Quelle select.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
* 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/compat.h>
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/sched/rt.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/freezer.h>
#include <net/busy_poll.h>
#include <linux/vmalloc.h>

#include <linux/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;
u64 slack = current->timer_slack_ns;

if (slack == 0)
  return 0;

ktime_get_ts64(&now);
now = timespec64_sub(*tv, now);
ret = __estimate_accuracy(&now);
if (ret < slack)
  return slack;
return ret;
}

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

#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_entry_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();
WRITE_ONCE(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_entry_t *wait, unsigned mode, int sync, void *key)
{
struct poll_table_entry *entry;

entry = container_of(wait, struct poll_table_entry, wait);
if (key && !(key_to_poll(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);
}

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

set_current_state(state);
if (!READ_ONCE(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;
}

/**
* 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;
}

enum poll_time_type {
PT_TIMEVAL = 0,
PT_OLD_TIMEVAL = 1,
PT_TIMESPEC = 2,
PT_OLD_TIMESPEC = 3,
};

static int poll_select_finish(struct timespec64 *end_time,
         void __user *p,
         enum poll_time_type pt_type, int ret)
{
struct timespec64 rts;

restore_saved_sigmask_unless(ret == -ERESTARTNOHAND);

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

switch (pt_type) {
case PT_TIMEVAL:
  {
   struct __kernel_old_timeval rtv;

   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;
  }
  break;
case PT_OLD_TIMEVAL:
  {
   struct old_timeval32 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;
  }
  break;
case PT_TIMESPEC:
  if (!put_timespec64(&rts, p))
   return ret;
  break;
case PT_OLD_TIMESPEC:
  if (!put_old_timespec32(&rts, p))
   return ret;
  break;
default:
  BUG();
}
/*
* 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;
}

/*
* Scalable version of the fd_set.
*/

typedef struct {
unsigned long *in, *out, *ex;
unsigned long *res_in, *res_out, *res_ex;
} fd_set_bits;

/*
* How many longwords for "nr" bits?
*/
#define FDS_BITPERLONG (8*sizeof(long))
#define FDS_LONGS(nr) (((nr)+FDS_BITPERLONG-1)/FDS_BITPERLONG)
#define FDS_BYTES(nr) (FDS_LONGS(nr)*sizeof(long))

/*
* Use "unsigned long" accesses to let user-mode fd_set's be long-aligned.
*/
static inline
int get_fd_set(unsigned long nr, void __user *ufdset, unsigned long *fdset)
{
nr = FDS_BYTES(nr);
if (ufdset)
  return copy_from_user(fdset, ufdset, nr) ? -EFAULT : 0;

memset(fdset, 0, nr);
return 0;
}

static inline unsigned long __must_check
set_fd_set(unsigned long nr, void __user *ufdset, unsigned long *fdset)
{
if (ufdset)
  return __copy_to_user(ufdset, fdset, FDS_BYTES(nr));
return 0;
}

static inline
void zero_fd_set(unsigned long nr, unsigned long *fdset)
{
memset(fdset, 0, FDS_BYTES(nr));
}

#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 (EPOLLRDNORM | EPOLLRDBAND | EPOLLIN | EPOLLHUP | EPOLLERR |\
   EPOLLNVAL)
#define POLLOUT_SET (EPOLLWRBAND | EPOLLWRNORM | EPOLLOUT | EPOLLERR |\
    EPOLLNVAL)
#define POLLEX_SET (EPOLLPRI | EPOLLNVAL)

static inline __poll_t select_poll_one(int fd, poll_table *wait, unsigned long in,
    unsigned long out, unsigned long bit,
    __poll_t ll_flag)
{
CLASS(fd, f)(fd);

if (fd_empty(f))
  return EPOLLNVAL;

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

return vfs_poll(fd_file(f), wait);
}

static noinline_for_stack 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;
__poll_t busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
unsigned long busy_start = 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, j;
   unsigned long res_in = 0, res_out = 0, res_ex = 0;
   __poll_t mask;

   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) {
    if (i >= n)
     break;
    if (!(bit & all_bits))
     continue;
    mask = select_poll_one(i, wait, in, out, bit,
             busy_flag);
    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_start) {
    busy_start = busy_loop_current_time();
    continue;
   }
   if (!busy_loop_timeout(busy_start))
    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 (unlikely(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 = kvmalloc(alloc_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)
  kvfree(bits);
out_nofds:
return ret;
}

static int kern_select(int n, fd_set __user *inp, fd_set __user *outp,
         fd_set __user *exp, struct __kernel_old_timeval __user *tvp)
{
struct timespec64 end_time, *to = NULL;
struct __kernel_old_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);
return poll_select_finish(&end_time, tvp, PT_TIMEVAL, ret);
}

SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
  fd_set __user *, exp, struct __kernel_old_timeval __user *, tvp)
{
return kern_select(n, inp, outp, exp, tvp);
}

static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
         fd_set __user *exp, void __user *tsp,
         const sigset_t __user *sigmask, size_t sigsetsize,
         enum poll_time_type type)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  switch (type) {
  case PT_TIMESPEC:
   if (get_timespec64(&ts, tsp))
    return -EFAULT;
   break;
  case PT_OLD_TIMESPEC:
   if (get_old_timespec32(&ts, tsp))
    return -EFAULT;
   break;
  default:
   BUG();
  }

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

ret = set_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = core_sys_select(n, inp, outp, exp, to);
return poll_select_finish(&end_time, tsp, type, 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.
*/
struct sigset_argpack {
sigset_t __user *p;
size_t size;
};

static inline int get_sigset_argpack(struct sigset_argpack *to,
         struct sigset_argpack __user *from)
{
// the path is hot enough for overhead of copy_from_user() to matter
if (from) {
  if (can_do_masked_user_access())
   from = masked_user_access_begin(from);
  else if (!user_read_access_begin(from, sizeof(*from)))
   return -EFAULT;
  unsafe_get_user(to->p, &from->p, Efault);
  unsafe_get_user(to->size, &from->size, Efault);
  user_read_access_end();
}
return 0;
Efault:
user_read_access_end();
return -EFAULT;
}

SYSCALL_DEFINE6(pselect6, int, n, fd_set __user *, inp, fd_set __user *, outp,
  fd_set __user *, exp, struct __kernel_timespec __user *, tsp,
  void __user *, sig)
{
struct sigset_argpack x = {NULL, 0};

if (get_sigset_argpack(&x, sig))
  return -EFAULT;

return do_pselect(n, inp, outp, exp, tsp, x.p, x.size, PT_TIMESPEC);
}

#if defined(CONFIG_COMPAT_32BIT_TIME) && !defined(CONFIG_64BIT)

SYSCALL_DEFINE6(pselect6_time32, int, n, fd_set __user *, inp, fd_set __user *, outp,
  fd_set __user *, exp, struct old_timespec32 __user *, tsp,
  void __user *, sig)
{
struct sigset_argpack x = {NULL, 0};

if (get_sigset_argpack(&x, sig))
  return -EFAULT;

return do_pselect(n, inp, outp, exp, tsp, x.p, x.size, PT_OLD_TIMESPEC);
}

#endif

#ifdef __ARCH_WANT_SYS_OLD_SELECT
struct sel_arg_struct {
unsigned long n;
fd_set __user *inp, *outp, *exp;
struct __kernel_old_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 kern_select(a.n, a.inp, a.outp, a.exp, a.tvp);
}
#endif

struct poll_list {
struct poll_list *next;
unsigned int len;
struct pollfd entries[] __counted_by(len);
};

#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 __poll_t do_pollfd(struct pollfd *pollfd, poll_table *pwait,
         bool *can_busy_poll,
         __poll_t busy_flag)
{
int fd = pollfd->fd;
__poll_t mask, filter;

if (unlikely(fd < 0))
  return 0;

CLASS(fd, f)(fd);
if (fd_empty(f))
  return EPOLLNVAL;

/* userland u16 ->events contains POLL... bitmap */
filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
pwait->_key = filter | busy_flag;
mask = vfs_poll(fd_file(f), pwait);
if (mask & busy_flag)
  *can_busy_poll = true;
return mask & filter;  /* Mask out unneeded events. */
}

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;
__poll_t busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
unsigned long busy_start = 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++) {
    __poll_t mask;
    /*
* 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.
*/
    mask = do_pollfd(pfd, pt, &can_busy_loop, busy_flag);
    pfd->revents = mangle_poll(mask);
    if (mask) {
     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 = -ERESTARTNOHAND;
  }
  if (count || timed_out)
   break;

  /* only if found POLL_BUSY_LOOP sockets && not out of time */
  if (can_busy_loop && !need_resched()) {
   if (!busy_start) {
    busy_start = busy_loop_current_time();
    continue;
   }
   if (!busy_loop_timeout(busy_start))
    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))

static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
  struct timespec64 *end_time)
{
struct poll_wqueues table;
int err = -EFAULT, fdcount;
/* 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 int todo = nfds;
unsigned int len;

