Sockets

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Revision as of 19:09, 21 October 2012 by Xemul (talk | contribs) (What should be done next)
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Unix sockets initial support

Currently it can only work with stream and dgram sockets, which have no skbs in queues (listening or established -- both work OK). If there are skbs in queue the dumping procedure will fail.

The cpt part uses the sock_diag engine that was merged to Dave recently to collect sockets. Then it dumps sockets by checking the filesystem ID of a failed-to-open through /proc/pid/fd descriptors (sockets do not allow for such tricks with opens through proc) against SOCKFS_TYPE.

The restore part is more tricky. Listen sockets are just restored, this is simple. Connected sockets are restored like this:

  1. One end establishes a listening anon socket at the desired descriptor;
  2. The other end just creates a socket at the desired descriptor;
  3. All sockets, that are to be connect()-ed call connect. Unix sockets do not block connect() till the accept() time and thus we continue with...
  4. ... all listening sockets call accept() and ... dup2 the new fd into the accepting end.

There's a problem with this approach -- socket names are not preserved, but looking into our OpenVZ implementation I think this is OK for existing apps.

What should be done next

  • socket filter (SK_ATTACH_FILTER)
  • various (ip/tcp level) sockoptions