PHYSIO(9) OpenBSD Kernel Manual PHYSIO(9)NAMEphysio - initiate I/O on raw devices
SYNOPSIS
int
physio(void (*strategy)(struct buf *), dev_t dev, int flags, void
(*minphys)(struct buf *), struct uio *uio);
DESCRIPTIONphysio() is a helper function typically called from character device read
and write routines to start I/O on a user process buffer. It calls back
on the provided strategy routine one or more times to complete the
transfer described by uio. The maximum amount of data to transfer with
each call to strategy is determined by the minphys routine. Since uio
normally describes user space addresses, physio() needs to lock the
appropriate data area into memory before each transaction with strategy
(see the uvm_vslock() and uvm_vsunlock() functions in uvm(9)). physio()
always awaits the completion of the entire requested transfer before
returning, unless an error condition is detected earlier.
In all cases, a temporary buffer is allocated from a system pool. This
buffer will have the B_BUSY, B_PHYS, and B_RAW flags set when passed to
the strategy routine.
A break-down of the arguments follows:
strategy
The device strategy routine to call for each chunk of data to
initiate device I/O.
dev The device number identifying the device to interact with.
flags Direction of transfer; the only valid settings are B_READ or
B_WRITE.
minphys
A device specific routine called to determine the maximum
transfer size that the device's strategy routine can handle.
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
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 ALSOread(2), write(2)OpenBSD 4.9 September 22, 2010 OpenBSD 4.9
