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

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Message-ID: <87k3wzalux.fsf@xmission.com>
Date:	Wed, 15 Aug 2012 14:25:42 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	tglx@...utronix.de, mingo@...hat.com, davem@...emloft.net,
	thierry.reding@...onic-design.de, bfields@...hat.com,
	eric.dumazet@...il.com, xemul@...allels.com, neilb@...e.de,
	netdev@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, paul.gortmaker@...driver.com,
	viro@...iv.linux.org.uk, gorcunov@...nvz.org,
	akpm@...ux-foundation.org, tim.c.chen@...ux.intel.com,
	devel@...nvz.org
Subject: Re: [RFC PATCH 0/5] net: socket bind to file descriptor introduced

"H. Peter Anvin" <hpa@...or.com> writes:

> On 08/15/2012 12:49 PM, Eric W. Biederman wrote:
>> 
>> There is also the trick of getting a shorter directory name using
>> /proc/self/fd if you are threaded and can't change the directory.
>> 
>> The obvious choices at this point are
>> - Teach bind and connect and af_unix sockets to take longer AF_UNIX
>>   socket path names.
>> 
>> - introduce sockaddr_fd that can be applied to AF_UNIX sockets,
>>   and teach unix_bind and unix_connect how to deal with a second type of sockaddr.
>>   struct sockaddr_fd { short fd_family; short pad; int fd; };
>> 
>> - introduce sockaddr_unix_at that takes a directory file descriptor
>>   as well as a unix path, and teach unix_bind and unix_connect to deal with a
>>   second sockaddr type.
>>   struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
>>   AF_UNIX_AT
>> 
>> I don't know what the implications of for breaking connect up into 3
>> system calls and changing the semantics are and I would really rather
>> not have to think about it.
>> 
>> But it certainly does not look to me like you introduce new systems
>> calls to do what you want.
>> 
>
> How would you distinguish the new sockaddr types from the traditional
> one?  New AF_?

Yeah.  AF_FD or AF_UNIX_AT is what I was thinking.  The way the code
falls out that should be compartively simple to implement.

recvmsg etc would give you sockaddr_un sockets when they come from the
kernel.

Eric
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