From 7243cbb27d98d9f346877319e9697ad126b1425e Mon Sep 17 00:00:00 2001
From: Fredrik Tolf <fredrik@dolda2000.com>
Date: Fri, 14 Sep 2018 20:51:18 +0200
Subject: [PATCH] gpio: Auto-export ports.

---
 gpio.c | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/gpio.c b/gpio.c
index 1d8b322..0179c18 100644
--- a/gpio.c
+++ b/gpio.c
@@ -17,6 +17,7 @@ static const int imap[] = {
 };
 static const int *umap = bmap;
 static int mapn = sizeof(bmap) / sizeof(*bmap);
+static int preserve = 0;
 
 static int mappin(int num)
 {
@@ -25,22 +26,47 @@ static int mappin(int num)
     return(umap[num]);
 }
 
+static void export(int p)
+{
+    char path[256];
+    FILE *fp;
+    int rp;
+    
+    if((rp = mappin(p)) < 0)
+	errx(1, "%i: no such port\n", p);
+    sprintf(path, "/sys/class/gpio/gpio%i", rp);
+    if(!access(path, R_OK | X_OK))
+	return;
+    if(preserve)
+	errx(2, "gpio%i: not exported", rp);
+    sprintf(path, "/sys/class/gpio/export");
+    if((fp = fopen(path, "w")) == NULL)
+	err(1, "%s", path);
+    fprintf(fp, "%i\n", rp); fflush(fp);
+    if(ferror(fp))
+	errx(1, "gpio%i: could not export", rp);
+    fclose(fp);
+    sprintf(path, "/sys/class/gpio/gpio%i", rp);
+    if(access(path, R_OK | X_OK))
+	errx(1, "gpio%i: still not available after export", rp);
+}
+
 static void setport(int p, int v)
 {
     char path[256], line[256];
     FILE *fp;
     int rv, rp;
     
-    if((rp = mappin(p)) < 0) {
-	fprintf(stderr, "gpio: %i: no such port\n", p);
-	exit(1);
-    }
+    if((rp = mappin(p)) < 0)
+	errx(1, "%i: no such port\n", p);
     sprintf(path, "/sys/class/gpio/gpio%i/direction", rp);
     if((fp = fopen(path, "r")) == NULL)
 	err(1, "%s", path);
     rv = !!fgets(line, sizeof(line), fp);
     fclose(fp);
     if(!rv || strcmp(line, "out\n")) {
+	if(preserve)
+	    errx(2, "gpio%i: not set to output", rp);
 	if((fp = fopen(path, "w")) == NULL)
 	    err(1, "%s", path);
 	fprintf(fp, "out\n"); fflush(fp);
@@ -59,7 +85,7 @@ static void setport(int p, int v)
 
 static void usage(FILE *out)
 {
-    fprintf(out, "usage: gpio [-hi] PORT=VAL...\n");
+    fprintf(out, "usage: gpio [-hip] PORT=VAL...\n");
 }
 
 int main(int argc, char **argv)
@@ -67,7 +93,7 @@ int main(int argc, char **argv)
     int c, i, port, val;
     char *p, *e;
     
-    while((c = getopt(argc, argv, "hi")) >= 0) {
+    while((c = getopt(argc, argv, "hip")) >= 0) {
 	switch(c) {
 	case 'h':
 	    usage(stdout);
@@ -76,6 +102,9 @@ int main(int argc, char **argv)
 	    umap = imap;
 	    mapn = sizeof(imap) / sizeof(*imap);
 	    break;
+	case 'p':
+	    preserve = 1;
+	    break;
 	default:
 	    usage(stderr);
 	    return(1);
@@ -100,6 +129,7 @@ int main(int argc, char **argv)
 	    fprintf(stderr, "gpio: %s: not of the form PORT=VAL\n", argv[i]);
 	    exit(1);
 	}
+	export(port);
 	setport(port, val);
     }
     return(0);
-- 
2.11.0