Added "--discard" option.

doc/ACKNOWLEDGEMENTS.md

@@ -51,7 +51,7 @@ is acknowledged and greatly appreciated:
  * Kim Krecht - suggested buffer fill status and last bytes output display options
  * Cristian Ciupitu <http://ciupicri.github.io>, Josh Stone - pointed out file descriptor leak with helpful suggestions (Josh Stone initially noticed the missing close)
  * Jan Seda - found issue with `splice()` and *SPLICE_F_NONBLOCK* causing slowdown
- * André Stapf - pointed out formatting problem e.g. 13GB -> 13.1GB which should be shown 13.0GB -> 13.1GB; highlighted on-startup row swapping in "`-c`"
+ * André Stapf - pointed out formatting problem e.g. 13GB -> 13.1GB which should be shown 13.0GB -> 13.1GB; highlighted on-startup row swapping in "`-c`", and suggested "`--discard`"
  * Damon Harper <http://www.usrbin.ca/> - suggested "`-D`" / "`--delay-start`" option
  * Ganaël Laplanche <http://www.martymac.org> - provided patch for `lstat64()` on systems that do not support it
  * Peter Korsgaard <http://www.buildroot.net/> - provided similar patch for `lstat64()`, specifically for uClibc support; provided AIX cross-compilation patch to fix bug in "`-lc128`" check

doc/NEWS.md

@@ -2,6 +2,7 @@
 
   * feature: new "`--enable-static`" option to "`configure`" for static builds ([#75](https://codeberg.org/a-j-wood/pv/pull/75))
   * feature: now uses `posix_fadvise()` like `cat`(1) does, to improve efficiency ([#39](https://codeberg.org/a-j-wood/pv/issues/39))
+  * feature: new "`--discard`" option to discard input as if writing to */dev/null* ([#42](https://codeberg.org/a-j-wood/pv/issues/42))
   * security: with "`--pidfile`", write to a temporary file and rename it into place, to improve security
   * security: keep self-contained copies of name and format string in PV internal state for memory safety
   * fix: auto-calculate total line count with "`--line-mode`" when all inputs are regular files

doc/TODO.md

@@ -29,7 +29,6 @@ Feature requests
  * ([#38](https://codeberg.org/a-j-wood/pv/issues/38)) Reset ETA on *SIGUSR1* (Jacek Wielemborek - Jan 2019)
  * ([#40](https://codeberg.org/a-j-wood/pv/issues/40)) Permit "`-c`" with "`-d PID:FD`", reject "`-N`" with "`-d PID`" (Norman Rasmussen - Nov 2020)
  * ([#41](https://codeberg.org/a-j-wood/pv/issues/41)) Improve how backwards-moving reads are shown in "`--watchfd`" (Ryan Cooley - Dec 2017)
- * ([#42](https://codeberg.org/a-j-wood/pv/issues/42)) Option to discard stdin so nothing is written to stdout (André Stapf - Apr 2017)
  * ([#43](https://codeberg.org/a-j-wood/pv/issues/43)) Differentiate between "`--eta`" and "`--fineta`" in display (André Stapf - Apr 2017)
  * ([#45](https://codeberg.org/a-j-wood/pv/issues/45)) Option "`--sparse`" (with block size option) to write sparse output (Andriy Galetski - Apr 2019)
  * ([#46](https://codeberg.org/a-j-wood/pv/issues/46)) Option to show speed gauge (% max speed) if progress not known (Ryan Cooley - Jun 2019)

doc/pv.1

@@ -366,11 +366,14 @@ but means that the transfer buffer may not be used.  This prevents
 .B \-A
 and
 .B \-T
-from working, and makes
+from working, cannot work with
+.BR \-X ,
+and makes
 .B \-B
 redundant, so using
 .BR \-A ,
 .BR \-T ,
+.BR \-X ,
 or
 .B \-B
 automatically switches on
@@ -420,6 +423,15 @@ of filesystems in a single
 .B pv
 call.  Use this option with caution.
 .TP
+.B \-X, \-\-discard
+Instead of transferring input data to standard output, discard it.  This is
+equivalent to redirecting standard output to
+.IR /dev/null ,
+except that
+.BR write (2)
+is never called.  Implies
+.BR \-C .
+.TP
 .B \-d PID[:FD], \-\-watchfd PID[:FD]
 Instead of transferring data, watch file descriptor
 .B FD

src/include/options.h

@@ -45,6 +45,7 @@ struct opts_s {           /* structure describing run-time options */
 	bool stop_at_size;             /* set if we stop at "size" bytes */
 	bool sync_after_write;         /* set if we sync after every write */
 	bool direct_io;                /* set if O_DIRECT is to be used */
+	bool discard_input;            /* set to write nothing to stdout */
 	double interval;               /* interval between updates */
 	double delay_start;            /* delay before first display */
 	unsigned int watch_pid;	       /* process to watch fds of */

