On Mon, 26 Feb 2018 15:15:02 -0500 (EST)
David Miller [off-list ref] wrote:

From: Stephen Hemminger <stephen@networkplumber.org>
Date: Sat, 24 Feb 2018 11:04:52 -0800

quoted

This fixes an old bug in iproute2's ss command because it was
reading slabinfo to get statistics. There isn't a better API
to do this, and one can argue that /proc is a UAPI that must
not change.  

Please elaborate what kind of statistics are needed.

This is ancient original iproute2 code that dumpster dives into
slabinfo to get summary statistics on active objects.

	1) open sockets (sock_inode_cache)
	2) TCP ports bound (tcp_bind_buckets) [*]
	3) TCP time wait sockets (tw_sock_TCP) [*]
	4) TCP syn sockets (request_sock_TCP) [*]

From man page:

       -s, --summary
              Print summary statistics. This option does not parse socket lists  obtaining  summary  from
              various  sources. It is useful when amount of sockets is so huge that parsing /proc/net/tcp
              is painful.


The items with * are currently broken. See 0 for timewait, synrecv, and ports.

$ sudo ss -s

Total: 1089 (kernel 1093)
TCP:   33 (estab 4, closed 1, orphaned 0, synrecv 0, timewait 0/0), ports 0

Transport Total     IP        IPv6
*	  1093      -         -        
RAW	  0         0         0        
UDP	  21        13        8        
TCP	  32        24        8        
INET	  53        37        16       
FRAG	  0         0         0        

quoted

Therefore this patch set adds a flag to slab to give another
reason to prevent merging, and then uses it in network code.

The patches are against davem's linux-net tree and should also
goto stable as well.  

Well, as has been pointed out this never worked with SLUB so
in some sense this was always broken.

And the "UAPI" of slabinfo is to show the state of the various
slab caches.  And that's it.

If the implementation does merging or whatever, the UAPI is expressing
that and it's perfectly legitimate and not breaking UAPI in my
opinion.

I think the better solution is to grab the information from somewhere
else, so let's move this conversation along with the answer to my
question about asking for more details about what is needed by
iproute2.

Thank you.

There is no where else that gives summary information.

Both /proc/net/tcp and sock diag info require user space to
read all the data, which is what I think Alexey was trying to avoid.
Ideally there would be network namespace aware API to do this, but
the code (iproute2 and kernel) are currently broken. Some values
are missing (because they are merged) and some values have wrong
cache name (because of acme's changes to make this generic).


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