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SubjectRe: [PATCH 2.6.12-rc3-mm3] connector: add a fork connector
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On Mon, 2005-05-09 at 15:57 +0200, Alexander Nyberg wrote:
> > +static inline void cn_fork_send_status(void)
> > +{
> > + /* TODO: An informational line in log is maybe not enough... */
> > + printk(KERN_INFO "cn_fork_enable == %d\n", cn_fork_enable);
> > +}
> > +
> > +/**
> > + * cn_fork_callback - enable or disable the fork connector
> > + * @data: message send by the connector
> > + *
> > + * The callback allows to enable or disable the sending of information
> > + * about fork in the do_fork() routine. To enable the fork, the user
> > + * space application must send the integer 1 in the data part of the
> > + * message. To disable the fork connector, it must send the integer 0.
> > + */
> > +static void cn_fork_callback(void *data)
> > +{
> > + struct cn_msg *msg = data;
> > + int action;
> > +
> > + if (cn_already_initialized && (msg->len == sizeof(cn_fork_enable))) {
> > + memcpy(&action, msg->data, sizeof(cn_fork_enable));
> > + switch(action) {
> > + case FORK_CN_START:
> > + cn_fork_enable = 1;
> > + break;
> > + case FORK_CN_STOP:
> > + cn_fork_enable = 0;
> > + break;
> > + case FORK_CN_STATUS:
> > + cn_fork_send_status();
>
> Why does this not pass down the status to the app asking about it
> instead?

I don't know exactly how to do that. A solution could be to send a
message through the connector. I think about using the following
structure:

#define FORK_CN_MSG_P 0 /* Information is about processes */
#define FORK_CN_MSG_S 1 /* Information is about status */

/*
* The fork connector sends information to a user-space
* application. From the user's point of view, the process
* ID is the thread group ID and thread ID is the internal
* kernel "pid". So, fields are assigned as follow:
*
* In user space - In kernel space
*
* parent process ID = parent->tgid
* parent thread ID = parent->pid
* child process ID = child->tgid
* child thread ID = child->pid
*/
struct cn_fork_msg {
int type; /* 0: information about fork
1: information about the status */
int cpu; /* ID of the cpu where the fork occured */
union {
struct {
pid_t ppid; /* parent process ID */
pid_t ptid; /* parent thread ID */
pid_t cpid; /* child process ID */
pid_t ctid; /* child thread ID */
};
int status;
};
};

And then, the cn_fork_send_status() could be coded as follow:

/**
* cn_fork_send_status - send a message with the status
*/
static inline void cn_fork_send_status(void)
{
struct cn_msg *msg;
struct cn_fork_msg *forkmsg;
__u8 buffer[CN_FORK_MSG_SIZE];

msg = (struct cn_msg *)buffer;

memcpy(&msg->id, &cb_fork_id, sizeof(msg->id));

msg->ack = 0; /* not used */
msg->seq = 0; /* not used */

msg->len = CN_FORK_INFO_SIZE;
forkmsg = (struct cn_fork_msg *)msg->data;
forkmsg->type = FORK_CN_MSG_S;
forkmsg->status = cn_fork_enable;

cn_netlink_send(msg, CN_IDX_FORK, GFP_KERNEL);
}

I think this solution is good. Agree?

Best,
Guillaume.

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