table of contents
PHYSIO(9) | Kernel Developer's Manual | PHYSIO(9) |
NAME¶
physio — initiate I/O on raw devicesSYNOPSIS¶
#include <sys/param.h>#include <sys/systm.h>
#include <sys/bio.h>
#include <sys/buf.h> int
physio(dev_t 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 NetBSD with minor changes for applicability with FreeBSD. The physio call has been completely re-written for providing higher I/O and paging performance.July 8, 2004 | Debian |