Documentation/dynamic-debug-howto.txt


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Introduction
============

This document describes how to use the dynamic debug (ddebug) feature.

Dynamic debug is designed to allow you to dynamically enable/disable kernel
code to obtain additional kernel information. Currently, if
CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_debug() calls can be
dynamically enabled per-callsite.

Dynamic debug has even more useful features:

 * Simple query language allows turning on and off debugging statements by
   matching any combination of:

   - source filename
   - function name
   - line number (including ranges of line numbers)
   - module name
   - format string

 * Provides a debugfs control file: <debugfs>/dynamic_debug/control which can be
   read to display the complete list of known debug statements, to help guide you

Controlling dynamic debug Behaviour
===================================

The behaviour of pr_debug()/dev_debug()s are controlled via writing to a
control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
filesystem, in order to make use of this feature. Subsequently, we refer to the
control file as: <debugfs>/dynamic_debug/control. For example, if you want to
enable printing from source file 'svcsock.c', line 1603 you simply do:

nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
				<debugfs>/dynamic_debug/control

If you make a mistake with the syntax, the write will fail thus:

nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
				<debugfs>/dynamic_debug/control
-bash: echo: write error: Invalid argument

Viewing Dynamic Debug Behaviour
===========================

You can view the currently configured behaviour of all the debug statements
via:

nullarbor:~ # cat <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup - "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline       : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth         : %d\012"
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests     : %d\012"
...


You can also apply standard Unix text manipulation filters to this
data, e.g.

nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control  | wc -l
62

nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
42

Note in particular that the third column shows the enabled behaviour
flags for each debug statement callsite (see below for definitions of the
flags).  The default value, no extra behaviour enabled, is "-".  So
you can view all the debug statement callsites with any non-default flags:

nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"


Command Language Reference
==========================

At the lexical level, a command comprises a sequence of words separated
by whitespace characters.  Note that newlines are treated as word
separators and do *not* end a command or allow multiple commands to
be done together.  So these are all equivalent:

nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
				<debugfs>/dynamic_debug/control
nullarbor:~ # echo -c '  file   svcsock.c     line  1603 +p  ' >
				<debugfs>/dynamic_debug/control
nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' >
				<debugfs>/dynamic_debug/control
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
				<debugfs>/dynamic_debug/control

Commands are bounded by a write() system call.  If you want to do
multiple commands you need to do a separate "echo" for each, like:

nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\
> echo 'file svcsock.c line 1563 +p' > /proc/dprintk

or even like:

nullarbor:~ # (
> echo 'file svcsock.c line 1603 +p' ;\
> echo 'file svcsock.c line 1563 +p' ;\
> ) > /proc/dprintk

At the syntactical level, a command comprises a sequence of match
specifications, followed by a flags change specification.

command ::= match-spec* flags-spec

The match-spec's are used to choose a subset of the known dprintk()
callsites to which to apply the flags-spec.  Think of them as a query
with implicit ANDs between each pair.  Note that an empty list of
match-specs is possible, but is not very useful because it will not
match any debug statement callsites.

A match specification comprises a keyword, which controls the attribute
of the callsite to be compared, and a value to compare against.  Possible
keywords are:

match-spec ::= 'func' string |
	       'file' string |
	       'module' string |
	       'format' string |
	       'line' line-range

line-range ::= lineno |
	       '-'lineno |
	       lineno'-' |
	       lineno'-'lineno
// Note: line-range cannot contain space, e.g.
// "1-30" is valid range but "1 - 30" is not.

lineno ::= unsigned-int

The meanings of each keyword are:

func
    The given string is compared against the function name
    of each callsite.  Example:

    func svc_tcp_accept

file
    The given string is compared against either the full
    pathname or the basename of the source file of each
    callsite.  Examples:

    file svcsock.c
    file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c

module
    The given string is compared against the module name
    of each callsite.  The module name is the string as
    seen in "lsmod", i.e. without the directory or the .ko
    suffix and with '-' changed to '_'.  Examples:

    module sunrpc
    module nfsd

format
    The given string is searched for in the dynamic debug format
    string.  Note that the string does not need to match the
    entire format, only some part.  Whitespace and other
    special characters can be escaped using C octal character
    escape \ooo notation, e.g. the space character is \040.
    Alternatively, the string can be enclosed in double quote
    characters (") or single quote characters (').
    Examples:

