|PHYSIO(9)||Kernel Developer's Manual||PHYSIO(9)|
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_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_RAW flags set
when passed to the strategy routine.
A break-down of the arguments follows:
UIO_USERSPACE, are undefined.
physio() returns 0.
EFAULTis 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_ERRORbuffer 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|