Subject: Re: [PATCH net-next 1/2] socket: Allow external sockets to use socket syscalls

From: Alex Gartrell <[email-masked]>
Date: Fri, 26 Dec 2014 14:26:24 -0500

Hello Jason,

Thanks again for your comments.

On 12/26/14 4:45 AM, Jason Wang wrote:
>> @@ -388,6 +388,7 @@ struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname)
>>   	sock->file = file;
>>   	file->f_flags = O_RDWR | (flags & O_NONBLOCK);
>>   	file->private_data = sock;
>> +	file->private_data_is_socket = true;
>
> This is only safe if all user of sock_alloc_file() have full support for
> each method in proto_ops.

This doesn't change anything in the invocation of the syscalls, as every 
file allocated through this path already passes the "is_socket" test due 
to the (sadly missing here)
     file = alloc_file(..., &socket_file_ops)
above, so this makes things no less safe than they were.

Of course we also need to implement these proto_ops for the tun device 
in the subsequent patch to make it work.

>>   	return file;
>>   }
>>   EXPORT_SYMBOL(sock_alloc_file);
>> @@ -411,7 +412,7 @@ static int sock_map_fd(struct socket *sock, int flags)
>>
>>   struct socket *sock_from_file(struct file *file, int *err)
>>   {
>> -	if (file->f_op == &socket_file_ops)
>> +	if (file->private_data_is_socket)
>>   		return file->private_data;	/* set in sock_map_fd */
>>
>>   	*err = -ENOTSOCK;
>
> Not sure it's the best method, how about a dedicated f_op to do this?

So like a get_socket operation?  That would simplify this a lot, 
certainly (we wouldn't need to move private_data around in the tun driver).

Thanks,
-- 
Alex Gartrell <[email-masked]>