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NAME    [Toc]    [Back]

     physio -- initiate I/O on raw devices

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     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

     Since uio normally describes user space addresses, physio() needs to lock
     the process into memory.  This is done by setting the P_PHYSIO flag on
     the process.  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.

RETURN VALUES    [Toc]    [Back]

     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    [Toc]    [Back]

     read(2), write(2)

HISTORY    [Toc]    [Back]

     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.

FreeBSD 5.2.1			 June 15, 1996			 FreeBSD 5.2.1
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