Commit 4614a696 authored by john stultz's avatar john stultz Committed by Linus Torvalds
Browse files

procfs: allow threads to rename siblings via /proc/pid/tasks/tid/comm 



Setting a thread's comm to be something unique is a very useful ability
and is helpful for debugging complicated threaded applications.  However
currently the only way to set a thread name is for the thread to name
itself via the PR_SET_NAME prctl.

However, there may be situations where it would be advantageous for a
thread dispatcher to be naming the threads its managing, rather then
having the threads self-describe themselves.  This sort of behavior is
available on other systems via the pthread_setname_np() interface.

This patch exports a task's comm via proc/pid/comm and
proc/pid/task/tid/comm interfaces, and allows thread siblings to write to
these values.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Mike Fulton <fultonm@ca.ibm.com>
Cc: Sean Foley <Sean_Foley@ca.ibm.com>
Cc: Darren Hart <dvhltc@us.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7e1e0ef2

Documentation/filesystems/proc.txt

+9 −0
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ Table of Contents 
  3.3	/proc/<pid>/io - Display the IO accounting fields

  3.4	/proc/<pid>/coredump_filter - Core dump filtering settings

  3.5	/proc/<pid>/mountinfo - Information about mounts

  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm





------------------------------------------------------------------------------
@@ -1409,3 +1410,11 @@ For more information on mount propagation see: 


  Documentation/filesystems/sharedsubtree.txt





3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm

--------------------------------------------------------

These files provide a method to access a tasks comm value. It also allows for

a task to set its own or one of its thread siblings comm value. The comm value

is limited in size compared to the cmdline value, so writing anything longer

then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated

comm value.

fs/exec.c

+9 −0
Original line number Diff line number Diff line
@@ -923,6 +923,15 @@ char *get_task_comm(char *buf, struct task_struct *tsk) 
void set_task_comm(struct task_struct *tsk, char *buf)

{

	task_lock(tsk);



	/*

	 * Threads may access current->comm without holding

	 * the task lock, so write the string carefully.

	 * Readers without a lock may see incomplete new

	 * names but are safe from non-terminating string reads.

	 */

	memset(tsk->comm, 0, TASK_COMM_LEN);

	wmb();

	strlcpy(tsk->comm, buf, sizeof(tsk->comm));

	task_unlock(tsk);

	perf_event_comm(tsk);

fs/proc/base.c

+68 −0
Original line number Diff line number Diff line
@@ -1265,6 +1265,72 @@ static const struct file_operations proc_pid_sched_operations = { 


#endif



static ssize_t comm_write(struct file *file, const char __user *buf,

				size_t count, loff_t *offset)

{

	struct inode *inode = file->f_path.dentry->d_inode;

	struct task_struct *p;

	char buffer[TASK_COMM_LEN];



	memset(buffer, 0, sizeof(buffer));

	if (count > sizeof(buffer) - 1)

		count = sizeof(buffer) - 1;

	if (copy_from_user(buffer, buf, count))

		return -EFAULT;



	p = get_proc_task(inode);

	if (!p)

		return -ESRCH;



	if (same_thread_group(current, p))

		set_task_comm(p, buffer);

	else

		count = -EINVAL;



	put_task_struct(p);



	return count;

}



static int comm_show(struct seq_file *m, void *v)

{

	struct inode *inode = m->private;

	struct task_struct *p;



	p = get_proc_task(inode);

	if (!p)

		return -ESRCH;



	task_lock(p);

	seq_printf(m, "%s\n", p->comm);

	task_unlock(p);



	put_task_struct(p);



	return 0;

}



static int comm_open(struct inode *inode, struct file *filp)

{

	int ret;



	ret = single_open(filp, comm_show, NULL);

	if (!ret) {

		struct seq_file *m = filp->private_data;



		m->private = inode;

	}

	return ret;

}



static const struct file_operations proc_pid_set_comm_operations = {

	.open		= comm_open,

	.read		= seq_read,

	.write		= comm_write,

	.llseek		= seq_lseek,

	.release	= single_release,

};



/*

 * We added or removed a vma mapping the executable. The vmas are only mapped

 * during exec and are not mapped with the mmap system call.
@@ -2504,6 +2570,7 @@ static const struct pid_entry tgid_base_stuff[] = { 
#ifdef CONFIG_SCHED_DEBUG

	REG("sched",      S_IRUGO|S_IWUSR, proc_pid_sched_operations),

#endif

	REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK

	INF("syscall",    S_IRUSR, proc_pid_syscall),

#endif
@@ -2838,6 +2905,7 @@ static const struct pid_entry tid_base_stuff[] = { 
#ifdef CONFIG_SCHED_DEBUG

	REG("sched",     S_IRUGO|S_IWUSR, proc_pid_sched_operations),

#endif

	REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK

	INF("syscall",   S_IRUSR, proc_pid_syscall),

#endif

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