PHYSIO(9) | Kernel Developer's Manual | PHYSIO(9) |
physio
—
physio
(void (*strategy)(struct buf
*), dev_t dev, int flags,
void (*minphys)(struct buf *), struct
uio *uio);
physio
() 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:
B_READ
or B_WRITE
.UIO_USERSPACE
, are undefined.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.
September 14, 2015 | OpenBSD-current |