Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

[Stanislav Kinsbursky]

06.10.2012 00:00, J. Bruce Fields ÐÐÑÐÑ:
> On Tue, Sep 04, 2012 at 03:00:07PM -0400, bfields wrote:
> > On Mon, Aug 20, 2012 at 02:18:13PM +0400, Stanislav Kinsbursky wrote:
> > > 16.08.2012 07:03, Eric W. Biederman ÐÐÑÐÑ:
> > > > Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx> writes:
> > > >
> > > > > This patch set introduces new socket operation and new system call:
> > > > > sys_fbind(), which allows to bind socket to opened file.
> > > > > File to bind to can be created by sys_mknod(S_IFSOCK) and opened by
> > > > > open(O_PATH).
> > > > >
> > > > > This system call is especially required for UNIX sockets, which has name
> > > > > lenght limitation.
> > > > >
> > > > > The following series implements...
> > > >
> > > > Hmm.  I just realized this patchset is even sillier than I thought.
> > > >
> > > > Stanislav is the problem you are ultimately trying to solve nfs clients
> > > > in a container connecting to the wrong user space rpciod?
> > >
> > > Hi, Eric.
> > > The problem you mentioned was the reason why I started to think about this.
> > > But currently I believe, that limitations in unix sockets connect or
> > > bind should be removed, because it will be useful it least for CRIU
> > > project.
> > >
> > > > Aka net/sunrpc/xprtsock.c:xs_setup_local only taking an absolute path
> > > > and then creating a delayed work item to actually open the unix domain
> > > > socket?
> > > >
> > > > The straight correct and straight forward thing to do appears to be:
> > > > - Capture the root from current->fs in xs_setup_local.
> > > > - In xs_local_finish_connect change current->fs.root to the captured
> > > >    version of root before kernel_connect, and restore current->fs.root
> > > >    after kernel_connect.
> > > >
> > > > It might not be a bad idea to implement open on unix domain sockets in
> > > > a filesystem as create(AF_LOCAL)+connect() which would allow you to
> > > > replace __sock_create + kernel_connect with a simple file_open_root.
> > >
> > > I like the idea of introducing new family (AF_LOCAL_AT for example)
> > > and new sockaddr for connecting or binding from specified root. The
> > > only thing I'm worrying is passing file descriptor to unix bind or
> > > connect routine. Because this approach doesn't provide easy way to
> > > use such family and sockaddr in kernel (like in NFS example).
> > >
> > > > But I think the simple scheme of:
> > > > struct path old_root;
> > > > old_root = current->fs.root;
> > > > kernel_connect(...);
> > > > current->fs.root = old_root;
> > > >
> > > > Is more than sufficient and will remove the need for anything
> > > > except a purely local change to get nfs clients to connect from
> > > > containers.
> > >
> > > That was my first idea.
> >
> > So is this what you're planning on doing now?
>
> What ever happened to this?

Sorry, was busy.
I'll prepare patch today, I hope.

> --b.
>
> > > And probably it would be worth to change all
> > > fs_struct to support sockets with relative path.
> > > What do you think about it?
> >
> > I didn't understand the question.  Are you suggesting that changes to
> > fs_struct would be required to make this work?  I don't see why.
> >
> > --b.


--
Best regards,
Stanislav Kinsbursky
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