Add a "fillchar" command line argument to dd(1) that permits the user

to specify an alternative padding character when using a conversion
mode, or when using noerror with sync and an input error occurs.  This
facilities reading old and error-prone media by allowing the user to
more effectively mark error blocks in the output stream.

5 files changed, 32 insertions, 2 deletions

diff --git a/bin/dd/args.c b/bin/dd/args.c
index c4d418b..161fbfc 100644
--- a/bin/dd/args.c
+++ b/bin/dd/args.c
@@ -58,6 +58,7 @@ static void	f_cbs(char *);
 static void	f_conv(char *);
 static void	f_count(char *);
 static void	f_files(char *);
+static void	f_fillchar(char *);
 static void	f_ibs(char *);
 static void	f_if(char *);
 static void	f_obs(char *);
@@ -77,6 +78,7 @@ static const struct arg {
 	{ "conv",	f_conv,		0,	 0 },
 	{ "count",	f_count,	C_COUNT, C_COUNT },
 	{ "files",	f_files,	C_FILES, C_FILES },
+	{ "fillchar",	f_fillchar,	C_FILL,	 C_FILL },
 	{ "ibs",	f_ibs,		C_IBS,	 C_BS|C_IBS },
 	{ "if",		f_if,		C_IF,	 C_IF },
 	{ "iseek",	f_skip,		C_SKIP,	 C_SKIP },
@@ -224,6 +226,16 @@ f_files(char *arg)
 }
 
 static void
+f_fillchar(char *arg)
+{
+
+	if (strlen(arg) != 1)
+		errx(1, "need exactly one fill char");
+
+	fill_char = arg[0];
+}
+
+static void
 f_ibs(char *arg)
 {
 	uintmax_t res;
diff --git a/bin/dd/dd.1 b/bin/dd/dd.1
index 1cbe499..6f3298e 100644
--- a/bin/dd/dd.1
+++ b/bin/dd/dd.1
@@ -84,6 +84,13 @@ Copy
 .Ar n
 input files before terminating.
 This operand is only applicable when the input device is a tape.
+.It Cm fillchar Ns = Ns Ar c
+When padding a block in conversion mode or due to use of
+.Cm noerror
+and
+.Cm sync
+modes, fill with the specified ASCII character, rather than using a space
+or nul.
 .It Cm ibs Ns = Ns Ar n
 Set the input block size to
 .Ar n
@@ -247,6 +254,10 @@ with
 bytes (or with spaces if a block oriented conversion value was
 specified) and processed as a normal input buffer.
 If the
+.Cm fillchar
+option is specified, the fill char provided on the command line will override
+the automatic selection of fill character.
+If the
 .Cm sync
 conversion is not specified, the input block is omitted from the output.
 On input files which are not tapes or pipes, the file offset
diff --git a/bin/dd/dd.c b/bin/dd/dd.c
index 678f138..0bb43f7 100644
--- a/bin/dd/dd.c
+++ b/bin/dd/dd.c
@@ -80,6 +80,7 @@ u_int	ddflags = 0;		/* conversion options */
 size_t	cbsz;			/* conversion block size */
 uintmax_t files_cnt = 1;	/* # of files to copy */
 const	u_char *ctab;		/* conversion table */
+char	fill_char;		/* Character to fill with if defined */
 
 int
 main(int argc __unused, char *argv[])
@@ -287,7 +288,9 @@ dd_in(void)
 		 * use spaces.
 		 */
 		if (ddflags & C_SYNC) {
-			if (ddflags & (C_BLOCK | C_UNBLOCK))
+			if (ddflags & C_FILL)
+				memset(in.dbp, fill_char, in.dbsz);
+			else if (ddflags & (C_BLOCK | C_UNBLOCK))
 				memset(in.dbp, ' ', in.dbsz);
 			else
 				memset(in.dbp, 0, in.dbsz);
@@ -382,7 +385,9 @@ dd_close(void)
 	else if (cfunc == unblock)
 		unblock_close();
 	if (ddflags & C_OSYNC && out.dbcnt && out.dbcnt < out.dbsz) {
-		if (ddflags & (C_BLOCK | C_UNBLOCK))
+		if (ddflags & C_FILL)
+			memset(out.dbp, fill_char, out.dbsz - out.dbcnt);
+		else if (ddflags & (C_BLOCK | C_UNBLOCK))
 			memset(out.dbp, ' ', out.dbsz - out.dbcnt);
 		else
 			memset(out.dbp, 0, out.dbsz - out.dbcnt);
diff --git a/bin/dd/dd.h b/bin/dd/dd.h
index b89335b..ad283fd 100644
--- a/bin/dd/dd.h
+++ b/bin/dd/dd.h
@@ -94,5 +94,6 @@ typedef struct {
 #define	C_SYNC		0x8000000
 #define	C_UCASE		0x10000000
 #define	C_UNBLOCK	0x20000000
+#define	C_FILL		0x40000000
 
 #define	C_PARITY	(C_PAREVEN | C_PARODD | C_PARNONE | C_PARSET)
diff --git a/bin/dd/extern.h b/bin/dd/extern.h
index 8b3ca09..9c540ad 100644
--- a/bin/dd/extern.h
+++ b/bin/dd/extern.h
@@ -60,3 +60,4 @@ extern const u_char a2e_32V[], a2e_POSIX[];
 extern const u_char e2a_32V[], e2a_POSIX[];
 extern const u_char a2ibm_32V[], a2ibm_POSIX[];
 extern u_char casetab[];
+extern char fill_char;