extend --sync to allow {sync,dsync,0,1}, to support O_DSYNC

Fixes: axboe#1033

HOWTO

@@ -1677,10 +1677,28 @@ Buffers and memory
 	This will be ignored if :option:`pre_read` is also specified for the
 	same job.
 
-.. option:: sync=bool
+.. option:: sync=str
+
+	Whether, and what type, of synchronous I/O to use for writes.  The allowed
+	values are:
+
+		**none**
+			Do not use synchronous IO, the default.
+
+		**0**
+			Same as **none**.
+
+		**sync**
+			Use synchronous file IO. For the majority of I/O engines,
+			this means using O_SYNC.
+
+		**1**
+			Same as **sync**.
+
+		**dsync**
+			Use synchronous data IO. For the majority of I/O engines,
+			this means using O_DSYNC.
 
-	Use synchronous I/O for buffered writes. For the majority of I/O engines,
-	this means using O_SYNC. Default: false.
 
 .. option:: iomem=str, mem=str
 

engines/glusterfs.c

@@ -271,8 +271,7 @@ int fio_gf_open_file(struct thread_data *td, struct fio_file *f)
 
 	if (td->o.odirect)
 		flags |= OS_O_DIRECT;
-	if (td->o.sync_io)
-		flags |= O_SYNC;
+	flags |= td->o.sync_io;
 
 	dprint(FD_FILE, "fio file %s open mode %s td rw %s\n", f->file_name,
 	       flags & O_RDONLY ? "ro" : "rw", td_read(td) ? "read" : "write");

engines/ime.c

@@ -194,8 +194,7 @@ static int fio_ime_open_file(struct thread_data *td, struct fio_file *f)
 	}
 	if (td->o.odirect)
 		flags |= O_DIRECT;
-	if (td->o.sync_io)
-		flags |= O_SYNC;
+	flags |= td->o.sync_io;
 	if (td->o.create_on_open && td->o.allow_create)
 		flags |= O_CREAT;
 

engines/libpmem.c

@@ -193,6 +193,7 @@ static enum fio_q_status fio_libpmem_queue(struct thread_data *td,
 
 	dprint(FD_IO, "DEBUG fio_libpmem_queue\n");
 	dprint(FD_IO,"td->o.odirect %d td->o.sync_io %d \n",td->o.odirect, td->o.sync_io);
+	/* map both O_SYNC / DSYNC to not using NODRAIN */
 	flags = td->o.sync_io ? 0 : PMEM_F_MEM_NODRAIN;
 	flags |= td->o.odirect ? PMEM_F_MEM_NONTEMPORAL : PMEM_F_MEM_TEMPORAL;
 

filesetup.c

@@ -655,8 +655,7 @@ int generic_open_file(struct thread_data *td, struct fio_file *f)
 		}
 		flags |= OS_O_DIRECT | FIO_O_ATOMIC;
 	}
-	if (td->o.sync_io)
-		flags |= O_SYNC;
+	flags |= td->o.sync_io;
 	if (td->o.create_on_open && td->o.allow_create)
 		flags |= O_CREAT;
 skip_flags:

fio.1

@@ -1462,9 +1462,31 @@ starting I/O if the platform and file type support it. Defaults to true.
 This will be ignored if \fBpre_read\fR is also specified for the
 same job.
 .TP
-.BI sync \fR=\fPbool
-Use synchronous I/O for buffered writes. For the majority of I/O engines,
-this means using O_SYNC. Default: false.
+.BI sync \fR=\fPstr
+Whether, and what type, of synchronous I/O to use for writes.  The allowed
+values are:
+.RS
+.RS
+.TP
+.B none
+Do not use synchronous IO, the default.
+.TP
+.B 0
+Same as \fBnone\fR.
+.TP
+.B sync
+Use synchronous file IO. For the majority of I/O engines,
+this means using O_SYNC.
+.TP
+.B 1
+Same as \fBsync\fR.
+.TP
+.B dsync
+Use synchronous data IO. For the majority of I/O engines,
+this means using O_DSYNC.
+.PD
+.RE
+.RE
 .TP
 .BI iomem \fR=\fPstr "\fR,\fP mem" \fR=\fPstr
 Fio can use various types of memory as the I/O unit buffer. The allowed

options.c

@@ -3733,14 +3733,32 @@ struct fio_option fio_options[FIO_MAX_OPTS] = {
 	{
 		.name	= "sync",
 		.lname	= "Synchronous I/O",
-		.type	= FIO_OPT_BOOL,
+		.type	= FIO_OPT_STR,
 		.off1	= offsetof(struct thread_options, sync_io),
-		.help	= "Use O_SYNC for buffered writes",
-		.def	= "0",
-		.parent = "buffered",
+		.help	= "Use synchronous write IO",
+		.def	= "none",
 		.hide	= 1,
 		.category = FIO_OPT_C_IO,
 		.group	= FIO_OPT_G_IO_TYPE,
+		.posval = {
+			  { .ival = "none",
+			    .oval = 0,
+			  },
+			  { .ival = "0",
+			    .oval = 0,
+			  },
+			  { .ival = "sync",
+			    .oval = O_SYNC,
+			  },
+			  { .ival = "1",
+			    .oval = O_SYNC,
+			  },
+#ifdef O_DSYNC
+			  { .ival = "dsync",
+			    .oval = O_DSYNC,
+			  },
+#endif
+		},
 	},
 #ifdef FIO_HAVE_WRITE_HINT
 	{