    format svcrdma:	    // many of the NFS/RDMA server dprintks
    format readahead	    // some dprintks in the readahead cache
    format nfsd:\040SETATTR // one way to match a format with whitespace
    format "nfsd: SETATTR"  // a neater way to match a format with whitespace
    format 'nfsd: SETATTR'  // yet another way to match a format with whitespace

line
    The given line number or range of line numbers is compared
    against the line number of each dprintk() callsite.  A single
    line number matches the callsite line number exactly.  A
    range of line numbers matches any callsite between the first
    and last line number inclusive.  An empty first number means
    the first line in the file, an empty line number means the
    last number in the file.  Examples:

    line 1603	    // exactly line 1603
    line 1600-1605  // the six lines from line 1600 to line 1605
    line -1605	    // the 1605 lines from line 1 to line 1605
    line 1600-	    // all lines from line 1600 to the end of the file

The flags specification comprises a change operation followed
by one or more flag characters.  The change operation is one
of the characters:

-
    remove the given flags

+
    add the given flags

=
    set the flags to the given flags

The flags are:

f
    Include the function name in the printed message
l
    Include line number in the printed message
m
    Include module name in the printed message
p
    Causes a printk() message to be emitted to dmesg
t
    Include thread ID in messages not generated from interrupt context

Note the regexp ^[-+=][flmpt]+$ matches a flags specification.
Note also that there is no convenient syntax to remove all
the flags at once, you need to use "-flmpt".


Debug messages during boot process
==================================

To be able to activate debug messages during the boot process,
even before userspace and debugfs exists, use the boot parameter:
ddebug_query="QUERY"

QUERY follows the syntax described above, but must not exceed 1023
characters. The enablement of debug messages is done as an arch_initcall.
Thus you can enable debug messages in all code processed after this
arch_initcall via this boot parameter.
On an x86 system for example ACPI enablement is a subsys_initcall and
ddebug_query="file ec.c +p"
will show early Embedded Controller transactions during ACPI setup if
your machine (typically a laptop) has an Embedded Controller.
PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.


Examples
========

// enable the message at line 1603 of file svcsock.c
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
				<debugfs>/dynamic_debug/control

// enable all the messages in file svcsock.c
nullarbor:~ # echo -n 'file svcsock.c +p' >
				<debugfs>/dynamic_debug/control

// enable all the messages in the NFS server module
nullarbor:~ # echo -n 'module nfsd +p' >
				<debugfs>/dynamic_debug/control

// enable all 12 messages in the function svc_process()
nullarbor:~ # echo -n 'func svc_process +p' >
				<debugfs>/dynamic_debug/control

// disable all 12 messages in the function svc_process()
nullarbor:~ # echo -n 'func svc_process -p' >
				<debugfs>/dynamic_debug/control

// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
				<debugfs>/dynamic_debug/control
/*
 * This file contains the procedures for the handling of select and poll
 *
 * Created for Linux based loosely upon Mathius Lattner's minix
 * patches by Peter MacDonald. Heavily edited by Linus.
 *
 *  4 February 1994
 *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS
 *     flag set in its personality we do *not* modify the given timeout
 *     parameter to reflect time remaining.
 *
 *  24 January 2000
 *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation 
 *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/personality.h> /* for STICKY_TIMEOUTS */
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/fs.h>
#include <linux/rcupdate.h>
#include <linux/hrtimer.h>

#include <asm/uaccess.h>


/*
 * Estimate expected accuracy in ns from a timeval.
 *
 * After quite a bit of churning around, we've settled on
 * a simple thing of taking 0.1% of the timeout as the
 * slack, with a cap of 100 msec.
 * "nice" tasks get a 0.5% slack instead.
 *
 * Consider this comment an open invitation to come up with even
 * better solutions..
 */

