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Man Pages


Manual Reference Pages  -  PHYSIO (9)

NAME

physio - initiate I/O on raw devices

CONTENTS

Synopsis
Description
Return Values
See Also
History

SYNOPSIS


.In sys/param.h
.In sys/systm.h
.In sys/bio.h
.In 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 appropriate pages. 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:
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 undefined.
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 signals an "end of file" condition.

SEE ALSO

read(2), write(2)

HISTORY

The physio manual page is originally from
.Nx with minor changes for applicability with
.Fx .

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

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