#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
Fa 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
Fa 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:
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
read ();
or
write ();
function calling
physio (.);
RETURN VALUES
If successful
physio ();
returns 0.
Er EFAULT
is returned if the address range described by
Fa 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
Fa uio
if the device signals an
``end of file''
condition.
