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>

3 files changed, 75 insertions, 10 deletions

diff --git a/coreutils/Config.src b/coreutils/Config.src
index 1ec3a0a99..02155d220 100644
--- a/coreutils/Config.src
+++ b/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
diff --git a/coreutils/Kbuild.src b/coreutils/Kbuild.src
index ec4ef7df2..4ec075ac6 100644
--- a/coreutils/Kbuild.src
+++ b/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
diff --git a/coreutils/sync.c b/coreutils/sync.c
index 7d98a1e30..974e90452 100644
--- a/coreutils/sync.c
+++ b/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
 }