aio_fsync.3

xen 3.2.2 源码

.TH aio_fsync 3 2002-09-12 "Linux 2.4" Linux AIO"
.SH NAME
aio_fsync \- Synchronize a file's complete in-core state with that on disk
.SH SYNOPSYS
.nf
.B #include <errno.h>
.sp
.br 
.B #include <aio.h>
.sp
.br
.BI "int aio_fsync (int op, struct aiocb aiocbp)"
.fi
.SH DESCRIPTION
.PP
When dealing with asynchronous operations it is sometimes necessary to
get into a consistent state.  This would mean for AIO that one wants to
know whether a certain request or a group of request were processed.
This could be done by waiting for the notification sent by the system
after the operation terminated, but this sometimes would mean wasting
resources (mainly computation time).  Instead POSIX.1b defines two
functions which will help with most kinds of consistency.
.PP
The
.IR aio_fsync
and 
.IR "aio_fsync64"
functions are only available
if the symbol 
.IR "_POSIX_SYNCHRONIZED_IO"
is defined in 
.I unistd.h
.

Calling this function forces all I/O operations operating queued at the
time of the function call operating on the file descriptor
.IR "aiocbp->aio_fildes"
into the synchronized I/O completion state .  The 
.IR "aio_fsync"
function returns
immediately but the notification through the method described in
.IR "aiocbp->aio_sigevent"
will happen only after all requests for this
file descriptor have terminated and the file is synchronized.  This also
means that requests for this very same file descriptor which are queued
after the synchronization request are not affected.

If 
.IR "op"
is 
.IR "O_DSYNC"
the synchronization happens as with a call
to 
.IR "fdatasync"
.  Otherwise 
.IR "op"
should be 
.IR "O_SYNC"
and
the synchronization happens as with 
.IR "fsync"
.

As long as the synchronization has not happened, a call to
.IR "aio_error"
with the reference to the object pointed to by
.IR "aiocbp"
returns 
.IR "EINPROGRESS"
.  Once the synchronization is
done 
.IR "aio_error"
return 
.IR 0
if the synchronization was not
successful.  Otherwise the value returned is the value to which the
.IR "fsync"
or 
.IR "fdatasync"
function would have set the
.IR "errno"
variable.  In this case nothing can be assumed about the
consistency for the data written to this file descriptor.

.SH "RETURN VALUES"
The return value of this function is 
.IR 0
if the request was
successfully enqueued.  Otherwise the return value is 
.IR -1
and
.IR "errno".
.SH ERRORS
.TP
.B EAGAIN
The request could not be enqueued due to temporary lack of resources.
.TP
.B EBADF
The file descriptor 
.IR "aiocbp->aio_fildes"
is not valid or not open
for writing.
.TP
.B EINVAL
The implementation does not support I/O synchronization or the 
.IR "op"
parameter is other than 
.IR "O_DSYNC"
and 
.IR "O_SYNC"
.
.TP
.B ENOSYS
This function is not implemented.
.PP
When the sources are compiled with 
.IR "_FILE_OFFSET_BITS == 64"
 this
function is in fact 
.IR "aio_return64"
since the LFS interface
transparently replaces the normal implementation.
.SH "SEE ALSO"
.BR aio(3),
.BR aio_cancel(3),
.BR aio_cancel64(3),
.BR aio_error(3),
.BR aio_error64(3),
.BR aio_fsync64(3),
.BR aio_init(3),
.BR aio_read(3),
.BR aio_read64(3),
.BR aio_return(3),
.BR aio_return64(3),
.BR aio_suspend(3),
.BR aio_suspend64(3),
.BR aio_write(3),
.BR aio_write64(3),
.BR errno(3),