xref: /illumos-gate/usr/src/man/man9e/read.9e (revision bbf21555)
Copyright 1989 AT&T
Copyright (c) 1997, Sun Microsystems, Inc. All Rights Reserved
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READ 9E "Nov 19, 1997"
read - read data from a device

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/open.h>
#include <sys/uio.h>
#include <sys/cred.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>

int prefixread(dev_t dev, struct uio *uio_p, cred_t *cred_p);

Architecture independent level 1 (DDI/DKI). This entry point is optional.


Device number.


Pointer to the uio(9S) structure that describes where the data is to be stored in user space.


Pointer to the user credential structure for the I/O transaction.


The driver read() routine is called indirectly through cb_ops(9S) by the read(2) system call. The read() routine should check the validity of the minor number component of dev and the user credential structure pointed to by cred_p (if pertinent). The read() routine should supervise the data transfer into the user space described by the uio(9S) structure.


The read() routine should return 0 for success, or the appropriate error number.


Example 1 read() routine using physio()

The following is an example of a read() routine using physio(9F) to perform reads from a non-seekable device:

 static int
 xxread(dev_t dev, struct uio *uiop, cred_t *credp)
 int rval;
 offset_t off;
 int instance;
 xx_t xx;

 instance = getminor(dev);
 xx = ddi_get_soft_state(xxstate, instance);
 if (xx == NULL)
 return (ENXIO);
 off = uiop->uio_loffset;
 rval = physio(xxstrategy, NULL, dev, B_READ,
 xxmin, uiop);
 uiop->uio_loffset = off;
 return (rval);

read (2), write (9E), physio (9F), cb_ops (9S), uio (9S)

Writing Device Drivers