sync: add support for -d -f FILE

Based on the patch by Ari Sundholm <ari@tuxera.com>

function                                             old     new   delta
sync_main                                             20     163    +143
packed_usage                                       30653   30673     +20
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 163/0)             Total: 163 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/Config.src

@@ -571,12 +571,6 @@ config SUM
 	help
 	  checksum and count the blocks in a file
 
-config SYNC
-	bool "sync"
-	default y
-	help
-	  sync is used to flush filesystem buffers.
-
 config TAC
 	bool "tac"
 	default y

coreutils/Kbuild.src

@@ -68,7 +68,6 @@ lib-$(CONFIG_SORT)      += sort.o
 lib-$(CONFIG_STAT)      += stat.o
 lib-$(CONFIG_STTY)      += stty.o
 lib-$(CONFIG_SUM)       += sum.o
-lib-$(CONFIG_SYNC)      += sync.o
 lib-$(CONFIG_TAC)       += tac.o
 lib-$(CONFIG_TEE)       += tee.o
 lib-$(CONFIG_TRUE)      += true.o

coreutils/sync.c

@@ -3,16 +3,39 @@
  * Mini sync implementation for busybox
  *
  * Copyright (C) 1995, 1996 by Bruce Perens <bruce@pixar.com>.
+ * Copyright (C) 2015 by Ari Sundholm <ari@tuxera.com>
  *
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 
 /* BB_AUDIT SUSv3 N/A -- Matches GNU behavior. */
+//config:config SYNC
+//config:	bool "sync"
+//config:	default y
+//config:	help
+//config:	  sync is used to flush filesystem buffers.
+//config:config FEATURE_SYNC_FANCY
+//config:	bool "Enable -d and -f flags (requres syncfs(2) in libc)"
+//config:	default y
+//config:	depends on SYNC
+//config:	help
+//config:	  sync -d FILE... executes fdatasync() on each FILE.
+//config:	  sync -f FILE... executes syncfs() on each FILE.
+
+//kbuild:lib-$(CONFIG_SYNC) += sync.o
+//applet:IF_SYNC(APPLET_NOFORK(sync, sync, BB_DIR_BIN, BB_SUID_DROP, sync))
 
 //usage:#define sync_trivial_usage
-//usage:       ""
+//usage:       ""IF_FEATURE_SYNC_FANCY("[-df] [FILE]...")
 //usage:#define sync_full_usage "\n\n"
+//usage:    IF_NOT_FEATURE_SYNC_FANCY(
 //usage:       "Write all buffered blocks to disk"
+//usage:    )
+//usage:    IF_FEATURE_SYNC_FANCY(
+//usage:       "Write all buffered blocks (in FILEs) to disk"
+//usage:     "\n	-d	Avoid syncing metadata"
+//usage:     "\n	-f	Sync filesystems underlying FILEs"
+//usage:    )
 
 #include "libbb.h"
 
@@ -21,10 +44,59 @@
 int sync_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int sync_main(int argc UNUSED_PARAM, char **argv IF_NOT_DESKTOP(UNUSED_PARAM))
 {
+#if !ENABLE_FEATURE_SYNC_FANCY
 	/* coreutils-6.9 compat */
 	bb_warn_ignoring_args(argv[1]);
-
 	sync();
-
 	return EXIT_SUCCESS;
+#else
+	unsigned opts;
+	int ret = EXIT_SUCCESS;
+
+	enum {
+		OPT_DATASYNC = (1 << 0),
+		OPT_SYNCFS   = (1 << 1),
+	};
+
+	opt_complementary = "d--f:f--d";
+	opts = getopt32(argv, "df");
+	argv += optind;
+
+	/* Handle the no-argument case. */
+	if (!argv[0])
+		sync();
+
+	while (*argv) {
+		int fd = open_or_warn(*argv, O_RDONLY);
+
+		if (fd < 0) {
+			ret = EXIT_FAILURE;
+			goto next;
+		}
+		if (opts & OPT_DATASYNC) {
+			if (fdatasync(fd))
+				goto err;
+			goto do_close;
+		}
+		if (opts & OPT_SYNCFS) {
+			/*
+			 * syncfs is documented to only fail with EBADF,
+			 * which can't happen here. So, no error checks.
+			 */
+			syncfs(fd);
+			goto do_close;
+		}
+		if (fsync(fd)) {
+ err:
+			bb_simple_perror_msg(*argv);
+			ret = EXIT_FAILURE;
+		}
+ do_close:
+		close(fd);
+ next:
+		++argv;
+	}
+
+	return ret;
+#endif
 }

include/applets.src.h

@@ -337,7 +337,6 @@ IF_SVLOGD(APPLET(svlogd, BB_DIR_USR_SBIN, BB_SUID_DROP))
 IF_SWAPONOFF(APPLET_ODDNAME(swapoff, swap_on_off, BB_DIR_SBIN, BB_SUID_DROP, swapoff))
 IF_SWAPONOFF(APPLET_ODDNAME(swapon, swap_on_off, BB_DIR_SBIN, BB_SUID_DROP, swapon))
 IF_SWITCH_ROOT(APPLET(switch_root, BB_DIR_SBIN, BB_SUID_DROP))
-IF_SYNC(APPLET_NOFORK(sync, sync, BB_DIR_BIN, BB_SUID_DROP, sync))
 IF_BB_SYSCTL(APPLET(sysctl, BB_DIR_SBIN, BB_SUID_DROP))
 IF_SYSLOGD(APPLET(syslogd, BB_DIR_SBIN, BB_SUID_DROP))
 IF_TAC(APPLET_NOEXEC(tac, tac, BB_DIR_USR_BIN, BB_SUID_DROP, tac))