NAME
epollctl - control interface for an epoll descriptor SYNOPSIS
#include
int epollctl(int epfd, int op, int fd, struct epollevent *event); DESCRIPTION This system call performs control operations on the epoll(7) instance referred to by the file descriptor epfd. It requests that the opera‐ tion op be performed for the target file descriptor, fd. Valid values for the op argument are : EPOLLCTLADD Register the target file descriptor fd on the epoll instance referred to by the file descriptor epfd and associate the event event with the internal file linked to fd. EPOLLCTLMOD Change the event event associated with the target file descrip‐ tor fd. EPOLLCTLDEL Remove (deregister) the target file descriptor fd from the epoll instance referred to by epfd. The event is ignored and can be NULL (but see BUGS below). The event argument describes the object linked to the file descriptor fd. The struct epollevent is defined as : typedef union epolldata { void *ptr; int fd; uint32t u32; uint64t u64; } epolldatat; struct epollevent { uint32t events; /* Epoll events */ epolldatat data; /* User data variable */ }; The events member is a bit set composed using the following available event types: EPOLLIN The associated file is available for read(2) operations. EPOLLOUT The associated file is available for write(2) operations. EPOLLRDHUP (since Linux 2.6.17) Stream socket peer closed connection, or shut down writing half of connection. (This flag is especially useful for writing sim‐ ple code to detect peer shutdown when using Edge Triggered moni‐ toring.) EPOLLPRI There is urgent data available for read(2) operations. EPOLLERR Error condition happened on the associated file descriptor. epollwait(2) will always wait for this event; it is not neces‐ sary to set it in events. EPOLLHUP Hang up happened on the associated file descriptor. epollwait(2) will always wait for this event; it is not neces‐ sary to set it in events. EPOLLET Sets the Edge Triggered behavior for the associated file descriptor. The default behavior for epoll is Level Triggered. See epoll(7) for more detailed information about Edge and Level Triggered event distribution architectures. EPOLLONESHOT (since Linux 2.6.2) Sets the one-shot behavior for the associated file descriptor. This means that after an event is pulled out with epollwait(2) the associated file descriptor is internally disabled and no other events will be reported by the epoll interface. The user must call epollctl() with EPOLLCTLMOD to rearm the file descriptor with a new event mask. RETURN VALUE When successful, epollctl() returns zero. When an error occurs,
epollctl() returns -1 and errno is set appropriately. ERRORS EBADF epfd or fd is not a valid file descriptor. EEXIST op was EPOLLCTLADD, and the supplied file descriptor fd is already registered with this epoll instance. EINVAL epfd is not an epoll file descriptor, or fd is the same as epfd, or the requested operation op is not supported by this inter‐ face. ENOENT op was EPOLLCTLMOD or EPOLLCTLDEL, and fd is not registered with this epoll instance. ENOMEM There was insufficient memory to handle the requested op control operation. ENOSPC The limit imposed by /proc/sys/fs/epoll/maxuserwatches was encountered while trying to register (EPOLLCTLADD) a new file descriptor on an epoll instance. See epoll(7) for further details. EPERM The target file fd does not support epoll. VERSIONS epollctl() was added to the kernel in version 2.6. CONFORMING TO
epollctl() is Linux-specific. Library support is provided in glibc starting with version 2.3.2. NOTES The epoll interface supports all file descriptors that support poll(2). BUGS In kernel versions before 2.6.9, the EPOLLCTLDEL operation required a
non-NULL pointer in event, even though this argument is ignored. Since Linux 2.6.9, event can be specified as NULL when using EPOLLCTLDEL. Applications that need to be portable to kernels before 2.6.9 should
specify a non-NULL pointer in event. SEE ALSO epollcreate(2), epollwait(2), poll(2), epoll(7) COLOPHON
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Linux 2012-04-15 EPOLLCTL(2)