$NetBSD: physio.9,v 1.2 1996/11/11 00:05:12 lukem Exp $ Copyright (c) 1996 The NetBSD Foundation, Inc. All rights reserved. This code is derived from software contributed to The NetBSD Foundation by Paul Kranenburg. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following discla...
NAMEphysio - initiate I/O on raw devices
SYNOPSISIn sys/param.h In sys/systm.h In sys/bio.h In sys/buf.h Ft int Fn physio struct cdev *dev struct uio *uio int ioflag
DESCRIPTIONThe Fn physio is a helper function typically called from character device Fn read and Fn write routines to start I/O on a user process buffer. The maximum amount of data to transfer with each call is determined by Fa dev->si_iosize_max . The Fn physio call converts the I/O request into a Fn strategy request and passes the new request to the driver's Fn strategy routine for processing.
Since Fa uio normally describes user space addresses, Fn physio needs to lock those pages into memory. This is done by calling Fn vmapbuf for the appropriate pages. Fn physio always awaits the completion of the entire requested transfer before returning, unless an error condition is detected earlier.
A break-down of the arguments follows:
- Fa dev
- The device number identifying the device to interact with.
- Fa uio
- The description of the entire transfer as requested by the user process. Currently, the results of passing a Fa uio structure with the uio_segflg set to anything other than UIO_USERSPACE are undefined.
- Fa ioflag
- The ioflag argument from the Fn read or Fn write function calling Fn physio .
RETURN VALUESIf successful Fn physio returns 0. Er EFAULT is returned if the address range described by Fa uio is not accessible by the requesting process. Fn 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 Fa uio if the device signals an ``end of file'' condition.
SEE ALSOread(2), write(2)
HISTORYThe sysctl Cm net.inet.tcp.syncookies manual page is originally from Nx with minor changes for applicability with Fx .
The sysctl Cm net.inet.tcp.syncookies call has been completely re-written for providing higher I/O and paging performance.