src/include/pv-internal.h

@@ -97,6 +97,7 @@ struct pvstate_s {
 	bool direct_io;                  /* set if O_DIRECT is to be used */
 	bool direct_io_changed;          /* set when direct_io is changed */
 	bool no_splice;                  /* never use splice() */
+	bool discard_input;              /* write nothing to stdout */
 	unsigned long long rate_limit;   /* rate limit, in bytes per second */
 	unsigned long long target_buffer_size;  /* buffer size (0=default) */
 	unsigned long long size;         /* total size of data */

src/include/pv.h

@@ -116,6 +116,7 @@ extern void pv_state_direct_io_set(pvstate_t, bool);
 extern void pv_state_rate_limit_set(pvstate_t, unsigned long long);
 extern void pv_state_target_buffer_size_set(pvstate_t, unsigned long long);
 extern void pv_state_no_splice_set(pvstate_t, bool);
+extern void pv_state_discard_input_set(pvstate_t, bool);
 extern void pv_state_size_set(pvstate_t, unsigned long long);
 extern void pv_state_interval_set(pvstate_t, double);
 extern void pv_state_width_set(pvstate_t, unsigned int);

src/main/help.c

@@ -377,6 +377,9 @@ void display_help(void)
 		{ "-K", "--direct-io", NULL,
 		 N_("use direct I/O to bypass cache"),
 		 { 0, 0, 0, 0} },
+		{ "-X", "--discard", NULL,
+		 N_("discard input instead of writing to output"),
+		 { 0, 0, 0, 0} },
 #ifdef HAVE_IPC
 		{ "-R", "--remote", N_("PID"),
 		 N_("update settings of process PID"),

src/main/main.c

@@ -273,6 +273,7 @@ int main(int argc, char **argv)
 	pv_state_stop_at_size_set(state, opts->stop_at_size);
 	pv_state_sync_after_write_set(state, opts->sync_after_write);
 	pv_state_direct_io_set(state, opts->direct_io);
+	pv_state_discard_input_set(state, opts->discard_input);
 	pv_state_rate_limit_set(state, opts->rate_limit);
 	pv_state_target_buffer_size_set(state, opts->buffer_size);
 	pv_state_no_splice_set(state, opts->no_splice);

src/main/options.c

@@ -172,6 +172,7 @@ 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' },
+		{ "discard", 0, NULL, (int) 'X' },
 		{ "remote", 1, NULL, (int) 'R' },
 		{ "pidfile", 1, NULL, (int) 'P' },
 		{ "watchfd", 1, NULL, (int) 'd' },
@@ -184,7 +185,7 @@ opts_t opts_parse(unsigned int argc, char **argv)
 	/*@+nullassign@ */
 	int option_index = 0;
 #endif				/* HAVE_GETOPT_LONG */
-	char *short_options = "hVpteIrab8TA:fnqcWD:s:l0i:w:H:N:F:L:B:CESYKR:P:d:m:"
+	char *short_options = "hVpteIrab8TA:fnqcWD:s:l0i:w:H:N:F:L:B:CESYKXR:P:d:m:"
 #ifdef ENABLE_DEBUGGING
 	    "!:"
 #endif
@@ -464,6 +465,10 @@ opts_t opts_parse(unsigned int argc, char **argv)
 		case 'K':
 			opts->direct_io = true;
 			break;
+		case 'X':
+			opts->discard_input = true;
+			opts->no_splice = true;
+			break;
 		case 'R':
 			opts->remote = pv_getnum_ui(optarg);
 			break;

src/pv/state.c

@@ -223,6 +223,11 @@ void pv_state_direct_io_set(pvstate_t state, bool val)
 	state->direct_io_changed = true;
 };
 
+void pv_state_discard_input_set(pvstate_t state, bool val)
+{
+	state->discard_input = val;
+};
+
 void pv_state_rate_limit_set(pvstate_t state, unsigned long long val)
 {
 	state->rate_limit = val;

src/pv/transfer.c

@@ -493,19 +493,23 @@ static int pv__transfer_read(pvstate_t state, int fd, int *eof_in, int *eof_out,
  *
  * On error, sets *eof_out to 1, sets state->written to -1, and updates
  * state->exit_status.
+ *
+ * If state->discard_input is true, does not actually write anything.
  */
 static int pv__transfer_write(pvstate_t state, int *eof_in, int *eof_out, long *lineswritten)
 {
 	ssize_t nwritten;
 
-	signal(SIGALRM, SIG_IGN);
-	alarm(1);
-
-	nwritten = pv__transfer_write_repeated(STDOUT_FILENO,
-					       state->transfer_buffer +
-					       state->write_position, state->to_write, state->sync_after_write);
-
-	alarm(0);
+	if (state->discard_input) {
+		nwritten = state->to_write;
+	} else {
+		signal(SIGALRM, SIG_IGN);
+		alarm(1);
+		nwritten = pv__transfer_write_repeated(STDOUT_FILENO,
+						       state->transfer_buffer +
+						       state->write_position, state->to_write, state->sync_after_write);
+		alarm(0);
+	}
 
 	if (0 == nwritten) {
 		/*