svcadm(1M)을 검색하려면 섹션에서 1M 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
aio(4)
AIO(4) BSD Kernel Interfaces Manual AIO(4)
NAME
aio — asynchronous I/O
DESCRIPTION
The aio facility provides system calls for asynchronous I/O. Asynchro‐
nous I/O operations are not completed synchronously by the calling
thread. Instead, the calling thread invokes one system call to request
an asynchronous I/O operation. The status of a completed request is
retrieved later via a separate system call.
Asynchronous I/O operations on some file descriptor types may block an
AIO daemon indefinitely resulting in process and/or system hangs. Opera‐
tions on these file descriptor types are considered “unsafe” and disabled
by default. They can be enabled by setting the vfs.aio.enable_unsafe
sysctl node to a non-zero value.
Asynchronous I/O operations on sockets, raw disk devices, and regular
files on local filesystems do not block indefinitely and are always
enabled.
The aio facility uses kernel processes (also known as AIO daemons) to
service most asynchronous I/O requests. These processes are grouped into
pools containing a variable number of processes. Each pool will add or
remove processes to the pool based on load. Pools can be configured by
sysctl nodes that define the minimum and maximum number of processes as
well as the amount of time an idle process will wait before exiting.
One pool of AIO daemons is used to service asynchronous I/O requests for
sockets. These processes are named “soaiod<N>”. The following sysctl
nodes are used with this pool:
kern.ipc.aio.num_procs
The current number of processes in the pool.
kern.ipc.aio.target_procs
The minimum number of processes that should be present in the
pool.
kern.ipc.aio.max_procs
The maximum number of processes permitted in the pool.
kern.ipc.aio.lifetime
The amount of time a process is permitted to idle in clock ticks.
If a process is idle for this amount of time and there are more
processes in the pool than the target minimum, the process will
exit.
A second pool of AIO daemons is used to service all other asynchronous
I/O requests except for I/O requests to raw disks. These processes are
named “aiod<N>”. The following sysctl nodes are used with this pool:
vfs.aio.num_aio_procs
The current number of processes in the pool.
vfs.aio.target_aio_procs
The minimum number of processes that should be present in the
pool.
vfs.aio.max_aio_procs
The maximum number of processes permitted in the pool.
vfs.aio.aiod_lifetime
The amount of time a process is permitted to idle in clock ticks.
If a process is idle for this amount of time and there are more
processes in the pool than the target minimum, the process will
exit.
Asynchronous I/O requests for raw disks are queued directly to the disk
device layer after temporarily wiring the user pages associated with the
request. These requests are not serviced by any of the AIO daemon pools.
Several limits on the number of asynchronous I/O requests are imposed
both system-wide and per-process. These limits are configured via the
following sysctls:
vfs.aio.max_buf_aio
The maximum number of queued asynchronous I/O requests for raw
disks permitted for a single process. Asynchronous I/O requests
that have completed but whose status has not been retrieved via
aio_return(2) or aio_waitcomplete(2) are not counted against this
limit.
vfs.aio.num_buf_aio
The number of queued asynchronous I/O requests for raw disks sys‐
tem-wide.
vfs.aio.max_aio_queue_per_proc
The maximum number of asynchronous I/O requests for a single
process serviced concurrently by the default AIO daemon pool.
vfs.aio.max_aio_per_proc
The maximum number of outstanding asynchronous I/O requests per‐
mitted for a single process. This includes requests that have
not been serviced, requests currently being serviced, and
requests that have completed but whose status has not been
retrieved via aio_return(2) or aio_waitcomplete(2).
vfs.aio.num_queue_count
The number of outstanding asynchronous I/O requests system-wide.
vfs.aio.max_aio_queue
The maximum number of outstanding asynchronous I/O requests per‐
mitted system-wide.
Asynchronous I/O control buffers should be zeroed before initializing
individual fields. This ensures all fields are initialized.
All asynchronous I/O control buffers contain a sigevent structure in the
aio_sigevent field which can be used to request notification when an
operation completes.
For SIGEV_KEVENT notifications, the sigevent s sigev_notify_kqueue field
should contain the descriptor of the kqueue that the event should be
attached to, its sigev_notify_kevent_flags field may contain EV_ONESHOT,
EV_CLEAR, and/or EV_DISPATCH, and its sigev_notify field should be set to
SIGEV_KEVENT. The posted kevent will contain:
Member Value
ident asynchronous I/O control buffer pointer
filter EVFILT_AIO
flags EV_EOF
udata value stored in aio_sigevent.sigev_value
For SIGEV_SIGNO and SIGEV_THREAD_ID notifications, the information for
the queued signal will include SI_ASYNCIO in the si_code field and the
value stored in sigevent.sigev_value in the si_value field.
For SIGEV_THREAD notifications, the value stored in
aio_sigevent.sigev_value is passed to the
aio_sigevent.sigev_notify_function as described in sigevent(3).
SEE ALSO
aio_cancel(2), aio_error(2), aio_read(2), aio_return(2), aio_suspend(2),
aio_waitcomplete(2), aio_write(2), lio_listio(2), sigevent(3), sysctl(8)
HISTORY
The aio facility appeared as a kernel option in FreeBSD 3.0. The aio
kernel module appeared in FreeBSD 5.0. The aio facility was integrated
into all kernels in FreeBSD 11.0.
BSD June 22, 2017 BSD