4092a25cd0
- Avoid double use of "request" in a single sentence. Instead, describe aio_sigevent as being used to request notification of the associated operation's completion. This matches the language used to describe aio_sigevent in aio(4). - Simplify the prohibition on modifying buffers while requests are in flight. - Fix case mismatch. - Drop note about not using stack variables. C programmers should be able to figure out if a stack variable is safe based on the later warning about the life cycle requirements of control blocks. - Remove prohibition on modifying the I/O buffer for aio_fsync() since it does not use an I/O buffer. For aio_mlock(), prohibit modifications to the mapping (e.g. due to mprotect, munmap, mmap, etc.) but do not prohibit modifications to the memory backing the buffer (stores into the pages backing the buffer). Requested by: wblock (1,2), kib (4) Reviewed by: kib, rpokala, wblock MFC after: 3 days Sponsored by: Chelsio Communications Differential Revision: https://reviews.freebsd.org/D7462
179 lines
4.9 KiB
Groff
179 lines
4.9 KiB
Groff
.\" Copyright (c) 2013 Sergey Kandaurov
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 19, 2016
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.Dt AIO_FSYNC 2
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.Os
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.Sh NAME
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.Nm aio_fsync
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.Nd asynchronous file synchronization (REALTIME)
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In aio.h
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.Ft int
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.Fn aio_fsync "int op" "struct aiocb *iocb"
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.Sh DESCRIPTION
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The
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.Fn aio_fsync
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system call allows the calling process to move all modified data
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associated with the descriptor
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.Fa iocb->aio_fildes
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to a permanent storage device.
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The call returns immediately after the synchronization request has been
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enqueued to the descriptor; the synchronization may or may not have
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completed at the time the call returns.
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.Pp
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The
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.Fa op
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argument can only be set to
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.Dv O_SYNC
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to cause all currently queued I/O operations to be completed
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as if by a call to
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.Xr fsync 2 .
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.Pp
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If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it,
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then the enqueued operation is submitted at a priority equal to that
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of the calling process minus
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.Fa iocb->aio_reqprio .
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.Pp
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The
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.Fa iocb
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pointer may be subsequently used as an argument to
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.Fn aio_return
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and
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.Fn aio_error
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in order to determine return or error status for the enqueued operation
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while it is in progress.
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.Pp
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If the request could not be enqueued (generally due to invalid arguments),
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the call returns without having enqueued the request.
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.Pp
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The
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.Fa iocb->aio_sigevent
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structure can be used to request notification of the operation's
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completion as described in
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.Xr aio 4 .
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.Sh RESTRICTIONS
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The Asynchronous I/O Control Block structure pointed to by
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.Fa iocb
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must remain valid until the
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operation has completed.
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.Pp
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The asynchronous I/O control buffer
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.Fa iocb
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should be zeroed before the
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.Fn aio_fsync
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call to avoid passing bogus context information to the kernel.
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.Pp
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Modification of the Asynchronous I/O Control Block structure is not allowed
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while the request is queued.
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.Sh RETURN VALUES
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.Rv -std aio_fsync
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.Sh ERRORS
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The
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.Fn aio_fsync
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system call will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The request was not queued because of system resource limitations.
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.It Bq Er EINVAL
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er EOPNOTSUPP
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Asynchronous file synchronization operations on the file descriptor
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.Fa iocb->aio_fildes
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are unsafe and unsafe asynchronous I/O operations are disabled.
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.It Bq Er EINVAL
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A value of the
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.Fa op
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argument is not set to
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.Dv O_SYNC .
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.El
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.Pp
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The following conditions may be synchronously detected when the
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.Fn aio_fsync
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system call is made, or asynchronously, at any time thereafter.
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If they are detected at call time,
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.Fn aio_fsync
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returns -1 and sets
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.Va errno
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appropriately; otherwise the
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.Fn aio_return
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system call must be called, and will return -1, and
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.Fn aio_error
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must be called to determine the actual value that would have been
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returned in
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.Va errno .
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa iocb->aio_fildes
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argument
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is not a valid descriptor.
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.It Bq Er EINVAL
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This implementation does not support synchronized I/O for this file.
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.El
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.Pp
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If the request is successfully enqueued, but subsequently cancelled
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or an error occurs, the value returned by the
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.Fn aio_return
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system call is per the
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.Xr read 2
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and
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.Xr write 2
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system calls, and the value returned by the
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.Fn aio_error
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system call is one of the error returns from the
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.Xr read 2
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or
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.Xr write 2
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system calls.
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.Sh SEE ALSO
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.Xr aio_cancel 2 ,
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.Xr aio_error 2 ,
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.Xr aio_read 2 ,
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.Xr aio_return 2 ,
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.Xr aio_suspend 2 ,
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.Xr aio_waitcomplete 2 ,
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.Xr aio_write 2 ,
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.Xr fsync 2 ,
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.Xr sigevent 3 ,
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.Xr siginfo 3 ,
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.Xr aio 4
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.Sh STANDARDS
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The
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.Fn aio_fsync
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system call is expected to conform to the
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.St -p1003.1
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standard.
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.Sh HISTORY
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The
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.Fn aio_fsync
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system call first appeared in
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.Fx 7.0 .
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