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$FreeBSD: head/share/man/man9/physio.9 58901 2000-04-01 20:31:07Z asmodai $
.Dd June 15, 1996 .Dt PHYSIO 9 .Os FreeBSD .Sh NAME .Nm physio .Nd initiate I/O on raw devices .Sh SYNOPSIS .Fd #include <sys/param.h> .Fd #include <sys/systm.h> .Fd #include <sys/buf.h> .Ft int .Fn physio "dev_t dev" "struct uio *uio" "int ioflag" .Sh DESCRIPTION The .Fn 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 .Fa strategy routine one or more times to complete the transfer described by .Fa uio . The maximum amount of data to transfer with each call to .Fa strategy is determined by the .Fa minphys routine. Since .Fa uio normally describes user space addresses, .Fn physio needs to lock the process into memory. This is done by setting the .Dv P_PHYSIO flag on the process. .Fn physio always awaits the completion of the entire requested transfer before returning, unless an error condition is detected earlier. In all cases, the buffer passed in .Fa bp is locked (marked as .Dq busy ) for the duration of the entire transfer.
p A break-down of the arguments follows: l -tag -width indent t Fa strategy The device strategy routine to call for each chunk of data to initiate device I/O. t Fa bp The buffer to use with the strategy routine. The buffer flags will have .Dv B_BUSY , and .Dv B_PHYS set when passed to the strategy routine. If .Dv NULL , a buffer is allocated from a system pool. t Fa dev The device number identifying the device to interact with. t Fa flags Direction of transfer; the only valid settings are .Dv B_READ or .Dv B_WRITE . t Fa minphys A device specific routine called to determine the maximum transfer size that the device's strategy routine can handle. t Fa uio The description of the entire transfer as requested by the user process. Currently, the results of passing a .Fa uio structure with the .Sq uio_segflg set to anything other than .Dv UIO_USERSPACE , are undefined. .El
p .Sh RETURN VALUES If successful .Fn physio returns 0. .Er EFAULT is returned if the address range described by .Fa uio is not accessible by the requesting process. .Fn physio will return any error resulting from calls to the device strategy routine, by examining the .Dv B_ERROR buffer flag and the .Va b_error field. Note that the actual transfer size may be less than requested by .Fa uio if the device signals an .Dq end of file condition. .Sh SEE ALSO .Xr read 2 , .Xr write 2