man/man9f/physio.9f

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 PHYSIO 9F "Apr 2, 1993"
 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.