NAME

       epoll_create, epoll_create1 - open an epoll file descriptor

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/epoll.h>

       int epoll_create(int size);
       int epoll_create1(int flags);

DESCRIPTION

       epoll_create()  creates  a  new  epoll(7) instance.  Since Linux 2.6.8, the size argument is ignored, but
       must be greater than zero; see HISTORY.

       epoll_create() returns a file descriptor referring to the new epoll instance.  This  file  descriptor  is
       used  for  all the subsequent calls to the epoll interface.  When no longer required, the file descriptor
       returned by epoll_create() should be closed by using close(2).  When all file descriptors referring to an
       epoll  instance  have been closed, the kernel destroys the instance and releases the associated resources
       for reuse.

   epoll_create1()
       If flags is 0, then, other than the fact that the obsolete size argument is dropped,  epoll_create1()  is
       the same as epoll_create().  The following value can be included in flags to obtain different behavior:

       EPOLL_CLOEXEC
              Set  the  close-on-exec  (FD_CLOEXEC) flag on the new file descriptor.  See the description of the
              O_CLOEXEC flag in open(2) for reasons why this may be useful.

RETURN VALUE

       On success, these system calls return a file  descriptor  (a  nonnegative  integer).   On  error,  -1  is
       returned, and errno is set to indicate the error.

ERRORS

       EINVAL size is not positive.

       EINVAL (epoll_create1()) Invalid value specified in flags.

       EMFILE The per-process limit on the number of open file descriptors has been reached.

       ENFILE The system-wide limit on the total number of open files has been reached.

       ENOMEM There was insufficient memory to create the kernel object.

STANDARDS

       Linux.

HISTORY

       epoll_create()
              Linux 2.6, glibc 2.3.2.

       epoll_create1()
              Linux 2.6.27, glibc 2.9.

       In the initial epoll_create() implementation, the size argument informed the kernel of the number of file
       descriptors that the caller expected to add to the epoll instance.  The kernel used this information as a
       hint  for  the  amount of space to initially allocate in internal data structures describing events.  (If
       necessary, the kernel would allocate more space if the caller's usage exceeded the hint given  in  size.)
       Nowadays,  this  hint  is  no  longer required (the kernel dynamically sizes the required data structures
       without needing the hint), but size must still  be  greater  than  zero,  in  order  to  ensure  backward
       compatibility when new epoll applications are run on older kernels.

       Prior  to  Linux 2.6.29, a /proc/sys/fs/epoll/max_user_instances kernel parameter limited live epolls for
       each real user ID, and caused epoll_create() to fail with EMFILE on overrun.

SEE ALSO

       close(2), epoll_ctl(2), epoll_wait(2), epoll(7)