[iproute2][PATCH] tc: mirred target: do not report non-existing devices

[Dan Kenigsberg <danken@redhat.com>]

Currently, if a mirred target device is removed, `tc filter show`
does not reveal the fact. Instead, it replaces the original name of the
device with the default output of ll_map:ll_idx_n2a().

This is unfortunate, since one cannot differ between this case and a valid
mirroring target device named 'if17'.

It seems that the original code meant to report an error message in this
case, but it does not, since ll_index_to_name() never returns 0. I would
not like to bail out in case of an error, since the user would still be
interested to know what are the other details of the action.

Signed-off-by: Dan Kenigsberg <danken@redhat.com>
---
 lib/ll_map.c  |   13 +++++++++++++
 tc/m_mirred.c |   10 ++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/lib/ll_map.c b/lib/ll_map.c
index 1ca781e..8ceef41 100644
--- a/lib/ll_map.c
+++ b/lib/ll_map.c
@@ -108,6 +108,19 @@ const char *ll_idx_n2a(unsigned idx, char *buf)
 	return buf;
 }
 
+char *ll_index_exists(unsigned idx)
+{
+	const struct ll_cache *im;
+
+	if (idx == 0)
+		return 0;
+
+	for (im = idxhead(idx); im; im = im->idx_next)
+		if (im->index == idx)
+			return 1;
+
+	return 0;
+}
 
 const char *ll_index_to_name(unsigned idx)
 {
diff --git a/tc/m_mirred.c b/tc/m_mirred.c
index 0d771bc..eba1240 100644
--- a/tc/m_mirred.c
+++ b/tc/m_mirred.c
@@ -268,13 +268,11 @@ print_mirred(struct action_util *au,FILE * f, struct rtattr *arg)
 	ll_init_map(&rth);
 	*/
 
+	dev = ll_index_to_name(p->ifindex);
 
-	if ((dev = ll_index_to_name(p->ifindex)) == 0) {
-		fprintf(stderr, "Cannot find device %d\n", p->ifindex);
-		return -1;
-	}
-
-	fprintf(f, "mirred (%s to device %s) %s", mirred_n2a(p->eaction), dev,action_n2a(p->action, b1, sizeof (b1)));
+	fprintf(f, "mirred (%s to %sdevice %s) %s", mirred_n2a(p->eaction),
+                ll_index_exists(p->ifindex) ? "" : "missing-",
+                dev, action_n2a(p->action, b1, sizeof (b1)));
 
 	fprintf(f, "\n ");
 	fprintf(f, "\tindex %d ref %d bind %d",p->index,p->refcnt,p->bindcnt);
-- 
1.7.7.6