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

       Solaris DDI specific (Solaris 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 automati-
		       cally 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 spec-
       ified 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 com-
       pleted 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  min-
       phys().

       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.

SunOS 5.10							    2 Apr 1993								physio(9F)