aio_read.3

xen 3.2.2 源码

.TH aio_read 3 2002-09-12 "Linux 2.4" Linux AIO"
.SH NAME
aio_read \- Initiate an asynchronous read operation
.SH SYNOPSYS
.nf
.B #include <errno.h>
.sp
.br 
.B #include <aio.h>
.sp
.br
.BI "int aio_read (struct aiocb *aiocbp)"
.fi
.SH DESCRIPTION
This function initiates an asynchronous read operation.  It
immediately returns after the operation was enqueued or when an
error was encountered.

The first 
.IR "aiocbp->aio_nbytes"
bytes of the file for which
.IR "aiocbp->aio_fildes"
is a descriptor are written to the buffer
starting at 
.IR "aiocbp->aio_buf"
.  Reading starts at the absolute
position 
.IR "aiocbp->aio_offset"
in the file.

If prioritized I/O is supported by the platform the
.IR "aiocbp->aio_reqprio"
value is used to adjust the priority before
the request is actually enqueued.

The calling process is notified about the termination of the read
request according to the 
.IR "aiocbp->aio_sigevent"
value.

.SH "RETURN VALUES"
When 
.IR "aio_read"
returns, the return value is zero if no error
occurred that can be found before the process is enqueued.  If such an
early error is found, the function returns 
.IR -1
and sets
.IR "errno".

.PP
If 
.IR "aio_read"
returns zero, the current status of the request
can be queried using 
.IR "aio_error"
and 
.IR "aio_return"
functions.
As long as the value returned by 
.IR "aio_error"
is 
.IR "EINPROGRESS"
the operation has not yet completed.  If 
.IR "aio_error"
returns zero,
the operation successfully terminated, otherwise the value is to be
interpreted as an error code.  If the function terminated, the result of
the operation can be obtained using a call to 
.IR "aio_return"
.  The
returned value is the same as an equivalent call to 
.IR "read"
would
have returned.  
When the sources are compiled with 
.IR "_FILE_OFFSET_BITS == 64"
this
function is in fact 
.IR "aio_read64"
since the LFS interface transparently
replaces the normal implementation.

.SH ERRORS
In the case of an early error:
.TP
.B  EAGAIN
The request was not enqueued due to (temporarily) exceeded resource
limitations.
.TP
.B  ENOSYS
The 
.IR "aio_read"
function is not implemented.
.TP
.B  EBADF
The 
.IR "aiocbp->aio_fildes"
descriptor is not valid.  This condition
need not be recognized before enqueueing the request and so this error
might also be signaled asynchronously.
.TP
.B  EINVAL
The 
.IR "aiocbp->aio_offset"
or 
.IR "aiocbp->aio_reqpiro"
value is
invalid.  This condition need not be recognized before enqueueing the
request and so this error might also be signaled asynchronously.

.PP
In the case of a normal return, possible error codes returned by 
.IR "aio_error"
are:
.TP
.B  EBADF
The 
.IR "aiocbp->aio_fildes"
descriptor is not valid.
.TP
.B  ECANCELED
The operation was canceled before the operation was finished
.TP
.B  EINVAL
The 
.IR "aiocbp->aio_offset"
value is invalid.
.PP
.SH "SEE ALSO"
.BR aio(3),
.BR aio_cancel(3),
.BR aio_cancel64(3),
.BR aio_error(3),
.BR aio_error64(3),
.BR aio_fsync(3),
.BR aio_fsync64(3),
.BR aio_init(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),