NAME
physread,
physwrite —
initiate I/O on raw devices
SYNOPSIS
#include
<sys/buf.h>
#include <sys/device.h>
int
physread(struct
dev_read_args *ap);
int
physwrite(struct
dev_write_args *ap);
DESCRIPTION
Physread()
and
physwrite()
are helper functions typically called from character device read and write
routines to start I/O on a user process buffer. They will call the
dev_dstrategy()
routine one or more times depending on the size of transfer which is described
by the ap argument.
The maximum amount of data transferable in one
iteration of the
physread()
and
physwrite()
functions is determined by the maximum I/O size supported by the device
dev, otherwise the value of
MAXPHYS is used. Until the I/O operation is
complete, the calling process or thread is put to sleep with the wait
message set to ‘physstr’.
The
physread()
and
physwrite()
functions always await the completion of the entire requested transfer
before returning, unless an error condition is detected earlier.
The ap argument is a pointer to a
dev_read_args or dev_write_args
structure, as passed to d_read or
d_write.
RETURN VALUES
If successful physread() and
physwrite() will return 0.
The errno value
EFAULT will be returned if the address range
described by uio is not accessible by the calling
process or thread.
Note that the actual transfer size may be less than requested by ap if the device signals an “end of file” condition.