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Message-ID: <20050111104919.64122.qmail@web60603.mail.yahoo.com>
Date: Tue, 11 Jan 2005 02:49:19 -0800 (PST)
From: selvakumar nagendran <kernelselva@yahoo.com>
Subject: pipe_wait illustration needed
To: linux-kernel@vger.kernel.org
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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Lines: 43

Hello linux-experts,
    I can't understand this function pipe_wait defined
in linux/fs/pipe.c line by line,especially the lines
after add_wait_queue. If the process is added to the
wait queue and schedule() is called then after that a
new process will be selected and will be given the
CPU. So, the current process will be out of the way.
Then, how can the kernel reach the line 
remove_wait_queue. 
    Also, how the scheduler will know that the pipe
event has occurred and it's safe to set the process
state to TASK_RUNNING?

Thanks,
selva
----------------
/* Drop the inode semaphore and wait for a pipe event,
atomically */
void pipe_wait(struct inode * inode)
{
	DECLARE_WAITQUEUE(wait, current);
	current->state = TASK_INTERRUPTIBLE;
	add_wait_queue(PIPE_WAIT(*inode), &wait);
	up(PIPE_SEM(*inode));
	schedule();
	remove_wait_queue(PIPE_WAIT(*inode), &wait);
	current->state = TASK_RUNNING;
	down(PIPE_SEM(*inode));
}


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