Re: Pollable Semaphores

From: Chris Wright (chrisw_at_osdl.org)
Date: 01/22/05

  • Next message: Con Kolivas: "Re: [PATCH]sched: Isochronous class v2 for unprivileged soft rt scheduling" 
    Date:	Fri, 21 Jan 2005 23:05:04 -0800
To: Ulrich Drepper <drepper@gmail.com>

    * Chris Wright (chrisw@osdl.org) wrote:
    > * Ulrich Drepper (drepper@gmail.com) wrote:
    > > And is another thing to consider. There is at least one other event
    > > which should be pollable: process (maybe threads) deaths. I was
    > > hoping that we get support for this, perhaps in the form of polling
    > > the /proc/PID directory. For poll(), a POLLERR value could mean the
    > > process/thread died. For select(), once again a bit in the except
    > > array could be set.
    >
    > I have a simple patch that does just that. It worked after brief testing,
    > then I never went back to look at it any more. I'll see if I can't dig
    > it up, maybe it's useful.

    Yeah, here it is. I refreshed it against a current kernel. It passes my
    same old test, where I select on /proc/<pid>/status fd in exceptfds.

    ===== fs/proc/base.c 1.86 vs edited =====
    --- 1.86/fs/proc/base.c 2005-01-10 17:29:31 -08:00
    +++ edited/fs/proc/base.c 2005-01-21 22:51:00 -08:00
    @@ -32,6 +32,7 @@
     #include <linux/mount.h>
     #include <linux/security.h>
     #include <linux/ptrace.h>
    +#include <linux/poll.h>
     #include "internal.h"
     
     /*
    @@ -519,8 +520,21 @@ static ssize_t proc_info_read(struct fil
             return length;
     }
     
    +static unsigned int proc_info_poll(struct file *file, poll_table *wait)
    +{
    + struct inode *inode = file->f_dentry->d_inode;
    + struct task_struct *task = proc_task(inode);
    + wait_queue_head_t *pid_wait = &PROC_I(task->proc_dentry->d_inode)->wait;
    +
    + poll_wait(file, pid_wait, wait);
    + if (!pid_alive(task))
    + return POLLPRI;
    + return 0;
    +}
    +
     static struct file_operations proc_info_file_operations = {
             .read = proc_info_read,
    + .poll = proc_info_poll,
     };
     
     static int mem_open(struct inode* inode, struct file* file)
    @@ -1489,6 +1503,8 @@ void proc_pid_flush(struct dentry *proc_
     {
             might_sleep();
             if(proc_dentry != NULL) {
    + wait_queue_head_t *pid_wait=&PROC_I(proc_dentry->d_inode)->wait;
    + wake_up_interruptible(pid_wait);
                     shrink_dcache_parent(proc_dentry);
                     dput(proc_dentry);
             }
    ===== fs/proc/inode.c 1.31 vs edited =====
    --- 1.31/fs/proc/inode.c 2005-01-04 18:48:14 -08:00
    +++ edited/fs/proc/inode.c 2005-01-21 22:48:06 -08:00
    @@ -97,6 +97,7 @@ static struct inode *proc_alloc_inode(st
             ei->type = 0;
             ei->op.proc_get_link = NULL;
             ei->pde = NULL;
    + init_waitqueue_head(&ei->wait);
             inode = &ei->vfs_inode;
             inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
             return inode;
    ===== include/linux/proc_fs.h 1.41 vs edited =====
    --- 1.41/include/linux/proc_fs.h 2005-01-07 21:44:33 -08:00
    +++ edited/include/linux/proc_fs.h 2005-01-21 22:48:06 -08:00
    @@ -243,6 +243,7 @@ struct proc_inode {
                     int (*proc_read)(struct task_struct *task, char *page);
             } op;
             struct proc_dir_entry *pde;
    + wait_queue_head_t wait;
             struct inode vfs_inode;
     };
     
    -
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  • Next message: Con Kolivas: "Re: [PATCH]sched: Isochronous class v2 for unprivileged soft rt scheduling"

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