[CRIU] alternate implementation of --ext-unix-sk

[Pavel Emelyanov]

On 11/10/2015 03:00 AM, Tycho Andersen wrote:
> Hi all,
> 
> in 79fd764ae6c4eabcc12da0159e4ad96b02431df0 and
> http://criu.org/External_UNIX_socket#What_to_do_with_socketpair.28.29-s.3F
> 
> an implementation of --ext-unix-sk is described that you pass the
> inode of the external socket. One way to find this inode is to look
> for a specific path in /proc/net/unix inside the container's netns.
> 
> Is there any reason we can't just pass --ext-unix-sk=/foo/bar and have
> every socket connected to this be dumpable and restorable (by being
> reconnected as described on the wiki)? This would be less work (and
> more intiutive, I think) for most than passing the inode number, but I
> might be missing something.

The path is quite bad socket identifier because different sockets may have
the same name.

Another argument for the inode number was -- at restore time caller will
have to create a socket pair and pass one end of it into the criu via the
--inherit-fd option. In other words user of external unix sockets feature
deals with sockets via file descriptor on restore and thus, likely, on
dump too. But getting inode number out of descriptor is slightly easier 
than getting the socket path via it -- stat() returns 4 bytes number, while
getsockname() returns a string, that can start with \0 (anonymous socket
names), then you have to call strlen(), allocate memory for option and and
copy name there.

-- Pavel