dd: add 'oflag=seek_bytes'

Allow specifying position in the output file in bytes instead of
obs-sized blocks, improve compatibility with GNU dd.

function                                             old     new   delta
dd_main                                             1632    1693     +61
packed_usage                                       33130   33150     +20
static.oflag_words                                     -      12     +12
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/0 up/down: 93/0)               Total: 93 bytes

Signed-off-by: Rostislav Skudnov <rostislav@tuxera.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/dd.c

@@ -37,7 +37,7 @@
 //config:	elapsed time and speed.
 //config:
 //config:config FEATURE_DD_IBS_OBS
-//config:	bool "Enable ibs, obs, iflag and conv options"
+//config:	bool "Enable ibs, obs, iflag, oflag and conv options"
 //config:	default y
 //config:	depends on DD
 //config:	help
@@ -57,7 +57,7 @@
 
 //usage:#define dd_trivial_usage
 //usage:       "[if=FILE] [of=FILE] " IF_FEATURE_DD_IBS_OBS("[ibs=N] [obs=N] ") "[bs=N] [count=N] [skip=N]\n"
-//usage:       "	[seek=N]" IF_FEATURE_DD_IBS_OBS(" [conv=notrunc|noerror|sync|fsync] [iflag=skip_bytes|fullblock]")
+//usage:       "	[seek=N]" IF_FEATURE_DD_IBS_OBS(" [conv=notrunc|noerror|sync|fsync] [iflag=skip_bytes|fullblock] [oflag=seek_bytes]")
 //usage:#define dd_full_usage "\n\n"
 //usage:       "Copy a file with converting and formatting\n"
 //usage:     "\n	if=FILE		Read from FILE instead of stdin"
@@ -80,6 +80,7 @@
 //usage:     "\n	conv=swab	Swap every pair of bytes"
 //usage:     "\n	iflag=skip_bytes	skip=N is in bytes"
 //usage:     "\n	iflag=fullblock	Read full blocks"
+//usage:     "\n	oflag=seek_bytes	seek=N is in bytes"
 //usage:	)
 //usage:	IF_FEATURE_DD_STATUS(
 //usage:     "\n	status=noxfer	Suppress rate output"
@@ -133,10 +134,14 @@ enum {
 	FLAG_SKIP_BYTES = (1 << 5) * ENABLE_FEATURE_DD_IBS_OBS,
 	FLAG_FULLBLOCK = (1 << 6) * ENABLE_FEATURE_DD_IBS_OBS,
 	/* end of input flags */
-	FLAG_TWOBUFS = (1 << 7) * ENABLE_FEATURE_DD_IBS_OBS,
-	FLAG_COUNT   = 1 << 8,
-	FLAG_STATUS_NONE = 1 << 9,
-	FLAG_STATUS_NOXFER = 1 << 10,
+	/* start of output flags */
+	FLAG_OFLAG_SHIFT = 7,
+	FLAG_SEEK_BYTES = (1 << 7) * ENABLE_FEATURE_DD_IBS_OBS,
+	/* end of output flags */
+	FLAG_TWOBUFS = (1 << 8) * ENABLE_FEATURE_DD_IBS_OBS,
+	FLAG_COUNT   = 1 << 9,
+	FLAG_STATUS_NONE = 1 << 10,
+	FLAG_STATUS_NOXFER = 1 << 11,
 };
 
 static void dd_output_status(int UNUSED_PARAM cur_signal)
@@ -250,7 +255,7 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 	static const char keywords[] ALIGN1 =
 		"bs\0""count\0""seek\0""skip\0""if\0""of\0"IF_FEATURE_DD_STATUS("status\0")
 #if ENABLE_FEATURE_DD_IBS_OBS
-		"ibs\0""obs\0""conv\0""iflag\0"
+		"ibs\0""obs\0""conv\0""iflag\0""oflag\0"
 #endif
 		;
 #if ENABLE_FEATURE_DD_IBS_OBS
@@ -258,6 +263,8 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 		"notrunc\0""sync\0""noerror\0""fsync\0""swab\0";
 	static const char iflag_words[] ALIGN1 =
 		"skip_bytes\0""fullblock\0";
+	static const char oflag_words[] ALIGN1 =
+		"seek_bytes\0";
 #endif
 #if ENABLE_FEATURE_DD_STATUS
 	static const char status_words[] ALIGN1 =
@@ -276,6 +283,7 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 		OP_obs,
 		OP_conv,
 		OP_iflag,
+		OP_oflag,
 		/* Must be in the same order as FLAG_XXX! */
 		OP_conv_notrunc = 0,
 		OP_conv_sync,
@@ -297,6 +305,7 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 	//swab          swap every pair of input bytes: will abort on non-even reads
 		OP_iflag_skip_bytes,
 		OP_iflag_fullblock,
+		OP_oflag_seek_bytes,
 #endif
 	};
 	smallint exitcode = EXIT_FAILURE;
@@ -368,6 +377,10 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 			G.flags |= parse_comma_flags(val, iflag_words, "iflag") << FLAG_IFLAG_SHIFT;
 			/*continue;*/
 		}
+		if (what == OP_oflag) {
+			G.flags |= parse_comma_flags(val, oflag_words, "oflag") << FLAG_OFLAG_SHIFT;
+			/*continue;*/
+		}
 #endif
 		if (what == OP_bs) {
 			ibs = xatoul_range_sfx(val, 1, ((size_t)-1L)/2, cwbkMG_suffixes);
@@ -439,7 +452,8 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 		xmove_fd(xopen(outfile, oflag), ofd);
 
 		if (seek && !(G.flags & FLAG_NOTRUNC)) {
-			if (ftruncate(ofd, seek * obs) < 0) {
+			size_t blocksz = (G.flags & FLAG_SEEK_BYTES) ? 1 : obs;
+			if (ftruncate(ofd, seek * blocksz) < 0) {
 				struct stat st;
 
 				if (fstat(ofd, &st) < 0
@@ -472,7 +486,8 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 		}
 	}
 	if (seek) {
-		if (lseek(ofd, seek * obs, SEEK_CUR) < 0)
+		size_t blocksz = (G.flags & FLAG_SEEK_BYTES) ? 1 : obs;
+		if (lseek(ofd, seek * blocksz, SEEK_CUR) < 0)
 			goto die_outfile;
 	}
 

docs/posix_conformance.txt

@@ -182,6 +182,7 @@ dd compatibility options:
   conv=fsync      |  yes   |           |
   iflag=skip_bytes|  yes   |           |
   iflag=fullblock |  yes   |           |
+  oflag=seek_bytes|  yes   |           |
 
 df POSIX options
  option           | exists | compliant | remarks