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;

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

  len = min(todo, POLLFD_PER_PAGE);
  walk = walk->next = kmalloc(struct_size(walk, entries, len),
         GFP_KERNEL);
  if (!walk) {
   err = -ENOMEM;
   goto out_fds;
  }
}

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

if (!user_write_access_begin(ufds, nfds * sizeof(*ufds)))
  goto out_fds;

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

  for (j = walk->len; j; fds++, ufds++, j--)
   unsafe_put_user(fds->revents, &ufds->revents, Efault);
   }
user_write_access_end();

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

return err;

Efault:
user_write_access_end();
err = -EFAULT;
goto out_fds;
}

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 == -ERESTARTNOHAND)
  ret = set_restart_fn(restart_block, do_restart_poll);

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 == -ERESTARTNOHAND) {
  struct restart_block *restart_block;

  restart_block = ¤t->restart_block;
  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 = set_restart_fn(restart_block, do_restart_poll);
}
return ret;
}

SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
  struct __kernel_timespec __user *, tsp, const sigset_t __user *, sigmask,
  size_t, sigsetsize)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  if (get_timespec64(&ts, tsp))
   return -EFAULT;

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

ret = set_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = do_sys_poll(ufds, nfds, to);
return poll_select_finish(&end_time, tsp, PT_TIMESPEC, ret);
}

#if defined(CONFIG_COMPAT_32BIT_TIME) && !defined(CONFIG_64BIT)

SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds, unsigned int, nfds,
  struct old_timespec32 __user *, tsp, const sigset_t __user *, sigmask,
  size_t, sigsetsize)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  if (get_old_timespec32(&ts, tsp))
   return -EFAULT;

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

ret = set_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = do_sys_poll(ufds, nfds, to);
return poll_select_finish(&end_time, tsp, PT_OLD_TIMESPEC, ret);
}
#endif

#ifdef CONFIG_COMPAT
#define __COMPAT_NFDBITS       (8 * sizeof(compat_ulong_t))

/*
* Ooo, nasty.  We need here to frob 32-bit unsigned longs to
* 64-bit unsigned longs.
*/
static
int compat_get_fd_set(unsigned long nr, compat_ulong_t __user *ufdset,
   unsigned long *fdset)
{
if (ufdset) {
  return compat_get_bitmap(fdset, ufdset, nr);
} else {
  zero_fd_set(nr, fdset);
  return 0;
}
}

static
int compat_set_fd_set(unsigned long nr, compat_ulong_t __user *ufdset,
        unsigned long *fdset)
{
if (!ufdset)
  return 0;
return compat_put_bitmap(ufdset, fdset, nr);
}

/*
* This is a virtual copy of sys_select from fs/select.c and probably
* should be compared to it from time to time
*/

/*
* 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.
*/
static int compat_core_sys_select(int n, compat_ulong_t __user *inp,
compat_ulong_t __user *outp, compat_ulong_t __user *exp,
struct timespec64 *end_time)
{
fd_set_bits fds;
void *bits;
int size, max_fds, ret = -EINVAL;
struct fdtable *fdt;
long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];

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) {
  bits = kmalloc_array(6, size, GFP_KERNEL);
  ret = -ENOMEM;
  if (!bits)
   goto out_nofds;
}
fds.in      = (unsigned long *)  bits;
fds.out     = (unsigned long *) (bits +   size);
fds.ex      = (unsigned long *) (bits + 2*size);
fds.res_in  = (unsigned long *) (bits + 3*size);
fds.res_out = (unsigned long *) (bits + 4*size);
fds.res_ex  = (unsigned long *) (bits + 5*size);

if ((ret = compat_get_fd_set(n, inp, fds.in)) ||
     (ret = compat_get_fd_set(n, outp, fds.out)) ||
     (ret = compat_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 (compat_set_fd_set(n, inp, fds.res_in) ||
     compat_set_fd_set(n, outp, fds.res_out) ||
     compat_set_fd_set(n, exp, fds.res_ex))
  ret = -EFAULT;
out:
if (bits != stack_fds)
  kfree(bits);
out_nofds:
return ret;
}

static int do_compat_select(int n, compat_ulong_t __user *inp,
compat_ulong_t __user *outp, compat_ulong_t __user *exp,
struct old_timeval32 __user *tvp)
{
struct timespec64 end_time, *to = NULL;
struct old_timeval32 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 = compat_core_sys_select(n, inp, outp, exp, to);
return poll_select_finish(&end_time, tvp, PT_OLD_TIMEVAL, ret);
}

