net: fix /proc/net/ip_mr_cache display

/proc/net/ip6_mr_cache seems to display garbage when showing unresolved mfc6_cache entries.

$ cat /proc/net/ip6_mr_cache
Group        Origin    Iif    Pkts  Bytes     Wrong  Oifs
ff05::1     2003::1      1        4   4132        2  2:1    3:1  
ff05::3     2003::1  65535      514      2 -559067475
(addresses modified to increase  readability)

The first line is correct. It is a resolved cache entry, 4 packets used it, etc The second line represents an unresolved entry, and the columns Pkts(4th), Bytes(5th) and Wrong(6th) just show garbage.

In struct mfc6_cache, there's an union to store data for resolved and unresolved cases. And what ipmr_mfc_seq_show() is printing in these columns for the unresolved entries is some bytes from mfc6_cache.mfc_un.res. Bad.
(eg. In our case -559067475 is in fact 0xdead4ead which is the spinlock magic from mfc6_cache.mfc_un.unres.unresolved.lock.magic).

This patch only prints pkt, bytes and wrong_if when its relevant, ie. when showing a resolved cache entry.

Also, mfc->mfc_un.res.pkt, mfc->mfc_un.res.bytes, mfc->mfc_un.res.wrong_if are unsigned.

The patch also modifies IPv4 ipmr.c that contains similar code.

This patch applies on top of net-next-2.6.

The patch for net-2.6 is slightly different because of the NIP6_FMT to %pI6 conversion that was made in the seq_printf.

Regards,
Benjamin

---
 net/ipv4/ipmr.c  |   11 ++++++-----
 net/ipv6/ip6mr.c |   11 ++++++-----
 2 files changed, 12 insertions(+), 10 deletions(-)

Index: net-next-2.6/net/ipv4/ipmr.c
===================================================================
@@ -1879,15 +1879,16 @@ static int ipmr_mfc_seq_show(struct seq_
 		const struct mfc_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%08lX %08lX %-3d %8ld %8ld %8ld",
+		seq_printf(seq, "%08lX %08lX %-3d",
 			   (unsigned long) mfc->mfc_mcastgrp,
 			   (unsigned long) mfc->mfc_origin,
-			   mfc->mfc_parent,
-			   mfc->mfc_un.res.pkt,
-			   mfc->mfc_un.res.bytes,
-			   mfc->mfc_un.res.wrong_if);
+			   mfc->mfc_parent);
 
 		if (it->cache != &mfc_unres_queue) {
+			seq_printf(seq, " %8lu %8lu %8lu",
+				   mfc->mfc_un.res.pkt,
+				   mfc->mfc_un.res.bytes,
+				   mfc->mfc_un.res.wrong_if);
 			for (n = mfc->mfc_un.res.minvif;
 			     n < mfc->mfc_un.res.maxvif; n++ ) {
 				if (VIF_EXISTS(n)

Index: net-next-2.6/net/ipv6/ip6mr.c
===================================================================
@@ -297,14 +297,15 @@ static int ipmr_mfc_seq_show(struct seq_
 		const struct mfc6_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%pI6 %pI6 %-3d %8ld %8ld %8ld",
+		seq_printf(seq, "%pI6 %pI6 %-3d",
 			   &mfc->mf6c_mcastgrp, &mfc->mf6c_origin,
-			   mfc->mf6c_parent,
-			   mfc->mfc_un.res.pkt,
-			   mfc->mfc_un.res.bytes,
-			   mfc->mfc_un.res.wrong_if);
+			   mfc->mf6c_parent);
 
 		if (it->cache != &mfc_unres_queue) {
+			seq_printf(seq, " %8lu %8lu %8lu",
+				   mfc->mfc_un.res.pkt,
+				   mfc->mfc_un.res.bytes,
+				   mfc->mfc_un.res.wrong_if);
 			for (n = mfc->mfc_un.res.minvif;
 			     n < mfc->mfc_un.res.maxvif; n++) {
 				if (MIF_EXISTS(n) &&

Argh, my patch breaks iproute2 command: ip mroute show

iproute2 uses sscanf() to read /proc/net/ip_mr_cache and expects 6 fields to be read. For the unresolved entries my patch only displays the first three fields. As a consequence, 'ip mroute show' skips the unresolved entries. :(

So we can
- either forget this patch and keep displaying garbage information in /proc/net/ip[6]_mr_cache for the unresolved entries. (No one complained before)
- or may be we can just print '-' or 0 for the fields that have no data associated in the unresolved case.

Tell me what you prefer.

Benjamin

B e n j a m i n   T h e r y  - BULL/DT/Open Software R&D

   http://www.bull.com

/proc file formats are part of the Linux ABI and can't change!

Stephen Hemminger <[email protected]> a écrit :

Yes, of course I know that. But as in this case part of the data displayed in /proc/net/ip_mr_cache and /proc/net/ip6_mr_cache for unresolved cache entries are complete rubbish (see the patch description), I thought it can be improved.

