Add --sparse / -O to the manual, to --help, and to option processing (#45).

docs/pv.1

@@ -273,9 +273,9 @@ from or to a pipe than regular \fBread\fR(2) and \fBwrite\fR(2), but means
 that the transfer buffer may not be used.
 This prevents \*(lq\fB\-\-buffer\-percent\fR\*(rq and
 \*(lq\fB\-\-last\-written\fR\*(rq from working, cannot work with
-\*(lq\fB\-\-discard\fR\*(rq, and makes \*(lq\fB\-\-buffer\-size\fR\*(rq
-redundant, so using any of those options automatically switches on
-\*(lq\fB\-\-no\-splice\fR\*(rq.
+\*(lq\fB\-\-sparse\fR\*(rq or \*(lq\fB\-\-discard\fR\*(rq, and makes
+\*(lq\fB\-\-buffer\-size\fR\*(rq redundant, so using any of those options
+automatically switches on \*(lq\fB\-\-no\-splice\fR\*(rq.
 Switching on this option results in a small loss of transfer efficiency.
 It has no effect on systems where \fBsplice\fR(2) is unavailable.
 .TP
@@ -325,6 +325,13 @@ failures with an error of \*(lqInvalid argument\*(rq, especially if reading
 and writing files across a variety of filesystems in a single \fBpv\fR call.
 Use this option with caution.
 .TP
+.B \-O, \-\-sparse
+When writing null bytes, try to seek, producing a sparse output file.
+Implies \*(lq\fB\-\-no\-splice\fR\*(rq.
+On filesystems without sparse file support, or when the output is not
+seekable, this option will have no effect other than to turn on
+\*(lq\fB\-\-no\-splice\fR\*(rq.
+.TP
 .B \-X, \-\-discard
 Instead of transferring input data to standard output, discard it.
 This is equivalent to redirecting standard output to \fI/dev/null\fR,

docs/pv.1.md

@@ -281,11 +281,11 @@ are explicitly switched on will be shown.
     data from or to a pipe than regular **read**(2) and **write**(2),
     but means that the transfer buffer may not be used. This prevents
     "**\--buffer-percent**" and "**\--last-written**" from working,
-    cannot work with "**\--discard**", and makes "**\--buffer-size**"
-    redundant, so using any of those options automatically switches on
-    "**\--no-splice**". Switching on this option results in a small loss
-    of transfer efficiency. It has no effect on systems where
-    **splice**(2) is unavailable.
+    cannot work with "**\--sparse**" or "**\--discard**", and makes
+    "**\--buffer-size**" redundant, so using any of those options
+    automatically switches on "**\--no-splice**". Switching on this
+    option results in a small loss of transfer efficiency. It has no
+    effect on systems where **splice**(2) is unavailable.
 
 **-E, \--skip-errors**
 
@@ -336,6 +336,13 @@ are explicitly switched on will be shown.
     especially if reading and writing files across a variety of
     filesystems in a single **pv** call. Use this option with caution.
 
+**-O, \--sparse**
+
+:   When writing null bytes, try to seek, producing a sparse output
+    file. Implies "**\--no-splice**". On filesystems without sparse file
+    support, or when the output is not seekable, this option will have
+    no effect other than to turn on "**\--no-splice**".
+
 **-X, \--discard**
 
 :   Instead of transferring input data to standard output, discard it.

src/main/help.c

@@ -351,6 +351,9 @@ void display_help(void)
 		{ "-K", "--direct-io", NULL,
 		 N_("use direct I/O to bypass cache"),
 		 { 0, 0, 0, 0} },
+		{ "-O", "--sparse", NULL,
+		 N_("try to seek instead of writing null bytes"),
+		 { 0, 0, 0, 0} },
 		{ "-X", "--discard", NULL,
 		 N_("discard input instead of writing to output"),
 		 { 0, 0, 0, 0} },

src/main/options.c

@@ -612,6 +612,8 @@ opts_t opts_parse(unsigned int argc, char **argv)
 		{ "stop-at-size", 0, NULL, (int) 'S' },
 		{ "sync", 0, NULL, (int) 'Y' },
 		{ "direct-io", 0, NULL, (int) 'K' },
+		{ "sparse", 0, NULL, (int) 'O' },
+		{ "sparse-output", 0, NULL, (int) 'O' },
 		{ "discard", 0, NULL, (int) 'X' },
 		{ "store-and-forward", 1, NULL, (int) 'U' },
 		{ "remote", 1, NULL, (int) 'R' },
@@ -627,7 +629,7 @@ opts_t opts_parse(unsigned int argc, char **argv)
 	/*@+nullassign@ */
 	int option_index = 0;
 #endif				/* HAVE_GETOPT_LONG */
-	char *short_options = "hVpteIrab8kTA:fvnqcWD:s:gl0i:w:H:N:u:F:x:L:B:CEZ:SYKXU:R:P:d:m:o:"
+	char *short_options = "hVpteIrab8kTA:fvnqcWD:s:gl0i:w:H:N:u:F:x:L:B:CEZ:SYKOXU:R:P:d:m:o:"
 #ifdef ENABLE_DEBUGGING
 	    "!:"
 #endif
@@ -972,6 +974,10 @@ opts_t opts_parse(unsigned int argc, char **argv)
 		case 'K':
 			opts->direct_io = true;
 			break;
+		case 'O':
+			opts->sparse_output = true;
+			opts->no_splice = true;
+			break;
 		case 'X':
 			opts->discard_input = true;
 			opts->no_splice = true;