#define MAX_SLACK	(100 * NSEC_PER_MSEC)

static long __estimate_accuracy(struct timespec *tv)
{
	long slack;
	int divfactor = 1000;

	if (tv->tv_sec < 0)
		return 0;

	if (task_nice(current) > 0)
		divfactor = divfactor / 5;

	if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))
		return MAX_SLACK;

	slack = tv->tv_nsec / divfactor;
	slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);

	if (slack > MAX_SLACK)
		return MAX_SLACK;

	return slack;
}

long select_estimate_accuracy(struct timespec *tv)
{
	unsigned long ret;
	struct timespec now;

	/*
	 * Realtime tasks get a slack of 0 for obvious reasons.
	 */

	if (rt_task(current))
		return 0;

	ktime_get_ts(&now);
	now = timespec_sub(*tv, now);
	ret = __estimate_accuracy(&now);
	if (ret < current->timer_slack_ns)
		return current->timer_slack_ns;
	return ret;
}


struct poll_table_page {
	struct poll_table_page * next;
	struct poll_table_entry * entry;
	struct poll_table_entry entries[0];
};

#define POLL_TABLE_FULL(table) \
	((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))

/*
 * Ok, Peter made a complicated, but straightforward multiple_wait() function.
 * I have rewritten this, taking some shortcuts: This code may not be easy to
 * follow, but it should be free of race-conditions, and it's practical. If you
 * understand what I'm doing here, then you understand how the linux
 * sleep/wakeup mechanism works.
 *
 * Two very simple procedures, poll_wait() and poll_freewait() make all the
 * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
 * as all select/poll functions have to call it to add an entry to the
 * poll table.
 */
static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
		       poll_table *p);

void poll_initwait(struct poll_wqueues *pwq)
{
	init_poll_funcptr(&pwq->pt, __pollwait);
	pwq->polling_task = current;
	pwq->triggered = 0;
	pwq->error = 0;
	pwq->table = NULL;
	pwq->inline_index = 0;
}
EXPORT_SYMBOL(poll_initwait);

static void free_poll_entry(struct poll_table_entry *entry)
{
	remove_wait_queue(entry->wait_address, &entry->wait);
	fput(entry->filp);
}

void poll_freewait(struct poll_wqueues *pwq)
{
	struct poll_table_page * p = pwq->table;
	int i;
	for (i = 0; i < pwq->inline_index; i++)
		free_poll_entry(pwq->inline_entries + i);
	while (p) {
		struct poll_table_entry * entry;
		struct poll_table_page *old;

		entry = p->entry;
		do {
			entry--;
			free_poll_entry(entry);
		} while (entry > p->entries);
		old = p;
		p = p->next;
		free_page((unsigned long) old);
	}
}
EXPORT_SYMBOL(poll_freewait);

static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
{
	struct poll_table_page *table = p->table;

	if (p->inline_index < N_INLINE_POLL_ENTRIES)
		return p->inline_entries + p->inline_index++;

	if (!table || POLL_TABLE_FULL(table)) {
		struct poll_table_page *new_table;

		new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
		if (!new_table) {
			p->error = -ENOMEM;
			return NULL;
		}
		new_table->entry = new_table->entries;
		new_table->next = table;
		p->table = new_table;
		table = new_table;
	}

	return table->entry++;
}

static int __pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
	struct poll_wqueues *pwq = wait->private;
	DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);

	/*
	 * Although this function is called under waitqueue lock, LOCK
	 * doesn't imply write barrier and the users expect write
	 * barrier semantics on wakeup functions.  The following
	 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
	 * and is paired with set_mb() in poll_schedule_timeout.
	 */
	smp_wmb();
	pwq->triggered = 1;

	/*
	 * Perform the default wake up operation using a dummy
	 * waitqueue.
	 *
	 * TODO: This is hacky but there currently is no interface to
	 * pass in @sync.  @sync is scheduled to be removed and once
	 * that happens, wake_up_process() can be used directly.
	 */
	return default_wake_function(&dummy_wait, mode, sync, key);
}

static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
	struct poll_table_entry *entry;

	entry = container_of(wait, struct poll_table_entry, wait);
	if (key && !((unsigned long)key & entry->key))
		return 0;
	return __pollwake(wait, mode, sync, key);
}

