/*
   * 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/export.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 <linux/sched/rt.h>

  #include <linux/freezer.h>

  #include <net/busy_poll.h>

  #include <linux/vmalloc.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 timespec64 *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;
  }

  u64 select_estimate_accuracy(struct timespec64 *tv)

  {

  	u64 ret;

  	struct timespec64 now;

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

  	if (rt_task(current))

  		return 0;

  	ktime_get_ts64(&now);
  	now = timespec64_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 smp_store_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;

  	entry->filp = get_file(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 smp_store_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.
  	 */

  	smp_store_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 timespec64 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 timespec64 *to, time64_t sec, long nsec)

  {

  	struct timespec64 ts = {.tv_sec = sec, .tv_nsec = nsec};

  	if (!timespec64_valid(&ts))

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

  		ktime_get_ts64(to);
  		*to = timespec64_add_safe(*to, ts);

  	}
  	return 0;
  }

  static int poll_select_copy_remaining(struct timespec64 *end_time,
  				      void __user *p,

  				      int timeval, int ret)
  {

  	struct timespec64 rts64;

  	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_ts64(&rts64);
  	rts64 = timespec64_sub(*end_time, rts64);
  	if (rts64.tv_sec < 0)
  		rts64.tv_sec = rts64.tv_nsec = 0;
  
  	rts = timespec64_to_timespec(rts64);

  
  	if (timeval) {

  		if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
  			memset(&rtv, 0, sizeof(rtv));

  		rtv.tv_sec = rts64.tv_sec;
  		rtv.tv_usec = rts64.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 & (BITS_PER_LONG-1)));
  	n /= BITS_PER_LONG;

  	fdt = files_fdtable(current->files);

  	open_fds = fdt->open_fds + 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 * BITS_PER_LONG;

  	}
  
  	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,
  				unsigned int ll_flag)

  {

  	wait->_key = POLLEX_SET | ll_flag;

  	if (in & bit)
  		wait->_key |= POLLIN_SET;
  	if (out & bit)
  		wait->_key |= POLLOUT_SET;

  }

  int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time)

  {

  	ktime_t expire, *to = NULL;

  	struct poll_wqueues table;
  	poll_table *wait;

  	int retval, i, timed_out = 0;

  	u64 slack = 0;

  	unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;

  	unsigned long busy_end = 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->_qproc = 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;

  		bool can_busy_loop = false;

  		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;

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

  				i += BITS_PER_LONG;

  				continue;
  			}

  			for (j = 0; j < BITS_PER_LONG; ++j, ++i, bit <<= 1) {

  				struct fd f;

  				if (i >= n)
  					break;
  				if (!(bit & all_bits))
  					continue;

  				f = fdget(i);
  				if (f.file) {
  					const struct file_operations *f_op;
  					f_op = f.file->f_op;

  					mask = DEFAULT_POLLMASK;

  					if (f_op->poll) {

  						wait_key_set(wait, in, out,

  							     bit, busy_flag);

  						mask = (*f_op->poll)(f.file, wait);

  					}

  					fdput(f);

  					if ((mask & POLLIN_SET) && (in & bit)) {
  						res_in |= bit;
  						retval++;

  						wait->_qproc = NULL;

  					}
  					if ((mask & POLLOUT_SET) && (out & bit)) {
  						res_out |= bit;
  						retval++;

  						wait->_qproc = NULL;

  					}
  					if ((mask & POLLEX_SET) && (ex & bit)) {
  						res_ex |= bit;
  						retval++;

  						wait->_qproc = NULL;

  					}

  					/* got something, stop busy polling */

  					if (retval) {
  						can_busy_loop = false;
  						busy_flag = 0;
  
  					/*
  					 * only remember a returned
  					 * POLL_BUSY_LOOP if we asked for it
  					 */
  					} else if (busy_flag & mask)
  						can_busy_loop = true;

  				}

  			}
  			if (res_in)
  				*rinp = res_in;
  			if (res_out)
  				*routp = res_out;
  			if (res_ex)
  				*rexp = res_ex;

  			cond_resched();

