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

NAME
       io_getevents - read asynchronous I/O events from the completion queue

SYNOPSIS
       #include <linux/aio_abi.h>    /* Definition of *io_* types */
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_io_getevents, aio_context_t ctx_id,
                   long min_nr, long nr, struct io_event *events,
                   struct timespec *timeout);

       Note: glibc provides no wrapper for io_getevents(), necessitating the use of syscall(2).

DESCRIPTION
       Note:  this  page  describes  the  raw  Linux system call interface.  The wrapper function provided by libaio uses a different type for the ctx_id argument.  See
       NOTES.

       The io_getevents() system call attempts to read at least min_nr events and up to nr events from the completion queue of the AIO context specified by ctx_id.

       The timeout argument specifies the amount of time to wait for events, and is specified as a relative timeout in a structure of the following form:

           struct timespec {
               time_t tv_sec;      /* seconds */
               long   tv_nsec;     /* nanoseconds [0 .. 999999999] */
           };

       The specified time will be rounded up to the system clock granularity and is guaranteed not to expire early.

       Specifying timeout as NULL means block indefinitely until at least min_nr events have been obtained.

RETURN VALUE
       On success, io_getevents() returns the number of events read.  This may be 0, or a value less than min_nr, if the timeout expired.  It  may  also  be  a  nonzero
       value less than min_nr, if the call was interrupted by a signal handler.

       For the failure return, see NOTES.

ERRORS
       EFAULT Either events or timeout is an invalid pointer.

       EINTR  Interrupted by a signal handler; see signal(7).

       EINVAL ctx_id is invalid.  min_nr is out of range or nr is out of range.

       ENOSYS io_getevents() is not implemented on this architecture.

VERSIONS
       The asynchronous I/O system calls first appeared in Linux 2.5.

CONFORMING TO
       io_getevents() is Linux-specific and should not be used in programs that are intended to be portable.

NOTES
       You probably want to use the io_getevents() wrapper function provided by libaio.

       Note  that the libaio wrapper function uses a different type (io_context_t) for the ctx_id argument.  Note also that the libaio wrapper does not follow the usual
       C library conventions for indicating errors: on error it returns a negated error number (the negative of one of the values listed in ERRORS).  If the system call
       is  invoked  via syscall(2), then the return value follows the usual conventions for indicating an error: -1, with errno set to a (positive) value that indicates
       the error.

BUGS
       An invalid ctx_id may cause a segmentation fault instead of generating the error EINVAL.

SEE ALSO
       io_cancel(2), io_destroy(2), io_setup(2), io_submit(2), aio(7), time(7)

Linux                                                                          2021-03-22                                                                IO_GETEVENTS(2)