linux-kernel - Re: [PATCH 0/7] [RFC] kernel: add a netlink interface to get information about processes

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Date:	Wed, 18 Feb 2015 15:42:11 +0300
From:	Andrew Vagin <avagin@...allels.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Andrey Vagin <avagin@...nvz.org>, <linux-kernel@...r.kernel.org>,
	<linux-api@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Pavel Emelyanov" <xemul@...allels.com>,
	Roger Luethi <rl@...lgate.ch>
Subject: Re: [PATCH 0/7] [RFC] kernel: add a netlink interface to get
 information about processes

On Wed, Feb 18, 2015 at 12:06:40PM +0100, Arnd Bergmann wrote:
> On Wednesday 18 February 2015 00:33:13 Andrew Vagin wrote:
> > On Tue, Feb 17, 2015 at 09:53:09AM +0100, Arnd Bergmann wrote:
> > > On Tuesday 17 February 2015 11:20:19 Andrey Vagin wrote:
> > > > task_diag is based on netlink sockets and looks like socket-diag, which
> > > > is used to get information about sockets.
> > > > 
> > > > A request is described by the task_diag_pid structure:
> > > > 
> > > > struct task_diag_pid {
> > > >        __u64   show_flags;      /* specify which information are required */
> > > >        __u64   dump_stratagy;   /* specify a group of processes */
> > > > 
> > > >        __u32   pid;
> > > > };
> > > 
> > > Can you explain how the interface relates to the 'taskstats' genetlink
> > > API? Did you consider extending that interface to provide the
> > > information you need instead of basing on the socket-diag?
> > 
> > It isn't based on the socket-diag, it looks like socket-diag.
> > 
> > Current task_diag registers a new genl family, but we can use the taskstats
> > family and add task_diag commands to it.
> 
> What I meant was more along the lines of making it look like taskstats
> by adding new fields to 'struct taskstat' for what you want return.
> I don't know if that is possible or a good idea for the information
> you want to get out of the kernel, but it seems like a more natural
> interface, as it already has some of the same data (comm, gid, pid,
> ppid, ...).

Now I see what you mean. task_diag has more flexible and universal
interface than taskstat. A response of taskstat only contains a
taskstats structure. A response of taskdiag can contains a few types of
properties. Each type is described by its own structure.

Curently here are only two groups of parameters: task_diag_msg and
task_diag_creds.

task_diag_msg contains a few basic parameters.
task_diag_creds contains credentials.

I'm going to add other groups to describe all kind of task properties
which currently are presented in procfs (e.g. /proc/pid/maps,
/proc/pid/fding/*, /proc/pid/status, etc).

One of features of task_diag is an ability to choose which information
are required. This allows to minimize a response size and a time, which
is requred to fill this response.

struct task_diag_msg {
        __u32   tgid;
        __u32   pid;
        __u32   ppid;
        __u32   tpid;
        __u32   sid;
        __u32   pgid;
        __u8    state;
        char    comm[TASK_DIAG_COMM_LEN];
};

struct task_diag_creds {
        struct task_diag_caps cap_inheritable;
        struct task_diag_caps cap_permitted;
        struct task_diag_caps cap_effective;
        struct task_diag_caps cap_bset;

        __u32 uid;
        __u32 euid;
        __u32 suid;
        __u32 fsuid;
        __u32 gid;
        __u32 egid;
        __u32 sgid;
        __u32 fsgid;
};

Thanks,
Andrew
> 
> 	Arnd
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