plugins: netlink: redesign to handle ENOBUFS with kernel resync

This is a major redesign of the netlink plugin to be able to handle
ENOBUFS¹ properly.  Pending verification, this change replaces the patch
to increase socket buffer size, which in real life turned out to be
insufficient.

When nl_callback() calls recv() and it fails with ENOBUFS, we consider
our cache of the kernel state invalid and thus:

  1. deassert all net/ conditions
  2. open a new (temporary) netlink socket
  3. send RTM_GETLINK  and re-assert all interfaces using nl_link()
  4. send RTM_GETROUTE and re-assert all routes with nl_route()

Like before, the kernel will not send us a RTM_DELROUTE when it removes
the default route, so we still have to track this ourselves.  This patch
also refactors that functionality to only resync routes when the ifindex
associated previosly with the default route goes down or is removed.

The previous change that added nl_default() to recheck, has been dropped
to instead reuse the standard nl_route() callback.
___
¹ see netlink(7) for details.

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

src/cond-w.c

@@ -178,13 +178,22 @@ void cond_update(const char *name)
 	}
 }
 
-void cond_set(const char *name)
+int cond_set_noupdate(const char *name)
 {
 	_d("%s", name);
 	if (string_compare(name, "nop"))
-		return;
+		return 1;
 
 	if (!cond_set_path(cond_path(name), COND_ON))
+		return 1;
+
+	return 0;
+}
+
+void cond_set(const char *name)
+{
+	_d("%s", name);
+	if (cond_set_noupdate(name))
 		return;
 
 	cond_update(name);
@@ -208,13 +217,22 @@ void cond_set_oneshot(const char *name)
 	cond_update(name);
 }
 
-void cond_clear(const char *name)
+int cond_clear_noupdate(const char *name)
 {
 	_d("%s", name);
 	if (string_compare(name, "nop"))
-		return;
+		return 1;
 
 	if (!cond_set_path(cond_path(name), COND_OFF))
+		return 1;
+
+	return 0;
+}
+
+void cond_clear(const char *name)
+{
+	_d("%s", name);
+	if (cond_clear_noupdate(name))
 		return;
 
 	cond_update(name);
@@ -227,7 +245,7 @@ void cond_reload(void)
 	cond_bump_reconf();
 }
 
-static int reassert(const char *fpath, const struct stat *sb, int tflg, struct FTW *ftw)
+static int do_assert(const char *fpath, const struct stat *sb, int tflg, struct FTW *ftw, int set)
 {
 	char *nm;
 
@@ -239,25 +257,47 @@ static int reassert(const char *fpath, const struct stat *sb, int tflg, struct F
 
 	nm = strstr((char *)fpath, COND_BASE);
 	if (!nm) {
-		_e("Incorrect condtion path %s, cannot reassert", fpath);
+		_e("Incorrect condtion path %s, cannot %sassert", fpath, set ? "re" : "de");
 		return 1;
 	}
 
 	nm += strlen(COND_BASE);
-	_d("Reasserting %s => %s", fpath, nm);
-	cond_set(nm);
+	_d("%sasserting %s => %s", set ? "Re" : "De", fpath, nm);
+	if (set)
+		cond_set(nm);
+	else
+		cond_clear_noupdate(nm); /* important, see netlink plugin! */
 
 	return 0;
 }
 
+static int reassert(const char *fpath, const struct stat *sb, int tflg, struct FTW *ftw)
+{
+	return do_assert(fpath, sb, tflg, ftw, 1);
+}
+
+static int deassert(const char *fpath, const struct stat *sb, int tflg, struct FTW *ftw)
+{
+	return do_assert(fpath, sb, tflg, ftw, 0);
+}
+
 /*
  * Used only by netlink plugin atm.
  * type: is a one of pid/, net/, etc.
  */
-void cond_reassert(const char *type)
+void cond_reassert(const char *pat)
 {
-	_d("%s", type);
-	nftw(cond_path(type), reassert, 20, FTW_DEPTH);
+	_d("%s", pat);
+	nftw(cond_path(pat), reassert, 20, FTW_DEPTH);
+}
+
+/*
+ * Used only by netlink plugin atm.
+ */
+void cond_deassert(const char *pat)
+{
+	_d("%s", pat);
+	nftw(cond_path(pat), deassert, 20, FTW_DEPTH);
 }
 
 void cond_init(void)

src/cond.h

@@ -34,7 +34,13 @@ void cond_set         (const char *name);
 void cond_set_oneshot (const char *name);
 void cond_clear       (const char *name);
 void cond_reload      (void);
+
+int cond_set_noupdate (const char *name);
+int cond_clear_noupdate(const char *name);
+
 void cond_reassert    (const char *pat);
+void cond_deassert    (const char *pat);
+
 void cond_init        (void);
 
 #endif	/* FINIT_COND_H_ */