 *	Sequential writes, or
+	 *	Random writes that lay out the file as it goes along
+	 *
+	 * For both these cases, just reading back data in the order we
+	 * wrote it out is the fastest.
+	 *
+	 * One exception is if we don't have a random map AND we are doing
+	 * verifies, in that case we need to check for duplicate blocks and
+	 * drop the old one, which we rely on the rb insert/lookup for
+	 * handling.
+	 */
+	if ((!td_random(td) || !td->o.overwrite) &&
+	      (file_randommap(td, ipo->file) || td->o.verify == VERIFY_NONE)) {
+		INIT_FLIST_HEAD(&ipo->list);
+		flist_add_tail(&ipo->list, &td->io_hist_list);
+		ipo->flags |= IP_F_ONLIST;
+		td->io_hist_len++;
+		return;
+	}
+
+	RB_CLEAR_NODE(&ipo->rb_node);
+
+	/*
+	 * Sort the entry into the verification list
+	 */
+restart:
+	p = &td->io_hist_tree.rb_node;
+	parent = NULL;
+	while (*p) {
+		parent = *p;
+
+		__ipo = rb_entry(parent, struct io_piece, rb_node);
+		if (ipo->file < __ipo->file)
+			p = &(*p)->rb_left;
+		else if (ipo->file > __ipo->file)
+			p = &(*p)->rb_right;
+		else if (ipo->offset < __ipo->offset)
+			p = &(*p)->rb_left;
+		else if (ipo->offset > __ipo->offset)
+			p = &(*p)->rb_right;
+		else {
+			assert(ipo->len == __ipo->len);
+			td->io_hist_len--;
+			rb_erase(parent, &td->io_hist_tree);
+			remove_trim_entry(td, __ipo);
+			free(__ipo);
+			goto restart;
+		}
+	}
+
+	rb_link_node(&ipo->rb_node, parent, p);
+	rb_insert_color(&ipo->rb_node, &td->io_hist_tree);
+	ipo->flags |= IP_F_ONRB;
+	td->io_hist_len++;
+}
+
+void write_iolog_close(struct thread_data *td)
+{
+	fflush(td->iolog_f);
+	fclose(td->iolog_f);
+	free(td->iolog_buf);
+	td->iolog_f = NULL;
+	td->iolog_buf = NULL;
+}
+
+/*
+ * Read version 2 iolog data. It is enhanced to include per-file logging,
+ * syncs, etc.
+ */
+static int read_iolog2(struct thread_data *td, FILE *f)
+{
+	unsigned long long offset;
+	unsigned int bytes;
+	int reads, writes, waits, fileno = 0, file_action = 0; /* stupid gcc */
+	char *fname, *act;
+	char *str, *p;
+	enum fio_ddir rw;
+
+	free_release_files(td);
+
+	/*
+	 * Read in the read iolog and store it, reuse the infrastructure
+	 * for doing verifications.
+	 */
+	str = malloc(4096);
+	fname = malloc(256+16);
+	act = malloc(256+16);
+
+	reads = writes = waits = 0;
+	while ((p = fgets(str, 4096, f)) != NULL) {
+		struct io_piece *ipo;
+		int r;
+
+		r = sscanf(p, "%256s %256s %llu %u", fname, act, &offset,
+									&bytes);
+		if (r == 4) {
+			/*
+			 * Check action first
+			 */
+			if (!strcmp(act, "wait"))
+				rw = DDIR_WAIT;
+			else if (!strcmp(act, "read"))
+				rw = DDIR_READ;
+			else if (!strcmp(act, "write"))
+				rw = DDIR_WRITE;
+			else if (!strcmp(act, "sync"))
+				rw = DDIR_SYNC;
+			else if (!strcmp(act, "datasync"))
+				rw = DDIR_DATASYNC;
+			else if (!strcmp(act, "trim"))
+				rw = DDIR_TRIM;
+			else {
+				log_err("fio: bad iolog file action: %s\n",
+									act);
+				continue;
+			}
+		} else if (r == 2) {
+			rw = DDIR_INVAL;
+			if (!strcmp(act, "add")) {
+				td->o.nr_files++;
+				fileno = add_file(td, fname);
+				file_action = FIO_LOG_ADD_FILE;
+				continue;
+			} else if (!strcmp(act, "open")) {
+				fileno = get_fileno(td, fname);
+				file_action = FIO_LOG_OPEN_FILE;
+			} else if (!strcmp(act, "close")) {
+				fileno = get_fileno(td, fname);
+				file_action = FIO_LOG_CLOSE_FILE;
+			} else {
+				log_err("fio: bad iolog file action: %s\n",
+									act);
+				continue;
+			}
+		} else {
+			log_err("bad iolog2: %s", p);
+			continue;
+		}
+
+		if (rw == DDIR_READ)
+			reads++;
+		else if (rw == DDIR_WRITE) {
+			/*
+			 * Don't add a write for ro mode
+			 */
+			if (read_only)
+				continue;
+			writes++;
+		} else if (rw == DDIR_WAIT) {
+			waits++;
+		} else if (rw == DDIR_INVAL) {
