echo(): refactor and rename helper function -> fnwrite()

More often than not, the file to write to in sysfs changes rather than
the value.  This patch changes echo() into a fnwrite(), flipping what
is vsnprintf()'ed, and adds a stupid str() function that converts any
value (float/int/double/uint64_t) to a static string buffer.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/cgroup.c

@@ -41,24 +41,18 @@ static uev_t cgw;
 
 static void group_init(char *path, int leaf, int weight)
 {
-	char file[strlen(path) + 64];
-
 	if (mkdir(path, 0755) && EEXIST != errno) {
 		_pe("Failed creating cgroup %s", path);
 		return;
 	}
 
 	/* enable detected controllers on domain groups */
-	if (!leaf) {
-		paste(file, sizeof(file), path, "cgroup.subtree_control");
-		echo(file, 0, controllers);
-	}
+	if (!leaf)
+		fnwrite(controllers, "%s/cgroup.subtree_control", path);
 
 	/* set initial group weight */
-	if (weight) {
-		paste(file, sizeof(file), path, "cpu.weight");
-		echo(file, 0, "%d", weight);
-	}
+	if (weight)
+		fnwrite(str("%d", weight), "%s/cgroup.subtree_control", path);
 }
 
 static int cgroup_leaf_init(char *group, char *name, int pid)
@@ -70,13 +64,14 @@ static int cgroup_leaf_init(char *group, char *name, int pid)
 		return 1;
 	}
 
+	/* create and initialize new group */
 	snprintf(path, sizeof(path), "/sys/fs/cgroup/%s/%s", group, name);
 	group_init(path, 1, 0);
 
-	strlcat(path, "/cgroup.procs", sizeof(path));
-	echo(path, 0, "%d", pid);
+	/* move process to new group */
+	fnwrite(str("%d", pid), "%s/cgroup.procs", path);
 
-	snprintf(path, sizeof(path), "/sys/fs/cgroup/%s/%s/cgroup.events", group, name);
+	strlcat(path, "/cgroup.events", sizeof(path));
 
 	return iwatch_add(&iw_cgroup, path, 0);
 }
@@ -207,7 +202,7 @@ void cgroup_init(uev_ctx_t *ctx)
 	fclose(fp);
 
 	/* Enable all controllers */
-	echo(FINIT_CGPATH "/cgroup.subtree_control", 0, controllers);
+	fnwrite(controllers, FINIT_CGPATH "/cgroup.subtree_control");
 
 	/* Default groups, PID 1, services, and user/login processes */
 	group_init(FINIT_CGPATH "/init",   1,  100);
@@ -215,7 +210,7 @@ void cgroup_init(uev_ctx_t *ctx)
 	group_init(FINIT_CGPATH "/system", 0, 9800);
 
 	/* Move ourselves to init */
-	echo(FINIT_CGPATH "/init/cgroup.procs", 0, "1");
+	fnwrite("1", FINIT_CGPATH "/init/cgroup.procs");
 
 	/* prepare cgroup.events watcher */
 	fd = iwatch_init(&iw_cgroup);

src/util.c

@@ -56,28 +56,41 @@ char *progname(char *arg0)
        return prognm;
 }
 
-int echo(char *file, int append, char *fmt, ...)
+char *str(char *fmt, ...)
 {
+	static char buf[32];
+	va_list ap;
+
+	va_start(ap, fmt);
+	vsnprintf(buf, sizeof(buf), fmt, ap);
+	va_end(ap);
+
+	return buf;
+}
+
+int fnwrite(char *value, char *fmt, ...)
+{
+	char path[256];
 	va_list ap;
 	FILE *fp;
 
-	if (!file)
-		fp = stdout;
-	else
-		fp = fopen(file, append ? "a" : "w");
+	if (!value) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	va_start(ap, fmt);
+	vsnprintf(path, sizeof(path), fmt, ap);
+	va_end(ap);
+
+	fp = fopen(path, "w");
 	if (!fp)
 		return -1;
 
-	if (fmt) {
-		va_start(ap, fmt);
-		vfprintf(fp, fmt, ap);
-		va_end(ap);
-	}
-
 	/* echo(1) always adds a newline */
-	fprintf(fp, "\n");
-	if (file)
-		fclose(fp);
+	fputs(value, fp);
+	fputs("\n", fp);
+	fclose(fp);
 
 	return 0;
 }

src/util.h

@@ -45,7 +45,10 @@ extern char *prognm;
 #include <lite/conio.h>
 
 char *progname     (char *arg0);
-int   echo         (char *file, int append, char *fmt, ...);
+
+char *str          (char *fmt, ...);
+int   fnwrite      (char *value, char *fmt, ...);
+
 int   has_utmp     (void);
 int   strtobytes   (char *arg);
 void  do_sleep     (unsigned int sec);