[PATCH iproute2-next 1/4] utils: Introduce do_each_proc_net_dev() helper

[Serhey Popovych <serhe.popovych@gmail.com>]

It is natural for ip(8) tool to access /proc/net/dev for various
information and there at least two places implementing same iteration
over lines in this file: iptunnel.c and ip6tunnel.c.

To unify interface and avoid code duplication introduce helper that
reads line from /proc/net/dev, passes it to given callback function
that may return following three states to control do_each_proc_net_dev()
behaviour:

  o PND_ERROR - stop reading lines and return -1
  o PND_OK    - stop reading lines and return 0
  o PND_NEXT  - continue by reading next line.

Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
---
 include/utils.h |   10 ++++++++++
 lib/utils.c     |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/include/utils.h b/include/utils.h
index 0394268..819b0ca 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -285,6 +285,16 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
 int do_each_netns(int (*func)(char *nsname, void *arg), void *arg,
 		bool show_label);
 
+typedef enum {
+	PND_ERROR = -1,
+	PND_OK    = 0,
+	PND_NEXT  = 1
+} pnd_result_t;
+
+typedef pnd_result_t (pnd_func_t)(char *name, char *stats, void *arg);
+
+int do_each_proc_net_dev(pnd_func_t f, void *arg);
+
 char *int_to_str(int val, char *buf);
 int get_guid(__u64 *guid, const char *arg);
 int get_real_family(int rtm_type, int rtm_family);
diff --git a/lib/utils.c b/lib/utils.c
index 8e15625..4f142d8 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -1375,6 +1375,57 @@ int do_each_netns(int (*func)(char *nsname, void *arg), void *arg,
 	return netns_foreach(on_netns, &nsf);
 }
 
+int do_each_proc_net_dev(pnd_func_t f, void *arg)
+{
+	static const char pnd[] = "/proc/net/dev";
+	char buf[512];
+	int err = -1;
+	FILE *fp;
+
+	fp = fopen(pnd, "r");
+	if (!fp) {
+		perror("fopen");
+		return -1;
+	}
+
+	/* skip two lines at the begenning of the file */
+	if (!fgets(buf, sizeof(buf), fp) ||
+	    !fgets(buf, sizeof(buf), fp)) {
+		perror("fgets");
+		goto end;
+	}
+
+	while (fgets(buf, sizeof(buf), fp)) {
+		char *stats, *name = NULL;
+		pnd_result_t result;
+
+		buf[sizeof(buf) - 1] = '\0';
+		stats = strchr(buf, ':');
+		if (stats) {
+			*stats++ = '\0';
+			if (!check_ifname(buf))
+				name = buf;
+		}
+		if (!name) {
+			fprintf(stderr,
+				"Wrong format for \"%s\". Giving up.\n", pnd);
+			goto end;
+		}
+
+		result = f(name, stats, arg);
+		if (result == PND_NEXT)
+			continue;
+		if (result == PND_OK)
+			break;
+		goto end;
+	}
+	if (feof(fp))
+		err = 0;
+end:
+	fclose(fp);
+	return err;
+}
+
 char *int_to_str(int val, char *buf)
 {
 	sprintf(buf, "%d", val);
-- 
1.7.10.4