uio(9S) 						    Data Structures for Drivers 						   uio(9S)

NAME

       uio - scatter/gather I/O request structure

SYNOPSIS

       #include <sys/uio.h>

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI)

DESCRIPTION

       A  uio structure describes an I/O request that can be broken up into different data storage areas (scatter/gather I/O). A request is a list
       of  iovec structures (base-length pairs) indicating where in user space or kernel space the I/O data is to be read or written.

       The contents of	uio structures passed to the driver through the entry points should not be written by the driver.  The	uiomove(9F)  func-
       tion takes care of all overhead related to maintaining the state of the uio structure.

       uio structures allocated by the driver should be initialized to zero before use, by bzero(9F), kmem_zalloc(9F), or an equivalent.

STRUCTURE MEMBERS

       iovec_t	    *uio_iov;	   /* pointer to the start of the iovec */
				   /* list for the uio structure */
       int	    uio_iovcnt;    /* the number of iovecs in the list */
       off_t	    uio_offset;    /* 32-bit offset into file where data is */
				   /* transferred from or to. See NOTES. */
       offset_t     uio_loffset;   /* 64-bit offset into file where data is */
				   /* transferred from or to. See NOTES. */
       uio_seg_t    uio_segflg;    /* identifies the type of I/O transfer: */
				   /*	 UIO_SYSSPACE:	kernel <-> kernel */
				   /*	 UIO_USERSPACE: kernel <-> user */
       short	    uio_fmode;	   /* file mode flags (not driver setable) */
       daddr_t	    uio_limit;	   /* 32-bit ulimit for file (maximum block */
				   /* offset). not driver setable. See NOTES. */
       diskaddr_t   uio_llimit;    /* 64-bit ulimit for file (maximum block */
				   /* offset). not driver setable. See NOTES. */
       int	    uio_resid;	   /* residual count */

       The   uio_iov  member  is  a  pointer  to  the beginning of the iovec(9S) list for the  uio. When the uio structure is passed to the driver
       through an entry point, the driver should not set  uio_iov. When the  uio structure is created by the driver,  uio_iov should  be  initial-
       ized by the driver and not written to afterward.

SEE ALSO

       aread(9E), awrite(9E), read(9E), write(9E), bzero(9F), kmem_zalloc(9F), uiomove(9F), cb_ops(9S), iovec(9S)

       Writing Device Drivers

NOTES

       Only one structure, uio_offset or uio_loffset, should be interpreted by the driver. Which field the driver interprets is dependent upon the
       settings in the cb_ops(9S) structure.

       Only one structure, uio_limit or uio_llimit, should be interpreted by the driver. Which field the driver interprets is dependent  upon  the
       settings in the cb_ops(9S) structure.

       When performing I/O on a seekable device, the driver should not modify either the uio_offset or the uio_loffset field of the uio structure.
       I/O to such a device is constrained by the maximum offset value. When performing I/O on a device on which the concept of  position  has	no
       relevance,  the driver may preserve the uio_offset or uio_loffset, perform the I/O operation, then restore the uio_offset or uio_loffset to
       the field's initial value. I/O performed to a device in this manner is not constrained.

SunOS 5.10							    28 Mar 1997 							   uio(9S)