/* Add a new entry */
static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
				poll_table *p)
{
	struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
	struct poll_table_entry *entry = poll_get_entry(pwq);
	if (!entry)
		return;
	get_file(filp);
	entry->filp = filp;
	entry->wait_address = wait_address;
	entry->key = p->key;
	init_waitqueue_func_entry(&entry->wait, pollwake);
	entry->wait.private = pwq;
	add_wait_queue(wait_address, &entry->wait);
}

int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
			  ktime_t *expires, unsigned long slack)
{
	int rc = -EINTR;

	set_current_state(state);
	if (!pwq->triggered)
		rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
	__set_current_state(TASK_RUNNING);

	/*
	 * Prepare for the next iteration.
	 *
	 * The following set_mb() serves two purposes.  First, it's
	 * the counterpart rmb of the wmb in pollwake() such that data
	 * written before wake up is always visible after wake up.
	 * Second, the full barrier guarantees that triggered clearing
	 * doesn't pass event check of the next iteration.  Note that
	 * this problem doesn't exist for the first iteration as
	 * add_wait_queue() has full barrier semantics.
	 */
	set_mb(pwq->triggered, 0);

	return rc;
}
EXPORT_SYMBOL(poll_schedule_timeout);

/**
 * poll_select_set_timeout - helper function to setup the timeout value
 * @to:		pointer to timespec variable for the final timeout
 * @sec:	seconds (from user space)
 * @nsec:	nanoseconds (from user space)
 *
 * Note, we do not use a timespec for the user space value here, That
 * way we can use the function for timeval and compat interfaces as well.
 *
 * Returns -EINVAL if sec/nsec are not normalized. Otherwise 0.
 */
int poll_select_set_timeout(struct timespec *to, long sec, long nsec)
{
	struct timespec ts = {.tv_sec = sec, .tv_nsec = nsec};

	if (!timespec_valid(&ts))
		return -EINVAL;

	/* Optimize for the zero timeout value here */
	if (!sec && !nsec) {
		to->tv_sec = to->tv_nsec = 0;
	} else {
		ktime_get_ts(to);
		*to = timespec_add_safe(*to, ts);
	}
	return 0;
}

static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
				      int timeval, int ret)
{
	struct timespec rts;
	struct timeval rtv;

	if (!p)
		return ret;

	if (current->personality & STICKY_TIMEOUTS)
		goto sticky;

	/* No update for zero timeout */
	if (!end_time->tv_sec && !end_time->tv_nsec)
		return ret;

	ktime_get_ts(&rts);
	rts = timespec_sub(*end_time, rts);
	if (rts.tv_sec < 0)
		rts.tv_sec = rts.tv_nsec = 0;

	if (timeval) {
		if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
			memset(&rtv, 0, sizeof(rtv));
		rtv.tv_sec = rts.tv_sec;
		rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;

		if (!copy_to_user(p, &rtv, sizeof(rtv)))
			return ret;

	} else if (!copy_to_user(p, &rts, sizeof(rts)))
		return ret;

	/*
	 * If an application puts its timeval in read-only memory, we
	 * don't want the Linux-specific update to the timeval to
	 * cause a fault after the select has completed
	 * successfully. However, because we're not updating the
	 * timeval, we can't restart the system call.
	 */

sticky:
	if (ret == -ERESTARTNOHAND)
		ret = -EINTR;
	return ret;
}

#define FDS_IN(fds, n)		(fds->in + n)
#define FDS_OUT(fds, n)		(fds->out + n)
#define FDS_EX(fds, n)		(fds->ex + n)

#define BITS(fds, n)	(*FDS_IN(fds, n)|*FDS_OUT(fds, n)|*FDS_EX(fds, n))

static int max_select_fd(unsigned long n, fd_set_bits *fds)
{
	unsigned long *open_fds;
	unsigned long set;
	int max;
	struct fdtable *fdt;