The right way to fix it, IMHO, is to print 0 (zero) in the columns that have no meaning for the unresolved entries. That way we don't break the ABI: the userspace expects to get at least 6 numbers for each entries, it gets 6 numbers. It's easy to figure what zeros represent and this prevent people from wasting time trying to figure what to do with these "random" numbers on the unresolved entries, no?

Regards,
Benjamin

----------------------------------------------------------------
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From: "Benjamin Thery " <[email protected]>
Date: Mon, 01 Dec 2008 21:17:02 +0100

Probably, this is correct.

However, we could run into problems if userland parsers expect 6 entries and then expect an immediate newline. We'd break that.

The only thing that really works for extending files like this is if they are already exporting a "key: value" interface, then you can add new lines safely.

Doing this horizontal expansion as you are proposing here is, on the other hand, very risky and dangerous.

I really don't think it's worth it.

Fix the garbage values, or flush them to zero if we can't represent them properly. But don't add new stuff horizontally to "fill in the gaps", as I don't think it can be done %100 safely.

I won't do any horizontal expansion.
Maybe my explanations where not very clear (due to my bad english I guess). Let's try to reformulate :)

Today, /proc/net/ip_mr_cache output looks like this:

[root@qemu tests]# cat /proc/net/ip_mr_cache
Group Origin Iif Pkts Bytes Wrong Oifs
014C00EF 010014AC 1 10 10050 0 2:1 3:1
024C00EF 010014AC 65535 514 2 -559067475

It displays resolved and unresolved mfc_caches.
Both type of entries have at least 6 fields printed (resolved have more).
1st line is a resolved cache entry.
2nd line is an unresolved cache entry.

In the case of unresolved entries, columns Pkts, Bytes and Wrong displays garbage data (due to the union in struct mfc_cache).

My first patch was completely wrong as it suppressed these fields for the unresolved lines, but my proposal now is _only_ to replace the garbage values with zeros. Like this:

[root@qemu tests]# cat /proc/net/ip_mr_cache
Group Origin Iif Pkts Bytes Wrong Oifs

014C00EF 010014AC 1          8     8040        0  2:1    3:1
024C00EF 010014AC 65535      0        0        0

It shouldn't break the ABI.
I will send an updated patch for this.

Also, there is another bug.
Today, iproute2 already fails to show unresolved entries because it expects to see -1 in 'Iif' column to identify unresolved entries but the kernel output 65535. It's a signed/unsigned issue:

'Iif', the source interface, is retrieved from member mfc_parent in struct mfc_cache. mfc_parent is a vifi_t: unsigned short, but is displayed in ipmr_mfc_seq_show() as "%-3d", signed integer.

In unresolevd entries, the 65535 value (0xFFFF) comes from this define:
#define ALL_VIFS ((vifi_t)(-1))

That may explains why the guy who added support for this in iproute2 thought a -1 should be expected.

I don't know if this must be fixed in kernel or in iproute2. Who is right?

I will send another patch for this one, which fix 'Iif' display and let you or Stephen decide if it should be merged in kernel or fixed in iproute2.

Regards,
Benjamin

B e n j a m i n   T h e r y  - BULL/DT/Open Software R&D

   http://www.bull.com

/proc/net/ip_mr_cache and /proc/net/ip6_mr_cache displays garbage when showing unresolved mfc_cache entries.

[root@qemu tests]# cat /proc/net/ip_mr_cache
Group Origin Iif Pkts Bytes Wrong Oifs
014C00EF 010014AC 1 10 10050 0 2:1 3:1
024C00EF 010014AC 65535 514 2 -559067475

The first line is correct. It is a resolved cache entry, 10 packets used it... The second line represents an unresolved entry, and the columns Pkts(4th), Bytes(5th) and Wrong(6th) just show garbage.

In struct mfc_cache, there's an union to store data for resolved and unresolved cases. And what ipmr_mfc_seq_show() is printing in these columns for the unresolved entries is some bytes from mfc_cache.mfc_un.res. Bad.
(eg. In our case -559067475 is in fact 0xdead4ead which is the spinlock magic from mfc_cache.mfc_un.unres.unresolved.lock.magic).

This patch replaces the garbage data written in these columns for the unresolved entries by '0' (zeros) which is more correct. This change doesn't break the ABI.

Also, mfc->mfc_un.res.pkt, mfc->mfc_un.res.bytes, mfc->mfc_un.res.wrong_if are unsigned long.

It applies on top of net-next-2.6.

The patch for net-2.6 is slightly different because of the NIP6_FMT to %pI6 conversion that was made in the seq_printf.

Changelog:
==========
V2:
* Instead of breaking the ABI by suppressing the columns that have no meaning for unresolved entries, fill them with 0 values.

