ifctrstat: Add ability to output counter values

cmd/ifctrstat-linux.c

@@ -14,7 +14,9 @@
  */
 
 #include <errno.h>
+#include <limits.h>
 #include <stdio.h>
+#include <string.h>
 #include "multicall.h"
 
 const char *avail_counters[] = {
@@ -30,9 +32,69 @@ const char *avail_counters[] = {
 
 size_t avail_counters_count = ARRAY_SIZE(avail_counters);
 
-const char *
+char *
 read_counter(const char *interface, const char *counter)
 {
-	errno = ENOSYS;
-	return NULL;
+	FILE *fp;
+	const char *path;
+	char full_path[PATH_MAX];
+	char buffer[1024];
+	size_t in_count;
+
+	errno = 0;
+
+	if (strcasecmp(counter, "rx.octets") == 0)
+	{
+		path = "rx_bytes";
+	} else if (strcasecmp(counter, "rx.packets") == 0) {
+		path = "rx_packets";
+	} else if (strcasecmp(counter, "rx.discard") == 0) {
+		path = "rx_dropped";
+	} else if (strcasecmp(counter, "rx.errors") == 0) {
+		path = "rx_errors";
+	} else if (strcasecmp(counter, "tx.octets") == 0) {
+		path = "tx_bytes";
+	} else if (strcasecmp(counter, "tx.packets") == 0) {
+		path = "tx_packets";
+	} else if (strcasecmp(counter, "tx.discard") == 0) {
+		path = "tx_dropped";
+	} else if (strcasecmp(counter, "tx.errors") == 0) {
+		path = "tx_errors";
+	} else {
+		errno = ENOSYS;
+		return NULL;
+	}
+
+	if (snprintf(full_path, PATH_MAX, "/sys/class/net/%s/statistics/%s", interface, path) > PATH_MAX)
+	{
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	fp = fopen(full_path, "r");
+	if (!fp)
+	{
+		return NULL;
+	}
+
+	in_count = fread(buffer, 1, sizeof(buffer), fp);
+
+	if (in_count == sizeof(buffer))
+	{
+		errno = ENOMEM;
+		fclose(fp);
+		return NULL;
+	}
+
+	if (ferror(fp))
+	{
+		return NULL;
+	}
+
+	fclose(fp);
+
+	/* take away the \n, we add our own */
+	buffer[in_count - 1] = '\0';
+
+	return strdup(buffer);
 }