	/* handle last in-complete long-word first */
	set = ~(~0UL << (n & (__NFDBITS-1)));
	n /= __NFDBITS;
	fdt = files_fdtable(current->files);
	open_fds = fdt->open_fds->fds_bits+n;
	max = 0;
	if (set) {
		set &= BITS(fds, n);
		if (set) {
			if (!(set & ~*open_fds))
				goto get_max;
			return -EBADF;
		}
	}
	while (n) {
		open_fds--;
		n--;
		set = BITS(fds, n);
		if (!set)
			continue;
		if (set & ~*open_fds)
			return -EBADF;
		if (max)
			continue;
get_max:
		do {
			max++;
			set >>= 1;
		} while (set);
		max += n * __NFDBITS;
	}

	return max;
}

#define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
#define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
#define POLLEX_SET (POLLPRI)

static inline void wait_key_set(poll_table *wait, unsigned long in,
				unsigned long out, unsigned long bit)
{
	if (wait) {
		wait->key = POLLEX_SET;
		if (in & bit)
			wait->key |= POLLIN_SET;
		if (out & bit)
			wait->key |= POLLOUT_SET;
	}
}

int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
{
	ktime_t expire, *to = NULL;
	struct poll_wqueues table;
	poll_table *wait;
	int retval, i, timed_out = 0;
	unsigned long slack = 0;

	rcu_read_lock();
	retval = max_select_fd(n, fds);
	rcu_read_unlock();

	if (retval < 0)
		return retval;
	n = retval;

	poll_initwait(&table);
	wait = &table.pt;
	if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
		wait = NULL;
		timed_out = 1;
	}

	if (end_time && !timed_out)
		slack = select_estimate_accuracy(end_time);

	retval = 0;
	for (;;) {
		unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;

		inp = fds->in; outp = fds->out; exp = fds->ex;
		rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;

		for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
			unsigned long in, out, ex, all_bits, bit = 1, mask, j;
			unsigned long res_in = 0, res_out = 0, res_ex = 0;
			const struct file_operations *f_op = NULL;
			struct file *file = NULL;

			in = *inp++; out = *outp++; ex = *exp++;
			all_bits = in | out | ex;
			if (all_bits == 0) {
				i += __NFDBITS;
				continue;
			}

			for (j = 0; j < __NFDBITS; ++j, ++i, bit <<= 1) {
				int fput_needed;
				if (i >= n)
					break;
				if (!(bit & all_bits))
					continue;
				file = fget_light(i, &fput_needed);
				if (file) {
					f_op = file->f_op;
					mask = DEFAULT_POLLMASK;
					if (f_op && f_op->poll) {
						wait_key_set(wait, in, out, bit);
						mask = (*f_op->poll)(file, wait);
					}
					fput_light(file, fput_needed);
					if ((mask & POLLIN_SET) && (in & bit)) {
						res_in |= bit;
						retval++;
						wait = NULL;
					}
					if ((mask & POLLOUT_SET) && (out & bit)) {
						res_out |= bit;
						retval++;
						wait = NULL;
					}
					if ((mask & POLLEX_SET) && (ex & bit)) {
						res_ex |= bit;
						retval++;
						wait = NULL;
					}
				}
			}
			if (res_in)
				*rinp = res_in;
			if (res_out)
				*routp = res_out;
			if (res_ex)
				*rexp = res_ex;
			cond_resched();
		}
		wait = NULL;
		if (retval || timed_out || signal_pending(current))
			break;
		if (table.error) {
			retval = table.error;
			break;
		}

		/*
		 * If this is the first loop and we have a timeout
		 * given, then we convert to ktime_t and set the to
		 * pointer to the expiry value.
		 */
		if (end_time && !to) {
			expire = timespec_to_ktime(*end_time);
			to = &expire;
		}

		if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
					   to, slack))
			timed_out = 1;
	}

	poll_freewait(&table);

	return retval;
}

/*
 * We can actually return ERESTARTSYS instead of EINTR, but I'd
 * like to be certain this leads to no problems. So I return
 * EINTR just for safety.
 *
 * Update: ERESTARTSYS breaks at least the xview clock binary, so
 * I'm trying ERESTARTNOHAND which restart only when you want to.
 */
int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
			   fd_set __user *exp, struct timespec *end_time)
{
	fd_set_bits fds;
	void *bits;
	int ret, max_fds;
	unsigned int size;
	struct fdtable *fdt;
	/* Allocate small arguments on the stack to save memory and be faster */
	long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];

	ret = -EINVAL;
	if (n < 0)
		goto out_nofds;

