FreeBSD/Linux Kernel Cross Reference
sys/fs/select.c

     /*
      * 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 <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;
           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 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 & (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)
   {
           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->_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;
   
                   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 && f_op->poll) {
                                                   wait_key_set(wait, in, out, bit);
                                                   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;
                                           }
                                   }
                           }
                           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;
                   }
   
                   /*
                    * 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;
   }
   
   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);
   }
   
   #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)
   {
           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 && f.file->f_op->poll) {
                                   pwait->_key = pollfd->events|POLLERR|POLLHUP;
                                   mask = f.file->f_op->poll(f.file, pwait);
                           }
                           /* Mask out unneeded events. */
                           mask &= pollfd->events | POLLERR | POLLHUP;
                           fdput(f);
                   }
           }
           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->_qproc = 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 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)) {
                                           count++;
                                           pt->_qproc = NULL;
                                   }
                           }
                   }
                   /*
                    * 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;
   
                   /*
                    * 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,
                   int, 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;
   }
   
   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;
   }

Cache object: 8718bc1d3dbe471bc425f73bfea98073