text
stringlengths 0
234
|
|---|
.br read (2) |
fails with the error |
.b einval |
if the size of the supplied buffer is less than 8 bytes. |
.ip |
if the associated clock is either |
.br clock_realtime |
or |
.br clock_realtime_alarm , |
the timer is absolute |
.rb ( tfd_timer_abstime ), |
and the flag |
.br tfd_timer_cancel_on_set |
was specified when calling |
.br timerfd_settime (), |
then |
.br read (2) |
fails with the error |
.br ecanceled |
if the real-time clock undergoes a discontinuous change. |
(this allows the reading application to discover |
such discontinuous changes to the clock.) |
.ip |
if the associated clock is either |
.br clock_realtime |
or |
.br clock_realtime_alarm , |
the timer is absolute |
.rb ( tfd_timer_abstime ), |
and the flag |
.br tfd_timer_cancel_on_set |
was |
.i not |
specified when calling |
.br timerfd_settime (), |
then a discontinuous negative change to the clock (e.g., |
.br clock_settime (2)) |
may cause |
.br read (2) |
to unblock, but return a value of 0 (i.e., no bytes read), |
if the clock change occurs after the time expired, |
but before the |
.br read (2) |
on the file descriptor. |
.tp |
.br poll "(2), " select "(2) (and similar)" |
the file descriptor is readable |
(the |
.br select (2) |
.i readfds |
argument; the |
.br poll (2) |
.b pollin |
flag) |
if one or more timer expirations have occurred. |
.ip |
the file descriptor also supports the other file-descriptor |
multiplexing apis: |
.br pselect (2), |
.br ppoll (2), |
and |
.br epoll (7). |
.tp |
.br ioctl (2) |
the following timerfd-specific command is supported: |
.rs |
.tp |
.br tfd_ioc_set_ticks " (since linux 3.17)" |
.\" commit 5442e9fbd7c23172a1c9bc736629cd123a9923f0 |
adjust the number of timer expirations that have occurred. |
the argument is a pointer to a nonzero 8-byte integer |
.ri ( uint64_t *) |
containing the new number of expirations. |
once the number is set, any waiter on the timer is woken up. |
the only purpose of this command is to restore the expirations |
for the purpose of checkpoint/restore. |
this operation is available only if the kernel was configured with the |
.br config_checkpoint_restore |
option. |
.re |
.tp |
.br close (2) |
when the file descriptor is no longer required it should be closed. |
when all file descriptors associated with the same timer object |
have been closed, |
the timer is disarmed and its resources are freed by the kernel. |
.\" |
.ss fork(2) semantics |
after a |
.br fork (2), |
the child inherits a copy of the file descriptor created by |
.br timerfd_create (). |
the file descriptor refers to the same underlying |
timer object as the corresponding file descriptor in the parent, |
and |
.br read (2)s |
in the child will return information about |
expirations of the timer. |
.\" |
.ss execve(2) semantics |