	/* max_fds can increase, so grab it once to avoid race */
	rcu_read_lock();
	fdt = files_fdtable(current->files);
	max_fds = fdt->max_fds;
	rcu_read_unlock();
	if (n > max_fds)
		n = max_fds;

	/*
	 * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
	 * since we used fdset we need to allocate memory in units of
	 * long-words. 
	 */
	size = FDS_BYTES(n);
	bits = stack_fds;
	if (size > sizeof(stack_fds) / 6) {
		/* Not enough space in on-stack array; must use kmalloc */
		ret = -ENOMEM;
		bits = kmalloc(6 * size, GFP_KERNEL);
		if (!bits)
			goto out_nofds;
	}
	fds.in      = bits;
	fds.out     = bits +   size;
	fds.ex      = bits + 2*size;
	fds.res_in  = bits + 3*size;
	fds.res_out = bits + 4*size;
	fds.res_ex  = bits + 5*size;

	if ((ret = get_fd_set(n, inp, fds.in)) ||
	    (ret = get_fd_set(n, outp, fds.out)) ||
	    (ret = get_fd_set(n, exp, fds.ex)))
		goto out;
	zero_fd_set(n, fds.res_in);
	zero_fd_set(n, fds.res_out);
	zero_fd_set(n, fds.res_ex);

	ret = do_select(n, &fds, end_time);

	if (ret < 0)
		goto out;
	if (!ret) {
		ret = -ERESTARTNOHAND;
		if (signal_pending(current))
			goto out;
		ret = 0;
	}

	if (set_fd_set(n, inp, fds.res_in) ||
	    set_fd_set(n, outp, fds.res_out) ||
	    set_fd_set(n, exp, fds.res_ex))
		ret = -EFAULT;

out:
	if (bits != stack_fds)
		kfree(bits);
out_nofds:
	return ret;
}

SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
		fd_set __user *, exp, struct timeval __user *, tvp)
{
	struct timespec end_time, *to = NULL;
	struct timeval tv;
	int ret;

	if (tvp) {
		if (copy_from_user(&tv, tvp, sizeof(tv)))
			return -EFAULT;

		to = &end_time;
		if (poll_select_set_timeout(to,
				tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),
				(tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC))
			return -EINVAL;
	}

	ret = core_sys_select(n, inp, outp, exp, to);
	ret = poll_select_copy_remaining(&end_time, tvp, 1, ret);

	return ret;
}

#ifdef HAVE_SET_RESTORE_SIGMASK
static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
		       fd_set __user *exp, struct timespec __user *tsp,
		       const sigset_t __user *sigmask, size_t sigsetsize)
{
	sigset_t ksigmask, sigsaved;
	struct timespec ts, end_time, *to = NULL;
	int ret;

	if (tsp) {
		if (copy_from_user(&ts, tsp, sizeof(ts)))
			return -EFAULT;

		to = &end_time;
		if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
			return -EINVAL;
	}

	if (sigmask) {
		/* XXX: Don't preclude handling different sized sigset_t's.  */
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
			return -EFAULT;

		sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
		sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
	}

	ret = core_sys_select(n, inp, outp, exp, to);
	ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);

	if (ret == -ERESTARTNOHAND) {
		/*
		 * Don't restore the signal mask yet. Let do_signal() deliver
		 * the signal on the way back to userspace, before the signal
		 * mask is restored.
		 */
		if (sigmask) {
			memcpy(&current->saved_sigmask, &sigsaved,
					sizeof(sigsaved));
			set_restore_sigmask();
		}
	} else if (sigmask)
		sigprocmask(SIG_SETMASK, &sigsaved, NULL);

	return ret;
}

/*
 * Most architectures can't handle 7-argument syscalls. So we provide a
 * 6-argument version where the sixth argument is a pointer to a structure
 * which has a pointer to the sigset_t itself followed by a size_t containing
 * the sigset size.
 */
SYSCALL_DEFINE6(pselect6, int, n, fd_set __user *, inp, fd_set __user *, outp,
		fd_set __user *, exp, struct timespec __user *, tsp,
		void __user *, sig)
{
	size_t sigsetsize = 0;
	sigset_t __user *up = NULL;

	if (sig) {
		if (!access_ok(VERIFY_READ, sig, sizeof(void *)+sizeof(size_t))
		    || __get_user(up, (sigset_t __user * __user *)sig)
		    || __get_user(sigsetsize,
				(size_t __user *)(sig+sizeof(void *))))
			return -EFAULT;
	}

	return do_pselect(n, inp, outp, exp, tsp, up, sigsetsize);
}
#endif /* HAVE_SET_RESTORE_SIGMASK */

