netdev - Re: Polling on sockets in kernel space and struct file

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Date:	Wed, 08 Dec 2010 16:02:53 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Martin Sustrik <sustrik@...bpm.com>
Cc:	netdev@...r.kernel.org, Martin Lucina <mato@...elna.sk>
Subject: Re: Polling on sockets in kernel space and struct file

Le mercredi 08 décembre 2010 à 15:33 +0100, Martin Sustrik a écrit :
> Hi all,
> 
> As part of implementing a new experimental protocol family, we are 
> trying to create a socket in kernel. This seems to be easy, just use 
> sock_create_kern(). However, the socket returned by this function does 
> not have associated file structure; thus it cannot be polled on using 
> poll_initwait() and friends.
> 
> We have tried to create the appropriate struct file using sock_map_fd(), 
> but this has two problems:
> 
> 1) We do not want our internal socket to be visible in the process 
> context, i.e. it should not have a file descriptor.



> 
> 2) During process exit, we get a kernel BUG from iput() in fs/inode.c:1260.
> 

you could call sock_map_fd() then :


	int fd = sock_map_fd(sock, flags);
	struct file *file = NULL;

	if (fd != -1) {
		file = fget(fd);
		sys_close(fd);  /* still racy */
	}

	if (file) ...

Take a look at net/9p/trans_fd.c

> We then tried another approach using anon_inode_getfile() to get a 
> struct file, but this still produces the problem 2) above.
> 
> Any help/advice on how to proceed would be appreciated; for reference 
> our work in progress can be seen at
> 
> http://github.com/sustrik/linux-2.6/blob/sp-v2.6.36/net/sp/af_sp.c


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