---
 net/ipv4/ipmr.c  |   16 +++++++++++-----
 net/ipv6/ip6mr.c |   16 +++++++++++-----
 2 files changed, 22 insertions(+), 10 deletions(-)

index 77fc4d3..cb3a57d 100644
@@ -1879,15 +1879,16 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 		const struct mfc_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%08lX %08lX %-3d %8ld %8ld %8ld",
+		seq_printf(seq, "%08lX %08lX %-3d",
 			   (unsigned long) mfc->mfc_mcastgrp,
 			   (unsigned long) mfc->mfc_origin,
-			   mfc->mfc_parent,
-			   mfc->mfc_un.res.pkt,
-			   mfc->mfc_un.res.bytes,
-			   mfc->mfc_un.res.wrong_if);
+			   mfc->mfc_parent);
 
 		if (it->cache != &mfc_unres_queue) {
+			seq_printf(seq, " %8lu %8lu %8lu",
+				   mfc->mfc_un.res.pkt,
+				   mfc->mfc_un.res.bytes,
+				   mfc->mfc_un.res.wrong_if);
 			for (n = mfc->mfc_un.res.minvif;
 			     n < mfc->mfc_un.res.maxvif; n++ ) {
 				if (VIF_EXISTS(n)

@@ -1896,6 +1897,11 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 					   " %2d:%-3d",
 					   n, mfc->mfc_un.res.ttls[n]);
 			}
+		} else {
+			/* unresolved mfc_caches don't contain
+			 * pkt, bytes and wrong_if values
+			 */
+			seq_printf(seq, " %8lu %8lu %8lu", 0ul, 0ul, 0ul);
 		}
 		seq_putc(seq, '\n');
 	}

index dfba9fd..2dc4b01 100644
@@ -297,14 +297,15 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 		const struct mfc6_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%pI6 %pI6 %-3d %8ld %8ld %8ld",
+		seq_printf(seq, "%pI6 %pI6 %-3d",
 			   &mfc->mf6c_mcastgrp, &mfc->mf6c_origin,
-			   mfc->mf6c_parent,
-			   mfc->mfc_un.res.pkt,
-			   mfc->mfc_un.res.bytes,
-			   mfc->mfc_un.res.wrong_if);
+			   mfc->mf6c_parent);
 
 		if (it->cache != &mfc_unres_queue) {
+			seq_printf(seq, " %8lu %8lu %8lu",
+				   mfc->mfc_un.res.pkt,
+				   mfc->mfc_un.res.bytes,
+				   mfc->mfc_un.res.wrong_if);
 			for (n = mfc->mfc_un.res.minvif;
 			     n < mfc->mfc_un.res.maxvif; n++) {
 				if (MIF_EXISTS(n) &&

@@ -313,6 +314,11 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 						   " %2d:%-3d",
 						   n, mfc->mfc_un.res.ttls[n]);
 			}
+		} else {
+			/* unresolved mfc_caches don't contain
+			 * pkt, bytes and wrong_if values
+			 */
+			seq_printf(seq, " %8lu %8lu %8lu", 0ul, 0ul, 0ul);
 		}
 		seq_putc(seq, '\n');
 	}

From: Benjamin Thery <[email protected]>
Date: Wed, 03 Dec 2008 15:35:41 +0100

Applied to net-next-2.6

Today, iproute2 fails to show multicast forwarding unresolved cache entries while scanning /proc/net/ip_mr_cache.

Indeed, it expects to see -1 in 'Iif' column to identify unresolved entries but the kernel outputs 65535. It's a signed/unsigned issue:

'Iif', the source interface, is retrieved from member mfc_parent in struct mfc_cache. mfc_parent is a vifi_t: unsigned short, but is displayed in ipmr_mfc_seq_show() as "%-3d", signed integer.

In unresolevd entries, the 65535 value (0xFFFF) comes from this define:
#define ALL_VIFS ((vifi_t)(-1))

That may explains why the guy who added support for this in iproute2 thought a -1 should be expected.

I don't know if this must be fixed in kernel or in iproute2. Who is right? What is the correct API? How was it designed originally?

I let you decide if it should goes in the kernel or be fixed in iproute2.

---
 net/ipv4/ipmr.c  |    2 +-
 net/ipv6/ip6mr.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

index cb3a57d..244a624 100644
@@ -1879,7 +1879,7 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 		const struct mfc_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%08lX %08lX %-3d",
+		seq_printf(seq, "%08lX %08lX %-3hd",
 			   (unsigned long) mfc->mfc_mcastgrp,
 			   (unsigned long) mfc->mfc_origin,
 			   mfc->mfc_parent);

index 2dc4b01..1446bec 100644
@@ -297,7 +297,7 @@ static int ipmr_mfc_seq_show(struct seq_file *seq, void *v)
 		const struct mfc6_cache *mfc = v;
 		const struct ipmr_mfc_iter *it = seq->private;
 
-		seq_printf(seq, "%pI6 %pI6 %-3d",
+		seq_printf(seq, "%pI6 %pI6 %-3hd",
 			   &mfc->mf6c_mcastgrp, &mfc->mf6c_origin,
 			   mfc->mf6c_parent);
 

From: Benjamin Thery <[email protected]>
Date: Wed, 03 Dec 2008 15:35:42 +0100

For now I think the kernel is the best place to handle this, thus applied to net-next-2.6

Thanks!