#ifdef __ARCH_WANT_SYS_OLD_SELECT
struct sel_arg_struct {
	unsigned long n;
	fd_set __user *inp, *outp, *exp;
	struct timeval __user *tvp;
};

SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg)
{
	struct sel_arg_struct a;

	if (copy_from_user(&a, arg, sizeof(a)))
		return -EFAULT;
	return sys_select(a.n, a.inp, a.outp, a.exp, a.tvp);
}
#endif

struct poll_list {
	struct poll_list *next;
	int len;
	struct pollfd entries[0];
};

#define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))

/*
 * Fish for pollable events on the pollfd->fd file descriptor. We're only
 * interested in events matching the pollfd->events mask, and the result
 * matching that mask is both recorded in pollfd->revents and returned. The
 * pwait poll_table will be used by the fd-provided poll handler for waiting,
 * if non-NULL.
 */
static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
{
	unsigned int mask;
	int fd;

	mask = 0;
	fd = pollfd->fd;
	if (fd >= 0) {
		int fput_needed;
		struct file * file;

		file = fget_light(fd, &fput_needed);
		mask = POLLNVAL;
		if (file != NULL) {
			mask = DEFAULT_POLLMASK;
			if (file->f_op && file->f_op->poll) {
				if (pwait)
					pwait->key = pollfd->events |
							POLLERR | POLLHUP;
				mask = file->f_op->poll(file, pwait);
			}
			/* Mask out unneeded events. */
			mask &= pollfd->events | POLLERR | POLLHUP;
			fput_light(file, fput_needed);
		}
	}
	pollfd->revents = mask;

	return mask;
}

static int do_poll(unsigned int nfds,  struct poll_list *list,
		   struct poll_wqueues *wait, struct timespec *end_time)
{
	poll_table* pt = &wait->pt;
	ktime_t expire, *to = NULL;
	int timed_out = 0, count = 0;
	unsigned long slack = 0;

	/* Optimise the no-wait case */
	if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
		pt = NULL;
		timed_out = 1;
	}

	if (end_time && !timed_out)
		slack = select_estimate_accuracy(end_time);

	for (;;) {
		struct poll_list *walk;

		for (walk = list; walk != NULL; walk = walk->next) {
			struct pollfd * pfd, * pfd_end;

			pfd = walk->entries;
			pfd_end = pfd + walk->len;
			for (; pfd != pfd_end; pfd++) {
				/*
				 * Fish for events. If we found one, record it
				 * and kill the poll_table, so we don't
				 * needlessly register any other waiters after
				 * this. They'll get immediately deregistered
				 * when we break out and return.
				 */
				if (do_pollfd(pfd, pt)) {
					count++;
					pt = NULL;
				}
			}
		}
		/*
		 * All waiters have already been registered, so don't provide
		 * a poll_table to them on the next loop iteration.
		 */
		pt = NULL;
		if (!count) {
			count = wait->error;
			if (signal_pending(current))
				count = -EINTR;
		}
		if (count || timed_out)
			break;

		/*
		 * If this is the first loop and we have a timeout
		 * given, then we convert to ktime_t and set the to
		 * pointer to the expiry value.
		 */
		if (end_time && !to) {
			expire = timespec_to_ktime(*end_time);
			to = &expire;
		}

		if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
			timed_out = 1;
	}
	return count;
}

