selinit(9) [netbsd man page]

SELECT(9)						   BSD Kernel Developer's Manual						 SELECT(9)

NAME

     seldestroy, selinit, selrecord, selnotify -- select and poll subsystem

SYNOPSIS

     #include <sys/param.h>
     #include <sys/select.h>

     void
     seldestroy(struct selinfo *sip);

     void
     selinit(struct selinfo *sip);

     void
     selrecord(struct lwp *selector, struct selinfo *sip);

     void
     selnotify(struct selinfo *sip, int events, long knhint);

DESCRIPTION

     selinit() and seldestroy() functions must be used to initialize and destroy the struct selinfo.  The seldestroy() function may block.

     selrecord() and selnotify() are used by device drivers to coordinate with the kernel implementation of select(2) and poll(2).  Each object
     that can be polled contains a selinfo record.  Device drivers provide locking for the selinfo record.

     selrecord() records that the calling thread is interested in events related to a given object.  selrecord() should only be called when the
     poll routine determines that the object is not ready for I/O: there are no events of interest pending.  The check for pending I/O and call to
     selrecord() must be atomic.  Atomicity can be provided by holding the object's lock across the test and call to selrecord().  For non-MPSAFE
     drivers, the global kernel_lock is enough to provide atomicity.

     selnotify() is called by the underlying object handling code in order to notify any waiting threads that an event of interest has occurred.
     The same lock held across the poll method and call to selrecord() must be held across the call to selnotify().  The lock prevents an event of
     interest being signalled while a thread is in the process of recording its interest.

     The events indicates which event happen.  Zero may be used if unknown.

     selnotify() also calls KNOTE() passing knhint as an argument.

CODE REFERENCES

     The core of the select and poll subsystem implementation is in sys/kern/sys_select.c.  Data structures and function prototypes are located in
     sys/sys/select.h, sys/sys/poll.h and sys/sys/selinfo.h.

SEE ALSO

     poll(2), select(2), knote(9)

BSD
								   May 13, 2008 							       BSD

POLL(2) 						     Linux Programmer's Manual							   POLL(2)

NAME

       poll - wait for some event on a file descriptor

SYNOPSIS

       #include <sys/poll.h>

       int poll(struct pollfd *ufds, unsigned int nfds, int timeout);

DESCRIPTION

       poll is a variation on the theme of select.  It specifies an array of nfds structures of type
	       struct pollfd {
		       int fd;		 /* file descriptor */
		       short events;	 /* requested events */
		       short revents;	 /* returned events */
	       };
       and  a  timeout	in  milliseconds. A negative value means infinite timeout.  The field fd contains a file descriptor for an open file.  The
       field events is an input parameter, a bitmask specifying the events the application is interested in.   The  field  revents  is	an  output
       parameter,  filled  by  the  kernel with the events that actually occurred, either of the type requested, or of one of the types POLLERR or
       POLLHUP or POLLNVAL.  (These three bits are meaningless in the events field, and will be set in the revents field whenever the  correspond-
       ing  condition is true.)  If none of the events requested (and no error) has occurred for any of the file descriptors, the kernel waits for
       timeout milliseconds for one of these events to occur.  The following possible bits in these masks are defined in <sys/poll.h>
	   #define POLLIN      0x0001	 /* There is data to read */
	   #define POLLPRI     0x0002	 /* There is urgent data to read */
	   #define POLLOUT     0x0004	 /* Writing now will not block */
	   #define POLLERR     0x0008	 /* Error condition */
	   #define POLLHUP     0x0010	 /* Hung up */
	   #define POLLNVAL    0x0020	 /* Invalid request: fd not open */
       In <asm/poll.h> also the values POLLRDNORM, POLLRDBAND, POLLWRNORM, POLLWRBAND and POLLMSG are defined.

RETURN VALUE

       On success, a positive number is returned, where the number returned is the number of structures which have  non-zero  revents  fields  (in
       other  words,  those  descriptors  with events or errors reported).  A value of 0 indicates that the call timed out and no file descriptors
       have been selected. On error, -1 is returned, and errno is set appropriately.

ERRORS

       EBADF  An invalid file descriptor was given in one of the sets.

       ENOMEM There was no space to allocate file descriptor tables.

       EFAULT The array given as argument was not contained in the calling program's address space.

       EINTR  A signal occurred before any requested event.

CONFORMING TO

       XPG4-UNIX.

AVAILABILITY

       The poll() systemcall was introduced in Linux 2.1.23.  The poll() library call was introduced in libc 5.4.28 (and provides emulation  using
       select if your kernel does not have a poll syscall).

SEE ALSO

       select(2), select_tut(2)

Linux 2.1.23							    1997-12-07								   POLL(2)