PHYSIO(9F) Kernel Functions for Drivers PHYSIO(9F)

NAME

physio, minphys - perform physical I/O

SYNOPSIS

#include <sys/types.h>
#include <sys/buf.h>
#include <sys/uio.h>


int physio(int(*strat)(struct buf *), struct buf *bp, dev_t dev,
int rw, void (*mincnt)(struct buf *), struct uio *uio);


void minphys(struct buf *bp);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

physio()
strat
Pointer to device strategy routine.


bp
Pointer to a buf(9S) structure describing the transfer. If bp
is set to NULL then physio() allocates one which is
automatically released upon completion.


dev
The device number.


rw
Read/write flag. This is either B_READ when reading from the
device, or B_WRITE when writing to the device.


mincnt
Routine which bounds the maximum transfer unit size.


uio
Pointer to the uio structure which describes the user I/O
request.


minphys()
bp
Pointer to a buf structure.

DESCRIPTION

physio() performs unbuffered I/O operations between the device dev and
the address space described in the uio structure.


Prior to the start of the transfer physio() verifies the requested
operation is valid by checking the protection of the address space
specified in the uio structure. It then locks the pages involved in the
I/O transfer so they can not be paged out. The device strategy routine,
strat(), is then called one or more times to perform the physical I/O
operations. physio() uses biowait(9F) to block until strat() has
completed each transfer. Upon completion, or detection of an error,
physio() unlocks the pages and returns the error status.


physio() uses mincnt() to bound the maximum transfer unit size to the
system, or device, maximum length. minphys() is the system mincnt()
routine for use with physio() operations. Drivers which do not provide
their own local mincnt() routines should call physio() with minphys().


minphys() limits the value of bp->b_bcount to a sensible default for the
capabilities of the system. Drivers that provide their own mincnt()
routine should also call minphys() to make sure they do not exceed the
system limit.

RETURN VALUES

physio() returns:

0
Upon success.


non-zero
Upon failure.

CONTEXT

physio() can be called from user context only.

SEE ALSO

strategy(9E), biodone(9F), biowait(9F), buf(9S), uio(9S)


Writing Device Drivers

WARNINGS

Since physio() calls biowait() to block until each buf transfer is
complete, it is the drivers responsibility to call biodone(9F) when the
transfer is complete, or physio() will block forever.

April 2, 1993 PHYSIO(9F)