#define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / \
			sizeof(struct pollfd))

int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
		struct timespec *end_time)
{
	struct poll_wqueues table;
 	int err = -EFAULT, fdcount, len, size;
	/* Allocate small arguments on the stack to save memory and be
	   faster - use long to make sure the buffer is aligned properly
	   on 64 bit archs to avoid unaligned access */
	long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
	struct poll_list *const head = (struct poll_list *)stack_pps;
 	struct poll_list *walk = head;
 	unsigned long todo = nfds;

	if (nfds > rlimit(RLIMIT_NOFILE))
		return -EINVAL;

	len = min_t(unsigned int, nfds, N_STACK_PPS);
	for (;;) {
		walk->next = NULL;
		walk->len = len;
		if (!len)
			break;

		if (copy_from_user(walk->entries, ufds + nfds-todo,
					sizeof(struct pollfd) * walk->len))
			goto out_fds;

		todo -= walk->len;
		if (!todo)
			break;

		len = min(todo, POLLFD_PER_PAGE);
		size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
		walk = walk->next = kmalloc(size, GFP_KERNEL);
		if (!walk) {
			err = -ENOMEM;
			goto out_fds;
		}
	}

	poll_initwait(&table);
	fdcount = do_poll(nfds, head, &table, end_time);
	poll_freewait(&table);

	for (walk = head; walk; walk = walk->next) {
		struct pollfd *fds = walk->entries;
		int j;

		for (j = 0; j < walk->len; j++, ufds++)
			if (__put_user(fds[j].revents, &ufds->revents))
				goto out_fds;
  	}

	err = fdcount;
out_fds:
	walk = head->next;
	while (walk) {
		struct poll_list *pos = walk;
		walk = walk->next;
		kfree(pos);
	}

	return err;
}

static long do_restart_poll(struct restart_block *restart_block)
{
	struct pollfd __user *ufds = restart_block->poll.ufds;
	int nfds = restart_block->poll.nfds;
	struct timespec *to = NULL, end_time;
	int ret;

	if (restart_block->poll.has_timeout) {
		end_time.tv_sec = restart_block->poll.tv_sec;
		end_time.tv_nsec = restart_block->poll.tv_nsec;
		to = &end_time;
	}

	ret = do_sys_poll(ufds, nfds, to);

	if (ret == -EINTR) {
		restart_block->fn = do_restart_poll;
		ret = -ERESTART_RESTARTBLOCK;
	}
	return ret;
}

SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
		long, timeout_msecs)
{
	struct timespec end_time, *to = NULL;
	int ret;

	if (timeout_msecs >= 0) {
		to = &end_time;
		poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
			NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
	}

	ret = do_sys_poll(ufds, nfds, to);

	if (ret == -EINTR) {
		struct restart_block *restart_block;

		restart_block = &current_thread_info()->restart_block;
		restart_block->fn = do_restart_poll;
		restart_block->poll.ufds = ufds;
		restart_block->poll.nfds = nfds;

		if (timeout_msecs >= 0) {
			restart_block->poll.tv_sec = end_time.tv_sec;
			restart_block->poll.tv_nsec = end_time.tv_nsec;
			restart_block->poll.has_timeout = 1;
		} else
			restart_block->poll.has_timeout = 0;

		ret = -ERESTART_RESTARTBLOCK;
	}
	return ret;
}

#ifdef HAVE_SET_RESTORE_SIGMASK
SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
		struct timespec __user *, tsp, const sigset_t __user *, sigmask,
		size_t, sigsetsize)
{
	sigset_t ksigmask, sigsaved;
	struct timespec ts, end_time, *to = NULL;
	int ret;

	if (tsp) {
		if (copy_from_user(&ts, tsp, sizeof(ts)))
			return -EFAULT;

		to = &end_time;
		if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
			return -EINVAL;
	}

	if (sigmask) {
		/* XXX: Don't preclude handling different sized sigset_t's.  */
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
			return -EFAULT;

		sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
		sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
	}

	ret = do_sys_poll(ufds, nfds, to);

	/* We can restart this syscall, usually */
	if (ret == -EINTR) {
		/*
		 * Don't restore the signal mask yet. Let do_signal() deliver
		 * the signal on the way back to userspace, before the signal
		 * mask is restored.
		 */
		if (sigmask) {
			memcpy(&current->saved_sigmask, &sigsaved,
					sizeof(sigsaved));
			set_restore_sigmask();
		}
		ret = -ERESTARTNOHAND;
	} else if (sigmask)
		sigprocmask(SIG_SETMASK, &sigsaved, NULL);

	ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);

	return ret;
}
#endif /* HAVE_SET_RESTORE_SIGMASK */