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physio.9freebsd

BSD mandoc

NAME

physio - initiate I/O on raw devices

SYNOPSIS

In sys/param.h In sys/systm.h In sys/bio.h In sys/buf.h Ft int Fn physio dev_t dev struct uio *uio int ioflag

DESCRIPTION

The 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 VALUES

If 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 ALSO

read(2), write(2)

HISTORY

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

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