COMPAT_SYSCALL_DEFINE5(select, int, n, compat_ulong_t __user *, inp,
compat_ulong_t __user *, outp, compat_ulong_t __user *, exp,
struct old_timeval32 __user *, tvp)
{
return do_compat_select(n, inp, outp, exp, tvp);
}

struct compat_sel_arg_struct {
compat_ulong_t n;
compat_uptr_t inp;
compat_uptr_t outp;
compat_uptr_t exp;
compat_uptr_t tvp;
};

COMPAT_SYSCALL_DEFINE1(old_select, struct compat_sel_arg_struct __user *, arg)
{
struct compat_sel_arg_struct a;

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

static long do_compat_pselect(int n, compat_ulong_t __user *inp,
compat_ulong_t __user *outp, compat_ulong_t __user *exp,
void __user *tsp, compat_sigset_t __user *sigmask,
compat_size_t sigsetsize, enum poll_time_type type)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  switch (type) {
  case PT_OLD_TIMESPEC:
   if (get_old_timespec32(&ts, tsp))
    return -EFAULT;
   break;
  case PT_TIMESPEC:
   if (get_timespec64(&ts, tsp))
    return -EFAULT;
   break;
  default:
   BUG();
  }

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

ret = set_compat_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = compat_core_sys_select(n, inp, outp, exp, to);
return poll_select_finish(&end_time, tsp, type, ret);
}

struct compat_sigset_argpack {
compat_uptr_t p;
compat_size_t size;
};
static inline int get_compat_sigset_argpack(struct compat_sigset_argpack *to,
         struct compat_sigset_argpack __user *from)
{
if (from) {
  if (!user_read_access_begin(from, sizeof(*from)))
   return -EFAULT;
  unsafe_get_user(to->p, &from->p, Efault);
  unsafe_get_user(to->size, &from->size, Efault);
  user_read_access_end();
}
return 0;
Efault:
user_read_access_end();
return -EFAULT;
}

COMPAT_SYSCALL_DEFINE6(pselect6_time64, int, n, compat_ulong_t __user *, inp,
compat_ulong_t __user *, outp, compat_ulong_t __user *, exp,
struct __kernel_timespec __user *, tsp, void __user *, sig)
{
struct compat_sigset_argpack x = {0, 0};

if (get_compat_sigset_argpack(&x, sig))
  return -EFAULT;

return do_compat_pselect(n, inp, outp, exp, tsp, compat_ptr(x.p),
     x.size, PT_TIMESPEC);
}

#if defined(CONFIG_COMPAT_32BIT_TIME)

COMPAT_SYSCALL_DEFINE6(pselect6_time32, int, n, compat_ulong_t __user *, inp,
compat_ulong_t __user *, outp, compat_ulong_t __user *, exp,
struct old_timespec32 __user *, tsp, void __user *, sig)
{
struct compat_sigset_argpack x = {0, 0};

if (get_compat_sigset_argpack(&x, sig))
  return -EFAULT;

return do_compat_pselect(n, inp, outp, exp, tsp, compat_ptr(x.p),
     x.size, PT_OLD_TIMESPEC);
}

#endif

#if defined(CONFIG_COMPAT_32BIT_TIME)
COMPAT_SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds,
unsigned int,  nfds, struct old_timespec32 __user *, tsp,
const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  if (get_old_timespec32(&ts, tsp))
   return -EFAULT;

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

ret = set_compat_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = do_sys_poll(ufds, nfds, to);
return poll_select_finish(&end_time, tsp, PT_OLD_TIMESPEC, ret);
}
#endif

/* New compat syscall for 64 bit time_t*/
COMPAT_SYSCALL_DEFINE5(ppoll_time64, struct pollfd __user *, ufds,
unsigned int,  nfds, struct __kernel_timespec __user *, tsp,
const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize)
{
struct timespec64 ts, end_time, *to = NULL;
int ret;

if (tsp) {
  if (get_timespec64(&ts, tsp))
   return -EFAULT;

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

ret = set_compat_user_sigmask(sigmask, sigsetsize);
if (ret)
  return ret;

ret = do_sys_poll(ufds, nfds, to);
return poll_select_finish(&end_time, tsp, PT_TIMESPEC, ret);
}

#endif

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