diff --git a/protocol.md b/protocol.md
index 6cedbbec..9cc333c6 100644
--- a/protocol.md
+++ b/protocol.md
@@ -353,7 +353,7 @@ At most count bytes will be returned in data. If count is not zero in the respon
 
 #### fsync - flush any cached data to disk
 ```
-size[4] Tfsync tag[2] fid[4]
+size[4] Tfsync tag[2] fid[4] datasync[4]
 size[4] Rfsync tag[2]
 ```
 fsync tells the server to flush any cached data associated with fid, previously opened with lopen.
diff --git a/src/daemon/ioctx.c b/src/daemon/ioctx.c
index c5ba1d4f..09529251 100644
--- a/src/daemon/ioctx.c
+++ b/src/daemon/ioctx.c
@@ -348,8 +348,10 @@ ioctx_readdir(IOCtx ioctx, long *offset)
 }
 
 int
-ioctx_fsync(IOCtx ioctx)
+ioctx_fsync(IOCtx ioctx, int datasync)
 {
+    if (datasync)
+        return fdatasync (ioctx->fd);
     return fsync (ioctx->fd);
 }
 
diff --git a/src/daemon/ioctx.h b/src/daemon/ioctx.h
index 0b8a24b6..74e08ccf 100644
--- a/src/daemon/ioctx.h
+++ b/src/daemon/ioctx.h
@@ -27,7 +27,7 @@ int     ioctx_pwrite (IOCtx ioctx, const void *buf, size_t count, off_t offset);
 struct dirent *ioctx_readdir(IOCtx ioctx, long *new_offset);
 void    ioctx_rewinddir (IOCtx ioctx);
 void    ioctx_seekdir (IOCtx ioctx, long offset);
-int     ioctx_fsync (IOCtx ioctx);
+int     ioctx_fsync (IOCtx ioctx, int datasync);
 int     ioctx_flock (IOCtx ioctx, int operation);
 int     ioctx_testlock (IOCtx ioctx, int operation);
 
diff --git a/src/daemon/ops.c b/src/daemon/ops.c
index 9b07f84c..f3de61d0 100644
--- a/src/daemon/ops.c
+++ b/src/daemon/ops.c
@@ -130,7 +130,7 @@ Npfcall     *diod_getattr(Npfid *fid, u64 request_mask);
 Npfcall     *diod_setattr (Npfid *fid, u32 valid, u32 mode, u32 uid, u32 gid, u64 size,
                         u64 atime_sec, u64 atime_nsec, u64 mtime_sec, u64 mtime_nsec);
 Npfcall     *diod_readdir(Npfid *fid, u64 offset, u32 count, Npreq *req);
-Npfcall     *diod_fsync (Npfid *fid);
+Npfcall     *diod_fsync (Npfid *fid, u32 datasync);
 Npfcall     *diod_lock (Npfid *fid, u8 type, u32 flags, u64 start, u64 length,
                         u32 proc_id, Npstr *client_id);
 Npfcall     *diod_getlock (Npfid *fid, u8 type, u64 start, u64 length,
@@ -1226,7 +1226,7 @@ diod_readdir(Npfid *fid, u64 offset, u32 count, Npreq *req)
 }
 
 Npfcall*
-diod_fsync (Npfid *fid)
+diod_fsync (Npfid *fid, u32 datasync)
 {
     Fid *f = fid->aux;
     Npfcall *ret;
@@ -1236,7 +1236,7 @@ diod_fsync (Npfid *fid)
         np_uerror (EBADF);
         goto error;
     }
-    if (ioctx_fsync (f->ioctx) < 0) {
+    if (ioctx_fsync (f->ioctx, datasync) < 0) {
         np_uerror (errno);
         goto error_quiet;
     }
diff --git a/src/libnpfs/9p.h b/src/libnpfs/9p.h
index 4d20c793..7912c642 100644
--- a/src/libnpfs/9p.h
+++ b/src/libnpfs/9p.h
@@ -445,6 +445,7 @@ struct p9_rreaddir {
 };
 struct p9_tfsync {
 	u32 fid;
+	u32 datasync;
 };
 struct p9_rfsync {
 };
diff --git a/src/libnpfs/fcall.c b/src/libnpfs/fcall.c
index 8eae19de..0e1f4f99 100644
--- a/src/libnpfs/fcall.c
+++ b/src/libnpfs/fcall.c
@@ -1045,7 +1045,7 @@ np_fsync(Npreq *req, Npfcall *tc)
 			np_uerror (ENOSYS);
 			goto done;
 		}
-		rc = (*req->conn->srv->fsync)(fid);
+		rc = (*req->conn->srv->fsync)(fid, tc->u.tfsync.datasync);
 	}
 done:
 	return rc;
diff --git a/src/libnpfs/np.c b/src/libnpfs/np.c
index b1bf42d2..267e2f04 100644
--- a/src/libnpfs/np.c
+++ b/src/libnpfs/np.c
@@ -1105,9 +1105,9 @@ np_create_treaddir(u32 fid, u64 offset, u32 count)
 }
 
