gpiomon: add option to set line buffered output

Some applications call gpiomon in a sub process, in which case glibc
defaults to block buffered output on stdout. This makes the output
arrive to the calling process only when the (4kB) buffer is filled (or
when gpiomon exists), making the information obsolete and pretty much
useless.

Support such scenarios by adding a switch to configure line buffered
output on stdout. Similar switches are available in other applications
(e.g. `rsync`s --output argument).

Signed-off-by: Martin Hundebøll <martin@geanix.com>
[Bartosz:
  - use setlinebuf() instead of setvbuf(),
  - tweak the help string,
  - move the setlinebuf() call directly into the optarg switch statement]
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

diff --git a/src/tools/gpiomon.c b/src/tools/gpiomon.c
index 0d5fcbde4f53d129811f31bff55acd914c097791..9a1843b64ec81cf67aad81911a93f9875cf5e70e 100644 (file)
--- a/src/tools/gpiomon.c
+++ b/src/tools/gpiomon.c
@@ -26,17 +26,18 @@ static const struct option longopts[] = {
        { "silent",             no_argument,            NULL,   's' },
        { "rising-edge",        no_argument,            NULL,   'r' },
        { "falling-edge",       no_argument,            NULL,   'f' },
+       { "line-buffered",      no_argument,            NULL,   'b' },
        { "format",             required_argument,      NULL,   'F' },
        { GETOPT_NULL_LONGOPT },
 };
 
-static const char *const shortopts = "+hvln:srfF:";
+static const char *const shortopts = "+hvln:srfbF:";
 
 static void print_help(void)
 {
        printf("Usage: %s [OPTIONS] <chip name/number> <offset 1> <offset 2> ...\n",
               get_progname());
-       printf("Wait for events on GPIO lines\n");
+       printf("Wait for events on GPIO lines and print them to standard output\n");
        printf("\n");
        printf("Options:\n");
        printf("  -h, --help:\t\tdisplay this message and exit\n");
@@ -46,6 +47,7 @@ static void print_help(void)
        printf("  -s, --silent:\t\tdon't print event info\n");
        printf("  -r, --rising-edge:\tonly process rising edge events\n");
        printf("  -f, --falling-edge:\tonly process falling edge events\n");
+       printf("  -b, --line-buffered:\tset standard output as line buffered\n");
        printf("  -F, --format=FMT\tspecify custom output format\n");
        printf("\n");
        printf("Format specifiers:\n");
@@ -278,6 +280,9 @@ int main(int argc, char **argv)
                case 'f':
                        watch_falling = true;
                        break;
+               case 'b':
+                       setlinebuf(stdout);
+                       break;
                case 'F':
                        ctx.fmt = optarg;
                        break;