* Re: Tiny patch (w/ discussion) to provide the peer information on unix domain sockets
[not found] <20100330143512.GF7980@coffee.modeemi.cs.tut.fi>
@ 2010-03-30 14:56 ` Eric Dumazet
2010-03-30 17:39 ` Erkki Seppala
0 siblings, 1 reply; 2+ messages in thread
From: Eric Dumazet @ 2010-03-30 14:56 UTC (permalink / raw)
To: Erkki Seppala; +Cc: linux-kernel, netdev
Le mardi 30 mars 2010 à 17:35 +0300, Erkki Seppala a écrit :
> Hello,
>
> Attached you will find a patch that appends the field 'Peer' to
> /proc/net/unix indicating the peer of a connected unix domain
> socket. It shows its kernel address, as this is how unix domain
> sockets are identified in the same file. The preceding optional file
> name (actual address of the socket) field is replaced with "-" if it
> is not set. If there is no peer, 0 is used in its place.
>
> The purpose of the patch is to provide information on onto which
> services processes are connected. This information is readily
> available for TCP/IP sockets but not for unix domain sockets. The
> information can be retrieved with relative ease by using the following
> scripts for GDB, if you have GDB 7.1 and debugging symbols around:
>
> http://www.modeemi.fi/~flux/software/list-unix-sockets.tar.gz
>
> But obviously this is not optimal :). With the patch, this is how you
> can find out the peers of the sockets of the X server:
>
> # grep -E $(lsof -p `pidof X` | grep unix | awk '{print s $6; s="|"}' |
> tr -d '\n' | sed 's/0x//g;s/.*/(&)$/') /proc/net/unix
> d913b000: 00000003 00000000 00000000 0001 03 5494 - d913b200
> d9085600: 00000003 00000000 00000000 0001 03 5487 - d9085800
> ..
>
> The number in the first column is the address, for which the process
> can be most easily found with lsof:
>
> # lsof | grep d913b000
> gnome-pow 1245 gdm 3u unix 0xd913b000 0t0 5494 -
>
> Hopefully this kind of work would be integrated into lsof to display
> the information more easily.
>
> The patch does break the current API, but the impact seems rather
> light. I'm happy to incorporate alternative approaches if this seems
> to severe.
>
> Originally the last field in the field was fully optional: if it was
> not known, the line would terminate immediately after the field
> preceding it. Because we append a new field (instead of inserting it
> before Path, which causes more severe problems), the missing field
> value is indicated with a hyphen instead. So this (where $ indicates
> EOL):
>
> de38f800: 00000003 00000000 00000000 0001 03 2323$
>
> becomes this:
>
> de38f800: 00000003 00000000 00000000 0001 03 2323 - de2e4400$
>
> This changes the output of netstat -x for unix domain sockets that
> don't have a known address. I'm pretty sure nobody cares,
> though.. Similarly this changes the behavior of lsof, which before the
> patch can display:
>
> rxvt 17693 ese 6u unix 0xffff880050ba8900 0t0 746261 socket
>
> but after the patch:
>
> gconf-hel 1377 gdm 3u unix 0xd9197800 0t0 5796 -
>
> Pretty sure this is pretty much the same for everyone as well
> :). Although that could likely be worked around by using "@" in place
> of "-". Infact this might be the proper thing to do: I'm not sure what
> the meaning of UNIX_ABSTRACT used in af_unix.c:unix_seq_show is,
> perhaps just that there is no name to be found? I cannot use the
> macro, though, because it uses the nondefined field addr.
>
> Btw, I noticed that af_unix.c:unix_seq_show does not quote the unix
> domain socket path (possibly due to lacking convenient quoting
> function in seq_file.c), which allows spoofing the contents of the
> file into a certain extent. Atleast spaces should be quoted for this
> patch to work properly in the cases when socket names have spaces in
> them.
>
> Here is the patch, also available at
>
> http://www.modeemi.fi/~flux/software/linux-2.6.31-procfs-unix_peer_information.patch
>
> --- linux-2.6.31/net/unix/af_unix.c 2010-03-30 16:19:52.306372568 +0300
> +++ linux-2.6.31-flux/net/unix/af_unix.c 2010-03-30 14:32:47.000000000 +0300
> @@ -2154,7 +2154,7 @@
>
> if (v == SEQ_START_TOKEN)
> seq_puts(seq, "Num RefCount Protocol Flags Type St "
> - "Inode Path\n");
> + "Inode Path Peer\n");
> else {
> struct sock *s = v;
> struct unix_sock *u = unix_sk(s);
> @@ -2185,7 +2185,14 @@
> }
> for ( ; i < len; i++)
> seq_putc(seq, u->addr->name->sun_path[i]);
> - }
> + } else
> + seq_puts(seq, " -");
> +
> + if (u->peer)
> + seq_printf(seq, " %p", u->peer);
> + else
> + seq_puts(seq, " 0");
> +
> unix_state_unlock(s);
> seq_putc(seq, '\n');
> }
>
Hi Erkki
Such patches should be sent to netdev
I believe you missed some necessary locking.
Prior art from Kenan Kalajdzic :
http://patchwork.ozlabs.org/patch/46561/
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