+		} else if (!ddir_sync(rw)) {
+			log_err("bad ddir: %d\n", rw);
+			continue;
+		}
+
+		/*
+		 * Make note of file
+		 */
+		ipo = malloc(sizeof(*ipo));
+		init_ipo(ipo);
+		ipo->ddir = rw;
+		if (rw == DDIR_WAIT) {
+			ipo->delay = offset;
+		} else {
+			ipo->offset = offset;
+			ipo->len = bytes;
+			if (bytes > td->o.max_bs[rw])
+				td->o.max_bs[rw] = bytes;
+			ipo->fileno = fileno;
+			ipo->file_action = file_action;
+		}
+			
+		queue_io_piece(td, ipo);
+	}
+
+	free(str);
+	free(act);
+	free(fname);
+
+	if (writes && read_only) {
+		log_err("fio: <%s> skips replay of %d writes due to"
+			" read-only\n", td->o.name, writes);
+		writes = 0;
+	}
+
+	if (!reads && !writes && !waits)
+		return 1;
+	else if (reads && !writes)
+		td->o.td_ddir = TD_DDIR_READ;
+	else if (!reads && writes)
+		td->o.td_ddir = TD_DDIR_WRITE;
+	else
+		td->o.td_ddir = TD_DDIR_RW;
+
+	return 0;
+}
+
+/*
+ * open iolog, check version, and call appropriate parser
+ */
+static int init_iolog_read(struct thread_data *td)
+{
+	char buffer[256], *p;
+	FILE *f;
+	int ret;
+
+	f = fopen(td->o.read_iolog_file, "r");
+	if (!f) {
+		perror("fopen read iolog");
+		return 1;
+	}
+
+	p = fgets(buffer, sizeof(buffer), f);
+	if (!p) {
+		td_verror(td, errno, "iolog read");
+		log_err("fio: unable to read iolog\n");
+		fclose(f);
+		return 1;
+	}
+
+	/*
+	 * version 2 of the iolog stores a specific string as the
+	 * first line, check for that
+	 */
+	if (!strncmp(iolog_ver2, buffer, strlen(iolog_ver2)))
+		ret = read_iolog2(td, f);
+	else {
+		log_err("fio: iolog version 1 is no longer supported\n");
+		ret = 1;
+	}
+
+	fclose(f);
+	return ret;
+}
+
+/*
+ * Set up a log for storing io patterns.
+ */
+static int init_iolog_write(struct thread_data *td)
+{
+	struct fio_file *ff;
+	FILE *f;
+	unsigned int i;
+
+	f = fopen(td->o.write_iolog_file, "a");
+	if (!f) {
+		perror("fopen write iolog");
+		return 1;
+	}
+
+	/*
+	 * That's it for writing, setup a log buffer and we're done.
+	  */
+	td->iolog_f = f;
+	td->iolog_buf = malloc(8192);
+	setvbuf(f, td->iolog_buf, _IOFBF, 8192);
+
+	/*
+	 * write our version line
+	 */
+	if (fprintf(f, "%s\n", iolog_ver2) < 0) {
+		perror("iolog init\n");
+		return 1;
+	}
+
+	/*
+	 * add all known files
+	 */
+	for_each_file(td, ff, i)
+		log_file(td, ff, FIO_LOG_ADD_FILE);
+
+	return 0;
+}
+
+int init_iolog(struct thread_data *td)
+{
+	int ret = 0;
+
+	if (td->o.read_iolog_file) {
+		/*
+		 * Check if it's a blktrace file and load that if possible.
+		 * Otherwise assume it's a normal log file and load that.
+		 */
+		if (is_blktrace(td->o.read_iolog_file))
+			ret = load_blktrace(td, td->o.read_iolog_file);
+		else
+			ret = init_iolog_read(td);
+	} else if (td->o.write_iolog_file)
+		ret = init_iolog_write(td);
+
+	return ret;
+}
+
+void setup_log(struct io_log **log)
+{
+	struct io_log *l = malloc(sizeof(*l));
+
+	l->nr_samples = 0;
+	l->max_samples = 1024;
+	l->log = malloc(l->max_samples * sizeof(struct io_sample));
+	*log = l;
+}
+
+void __finish_log(struct io_log *log, const char *name)
+{
+	unsigned int i;
+	FILE *f;
+
+	f = fopen(name, "a");
+	if (!f) {
+		perror("fopen log");
+		return;
+	}
+
+	for (i = 0; i < log->nr_samples; i++) {
+		fprintf(f, "%lu, %lu, %u, %u\n", log->log[i].time,
+						log->log[i].val,
+						log->log[i].ddir,
+						log->log[i].bs);
+	}
+
+	fclose(f);
+	free(log->log);
+	free(log);
+}
+
+void finish_log_named(struct thread_data *td, struct io_log *log,
+		       const char *prefix, const char *postfix)
+{
+	char file_name[256], *p;
+
+	snprintf(file_name, 200, "%s_%s.log", prefix, postfix);
+	p = basename(file_name);
+	__finish_log(log, p);
+}
+
+void finish_log(struct thread_data *td, struct io_log *log, const char *name)
+{
+	finish_log_named(td, log, td->o.name, name);
+}