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:

quoted

On Tue, Feb 17, 2015 at 09:53:09AM +0100, Arnd Bergmann wrote:

quoted

On Tuesday 17 February 2015 11:20:19 Andrey Vagin wrote:

quoted

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