 Npfcall *
-np_create_tfsync(u32 fid)
+np_create_tfsync(u32 fid, u32 datasync)
 {
-	int size = sizeof(u32);
+	int size = sizeof(u32) + sizeof(u32);
 	struct cbuf buffer;
 	struct cbuf *bufp = &buffer;
 	Npfcall *fc;
@@ -1115,6 +1115,7 @@ np_create_tfsync(u32 fid)
 	if (!(fc = np_create_common(bufp, size, P9_TFSYNC)))
 		return NULL;
 	buf_put_int32(bufp, fid, &fc->u.tfsync.fid);
+	buf_put_int32(bufp, datasync, &fc->u.tfsync.datasync);
 
 	return np_post_check(fc, bufp);
 }
@@ -1593,6 +1594,7 @@ np_deserialize(Npfcall *fc)
 		break;
 	case P9_TFSYNC:
 		fc->u.tfsync.fid = buf_get_int32(bufp);
+		fc->u.tfsync.datasync = buf_get_int32(bufp);
 		break;
 	case P9_RFSYNC:
 		break;
diff --git a/src/libnpfs/npfs.h b/src/libnpfs/npfs.h
index 8a399866..eb78cc50 100644
--- a/src/libnpfs/npfs.h
+++ b/src/libnpfs/npfs.h
@@ -309,7 +309,7 @@ struct Npsrv {
 	Npfcall*	(*xattrwalk)(Npfid *, Npfid *, Npstr *);
 	Npfcall*	(*xattrcreate)(Npfid *, Npstr *, u64, u32);
 	Npfcall*	(*readdir)(Npfid *, u64, u32, Npreq *);
-	Npfcall*	(*fsync)(Npfid *);
+	Npfcall*	(*fsync)(Npfid *, u32);
 	Npfcall*	(*llock)(Npfid *, u8, u32, u64, u64, u32, Npstr *);
 	Npfcall*	(*getlock)(Npfid *, u8 type, u64, u64, u32, Npstr *);
 	Npfcall*	(*link)(Npfid *, Npfid *, Npstr *);
@@ -472,7 +472,7 @@ Npfcall *np_create_rxattrcreate(void);
 Npfcall *np_create_treaddir(u32 fid, u64 offset, u32 count);
 Npfcall *np_create_rreaddir(u32 count);
 void np_finalize_rreaddir(Npfcall *fc, u32 count);
-Npfcall *np_create_tfsync(u32 fid);
+Npfcall *np_create_tfsync(u32 fid, u32 datasync);
 Npfcall *np_create_rfsync(void);
 Npfcall * np_create_tlock(u32 fid, u8 type, u32 flags, u64 start, u64 length,
 			  u32 proc_id, char *client_id);
diff --git a/tests/misc/t07.exp b/tests/misc/t07.exp
index cd87af7a..ba48fcf0 100644
--- a/tests/misc/t07.exp
+++ b/tests/misc/t07.exp
@@ -52,7 +52,7 @@ test_rreaddir(41): 92
 P9_RREADDIR tag 42 count 81
 01020000 00030000 00000000 00000000 00000000 00010300 61626304 05000000 
 06000000 00000000 32000000 00000000 02030064 65660708 00000009 00000000 
-test_tfsync(50): 11
+test_tfsync(50): 15
 P9_TFSYNC tag 42 fid 1
 test_rfsync(51): 7
 P9_RFSYNC tag 42
diff --git a/tests/misc/tserialize.c b/tests/misc/tserialize.c
index d1aab1ea..571fe7b5 100644
--- a/tests/misc/tserialize.c
+++ b/tests/misc/tserialize.c
@@ -644,11 +644,12 @@ test_tfsync (void)
 {
     Npfcall *fc, *fc2;
 
-    if (!(fc = np_create_tfsync(1)))
+    if (!(fc = np_create_tfsync(1, 42)))
         msg_exit ("out of memory");
     fc2 = _rcv_buf (fc, P9_TFSYNC,  __FUNCTION__);
 
-    assert (fc->u.tfsync.fid == fc2->u.treaddir.fid);
+    assert (fc->u.tfsync.fid == fc2->u.tfsync.fid);
+    assert (fc->u.tfsync.datasync == fc2->u.tfsync.datasync);
 
     free (fc);
     free (fc2);
diff --git a/tests/user/tflush.c b/tests/user/tflush.c
index aae0d6f4..d4b1970e 100644
--- a/tests/user/tflush.c
+++ b/tests/user/tflush.c
@@ -93,7 +93,8 @@ _flush_series (Npcfsys *fs, Npcfid *root)
         err_exit ("open)");
 
     for (i = 0; i < 100; i++) {
-        if (!(tc = np_create_tfsync (f->fid)))
+        // alternate with datasync set to 1 or 0
+        if (!(tc = np_create_tfsync (f->fid, i % 2 == 0 ? 0 : 1)))
             msg_exit ("out of memory");
         flushtag = tag = npc_get_id(fs->tagpool);
         np_set_tag(tc, tag);
@@ -115,7 +116,7 @@ _flush_series (Npcfsys *fs, Npcfid *root)
     msg ("sent 1 Tflush");
 
     for (i = 0; i < 100; i++) {
-        if (!(tc = np_create_tfsync (f->fid)))
+        if (!(tc = np_create_tfsync (f->fid, i % 2 == 0 ? 0 : 1)))
             msg_exit ("out of memory");
         tag = npc_get_id(fs->tagpool);
         np_set_tag(tc, tag);