.if n .pH ddi.rm/d2/gen/write @(#)write	43.9 of 11/25/92
.\" Copyright 1992, 1991 UNIX System Laboratories, Inc.
.TH write D2
.IX "\f4write\fP(D2)"
.SH NAME
\f4write\fP \- write data to a device
.SH SYNOPSIS
.nf
.na
.ft 4
#include <sys/types.h>
#include <sys/errno.h>
#include <sys/uio.h>
#include <sys/cred.h>
#include <sys/ddi.h>
.sp 0.4
int \f2prefix\fPwrite(dev_t \f2dev\fP, uio_t *\f2uiop\fP, cred_t *\f2crp\fP);
.ft 1
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.SS Arguments
.RS 0
.TP 10
\f2dev\fP
Device number.
.TP
\f2uiop\fP
Pointer to the \f4uio\fP(D4) structure that describes where the data
is to be fetched from user space.
.TP
\f2crp\fP
Pointer to the user credential structure for the I/O
transaction.
.RE
.SH DESCRIPTION
The driver \f4write\fP routine is called
during the \f4write\fP(2) system call.
The \f4write\fP routine is responsible for transferring data from
the user data area to the device.
.SS "Return Values"
The \f4write\fP routine should return 0 for success,
or the appropriate error number.
.SH USAGE
This entry point is optional,
and is valid for character device drivers only.
.P
The pointer to the user credentials, \f2crp\fP, is available
so the driver can check to see if the user can write privileged
information, if the driver provides access to any.
The \f4uio\fP structure provides the information necessary to determine
how much data should be transferred.
The \f4uiomove\fP(D3) function provides
a convenient way to copy data using the \f4uio\fP structure.
.P
Block drivers that provide a character interface can use \f4physiock\fP(D3) to
perform the data transfer with the driver's \f4strategy\fP(D2) routine.
.SS "Synchronization Constraints"
The \f4write\fP routine has user context and can sleep.
.P
The write operation is intended to be synchronous from the caller's perspective.
Minimally, the driver \f4write\fP routine should not return until the caller's
buffer is no longer needed.
For drivers that care about returning errors, the data should be committed
to the device.
For others, the data might only be copied to local staging buffers.
Then the data will be committed to the device asynchronously
to the user's request,
losing the ability to return an error with the associated request.
.SH REFERENCES
.na
\f4drv_priv\fP(D3),
\f4errnos\fP(D5),
\f4physiock\fP(D3),
\f4read\fP(D2),
\f4strategy\fP(D2),
\f4uio\fP(D4),
\f4uiomove\fP(D3),
\f4uwritec\fP(D3)
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