'\" te
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.TH AREAD 9E "Mar 28, 1997"
.SH NAME
aread \- asynchronous read from a device
.SH SYNOPSIS
.nf
#include <sys/uio.h>
#include <sys/aio_req.h>
#include <sys/cred.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
int\fIprefix\fR

\fB\fR\fBaread\fR(\fBdev_t\fR \fIdev\fR, \fBstruct aio_req *\fR\fIaio_reqp\fR, \fBcred_t *\fR\fIcred_p\fR);
.fi

.SH INTERFACE LEVEL
illumos \fBDDI \fRspecific (illumos DDI). This entry point is \fIoptional\fR.
Drivers that do not support an \fBaread()\fR entry point should use
.BR nodev (9F)
.SH PARAMETERS
.ne 2
.na
\fB\fIdev\fR \fR
.ad
.RS 13n
Device number.
.RE

.sp
.ne 2
.na
\fB\fIaio_reqp\fR \fR
.ad
.RS 13n
Pointer to the \fBaio_req\fR(9S) structure that describes where the data is to
be stored.
.RE

.sp
.ne 2
.na
\fB\fIcred_p\fR \fR
.ad
.RS 13n
Pointer to the credential structure.
.RE

.SH DESCRIPTION
The driver's \fBaread()\fR routine is called to perform an asynchronous read.
\fBgetminor\fR(9F) can be used to access the minor number component of the
\fIdev\fR argument. \fBaread()\fR may use the credential structure pointed to
by \fIcred_p\fR to check for superuser access by calling \fBdrv_priv\fR(9F).
The \fBaread()\fR routine may also examine the \fBuio\fR(9S) structure through
the \fBaio_req\fR structure pointer, \fIaio_reqp\fR. \fBaread()\fR must call
\fBaphysio\fR(9F) with the \fBaio_req\fR pointer and a pointer to the driver's
\fBstrategy\fR(9E) routine.
.sp
.LP
No fields of the \fBuio\fR(9S) structure pointed to by \fBaio_req\fR, other
than \fBuio_offset\fR or \fBuio_loffset\fR, may be modified for non-seekable
devices.
.SH RETURN VALUES
The \fBaread()\fR routine should return \fB0\fR for success, or the appropriate
error number.
.SH CONTEXT
This function is called from user context only.
.SH EXAMPLES
\fBExample 1 \fRThe following is an example of an \fBaread()\fR routine:
.sp
.in +2
.nf
static int
xxaread(dev_t dev, struct aio_req *aio, cred_t *cred_p)
{
	int instance;
	struct xxstate *xsp;
	instance = getminor(dev);
	xsp = ddi_get_soft_state(statep, instance);
	/*Verify soft state structure has been allocated */
	if (xsp == NULL)
		return (ENXIO);
	return (aphysio(xxstrategy, anocancel,
					dev, B_READ, xxminphys, aio));
}
.fi
.in -2

.SH SEE ALSO
.BR read (2),
.BR aioread (3C),
.BR awrite (9E),
.BR read (9E),
.BR strategy (9E),
.BR write (9E),
.BR anocancel (9F),
.BR aphysio (9F),
.BR ddi_get_soft_state (9F),
.BR drv_priv (9F),
.BR getminor (9F),
.BR minphys (9F),
.BR nodev (9F),
.BR aio_req (9S),
.BR cb_ops (9S),
.BR uio (9S)
.sp
.LP
\fIWriting Device Drivers\fR
.SH BUGS
There is no way other than calling \fBaphysio\fR(9F) to accomplish an
asynchronous read.