PHYSIO(9) BSD Kernel Developer's Manual PHYSIO(9)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);
DESCRIPTIONPhysread() 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 DFLTPHYS 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 struc‐
ture, 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.
SEE ALSOread(2), write(2), uio(9)BSD November 9, 2008 BSD
