Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
PHYSIO(9)		    Kernel Developer's Manual		       PHYSIO(9)

NAME
     physio -- initiate I/O on raw devices

SYNOPSIS
     #include <sys/param.h>
     #include <sys/systm.h>
     #include <sys/bio.h>
     #include <sys/buf.h>

     int
     physio(struct cdev *dev, struct uio *uio, int ioflag);

DESCRIPTION
     The  physio()  is	a helper function typically called from character device
     read() and write() routines to start I/O on a  user  process  buffer.   The
     maximum  amount  of  data	to  transfer  with  each  call	is determined by
     dev->si_iosize_max.  The physio() call converts  the  I/O	request  into  a
     strategy()  request  and  passes the new request to the driver's strategy()
     routine for processing.

     Since uio normally describes user space addresses, physio() needs	to  lock
     those  pages into memory.	This is done by calling vmapbuf() for the appro-
     priate pages.  physio() always awaits the	completion  of	the  entire  re-
     quested  transfer	before	returning, unless an error condition is detected
     earlier.

     A break-down of the arguments follows:

     dev     The device number identifying the device to interact with.

     uio     The description of the entire transfer as	requested  by  the  user
	     process.	Currently,  the  results of passing a uio structure with
	     the uio_segflg set to anything other than UIO_USERSPACE  are  unde-
	     fined.

     ioflag  The  ioflag  argument  from  the read() or write() function calling
	     physio().

RETURN VALUES
     If successful physio() returns 0.	EFAULT is returned if the address  range
     described	by  uio  is  not accessible by the requesting process.	physio()
     will return any error resulting from calls to the device strategy	routine,
     by  examining the B_ERROR buffer flag and the b_error field.  Note that the
     actual transfer size may be less than requested by uio if the  device  sig-
     nals an "end of file" condition.

SEE ALSO
     read(2), write(2)

HISTORY
     The physio manual page is originally from NetBSD with minor changes for ap-
     plicability with FreeBSD.

     The physio call has been completely re-written for providing higher I/O and
     paging performance.

FreeBSD ports 15.quarterly	January 19, 2012		       PHYSIO(9)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=physio&sektion=9&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

home | help