  		}

  		wait->_qproc = NULL;

  		if (retval || timed_out || signal_pending(current))

  			break;

  		if (table.error) {

  			retval = table.error;
  			break;
  		}

  		/* only if found POLL_BUSY_LOOP sockets && not out of time */

  		if (can_busy_loop && !need_resched()) {
  			if (!busy_end) {
  				busy_end = busy_loop_end_time();
  				continue;
  			}
  			if (!busy_loop_timeout(busy_end))
  				continue;
  		}
  		busy_flag = 0;

  		/*
  		 * 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 = timespec64_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 timespec64 *end_time)

  {
  	fd_set_bits fds;

  	void *bits;

  	int ret, max_fds;

  	size_t size, alloc_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;

  		if (size > (SIZE_MAX / 6))
  			goto out_nofds;
  
  		alloc_size = 6 * size;
  		bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN);
  		if (!bits && alloc_size > PAGE_SIZE)
  			bits = vmalloc(alloc_size);

  		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)

  		kvfree(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 timespec64 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;
  }

  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;
  	struct timespec64 ts64, end_time, *to = NULL;

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

  		ts64 = timespec_to_timespec64(ts);

  		to = &end_time;

  		if (poll_select_set_timeout(to, ts64.tv_sec, ts64.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);

  }

  #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 pwait->_qproc is non-NULL.

   */

  static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait,

  				     bool *can_busy_poll,
  				     unsigned int busy_flag)

  {

  	unsigned int mask;
  	int fd;
  
  	mask = 0;
  	fd = pollfd->fd;
  	if (fd >= 0) {

  		struct fd f = fdget(fd);

  		mask = POLLNVAL;

  		if (f.file) {

  			mask = DEFAULT_POLLMASK;

  			if (f.file->f_op->poll) {

  				pwait->_key = pollfd->events|POLLERR|POLLHUP;

  				pwait->_key |= busy_flag;

  				mask = f.file->f_op->poll(f.file, pwait);

  				if (mask & busy_flag)
  					*can_busy_poll = true;

  			}

  			/* Mask out unneeded events. */
  			mask &= pollfd->events | POLLERR | POLLHUP;

  			fdput(f);

  		}

  	}

  	pollfd->revents = mask;
  
  	return mask;

  }

  static int do_poll(struct poll_list *list, struct poll_wqueues *wait,

  		   struct timespec64 *end_time)

  {

  	poll_table* pt = &wait->pt;

  	ktime_t expire, *to = NULL;
  	int timed_out = 0, count = 0;

  	u64 slack = 0;

  	unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;

  	unsigned long busy_end = 0;

  	/* Optimise the no-wait case */

  	if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {

  		pt->_qproc = NULL;

  		timed_out = 1;
  	}

  	if (end_time && !timed_out)

  		slack = select_estimate_accuracy(end_time);

  	for (;;) {
  		struct poll_list *walk;

  		bool can_busy_loop = false;

  		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 poll_table->_qproc, 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, &can_busy_loop,
  					      busy_flag)) {

  					count++;

  					pt->_qproc = NULL;

  					/* found something, stop busy polling */
  					busy_flag = 0;
  					can_busy_loop = false;

  				}
  			}

  		}

  		/*
  		 * All waiters have already been registered, so don't provide

  		 * a poll_table->_qproc to them on the next loop iteration.

  		 */

  		pt->_qproc = NULL;

  		if (!count) {
  			count = wait->error;
  			if (signal_pending(current))
  				count = -EINTR;
  		}

  		if (count || timed_out)

  			break;

  		/* only if found POLL_BUSY_LOOP sockets && not out of time */

  		if (can_busy_loop && !need_resched()) {
  			if (!busy_end) {
  				busy_end = busy_loop_end_time();
  				continue;
  			}
  			if (!busy_loop_timeout(busy_end))
  				continue;
  		}
  		busy_flag = 0;

  		/*
  		 * 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 = timespec64_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 timespec64 *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(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 timespec64 *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,

  		int, timeout_msecs)

  {

  	struct timespec64 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->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;

  }

  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;
  	struct timespec64 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;
  }