'\" te
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.\" Copyright 1989 AT&T
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.TH UIO 9S "Mar 26, 2009"
.SH NAME
uio \- scatter/gather I/O request structure
.SH SYNOPSIS
.LP
.nf
#include <sys/uio.h>
.fi

.SH INTERFACE LEVEL
.sp
.LP
Architecture independent level 1 (DDI/DKI)
.SH DESCRIPTION
.sp
.LP
A  \fBuio\fR structure describes an \fBI/O \fRrequest that can be broken up
into different data storage areas (scatter/gather I/O). A request is a list of
\fBiovec\fR structures (base-length pairs) indicating where in user space or
kernel space the \fBI/O \fRdata is to be read or written.
.sp
.LP
The contents of  \fBuio\fR structures passed to the driver through the entry
points should not be written by the driver. The  \fBuiomove\fR(9F) function
takes care of all overhead related to maintaining the state of the \fBuio\fR
structure.
.sp
.LP
\fBuio\fR structures allocated by the driver should be initialized to zero
before use, by \fBbzero\fR(9F), \fBkmem_zalloc\fR(9F), or an equivalent.
.SH STRUCTURE MEMBERS
.sp
.in +2
.nf
iovec_t      *uio_iov;      /* pointer to start of iovec */
                            /* list for uio struc. */
int          uio_iovcnt;    /* number of iovecs in list */
off_t        uio_offset;    /* 32-bit offset into file where
                            /* data is xferred. See NOTES. */
offset_t     uio_loffset;   /* 64-bit offset into file where */
                            /* data is xferred. See NOTES. */
uio_seg_t    uio_segflg;    /* ID's type of I/O transfer: */
                            /* UIO_SYSSPACE:  kernel <-> kernel */
                            /* UIO_USERSPACE: kernel <-> user */
uint16_t     uio_fmode;     /* file mode flags (not driver setable) */
daddr_t      uio_limit;     /* 32-bit ulimit for file (max. block */
                            /* offset). not driver setable. */
                            /* See NOTES. */
diskaddr_t   uio_llimit;    /* 64-bit ulimit for file (max. block */
                            /* offset). not driver setable. */
                            /* See NOTES */
ssize_t      uio_resid;     /* residual count */
.fi
.in -2

.sp
.LP
The  \fBuio_iov\fR member is a pointer to the beginning of the \fBiovec\fR(9S)
list for the  \fBuio\fR. When the \fBuio\fR structure is passed to the driver
through an entry point, the driver should not set  \fBuio_iov\fR. When the
\fBuio\fR structure is created by the driver,  \fBuio_iov\fR should be
initialized by the driver and not written to afterward.
.SH SEE ALSO
.sp
.LP
.BR aread (9E),
.BR awrite (9E),
.BR read (9E),
.BR write (9E),
.BR bzero (9F),
.BR kmem_zalloc (9F),
.BR uiomove (9F),
.BR cb_ops (9S),
.BR iovec (9S)
.sp
.LP
\fIWriting Device Drivers\fR
.SH NOTES
.sp
.LP
Only one structure, \fBuio_offset\fR or \fBuio_loffset\fR, should be
interpreted by the driver. Which field the driver interprets is dependent upon
the settings in the \fBcb_ops\fR(9S) structure.
.sp
.LP
Only one structure, \fBuio_limit\fR or \fBuio_llimit\fR, should be interpreted
by the driver. Which field the driver interprets is dependent upon the settings
in the \fBcb_ops\fR(9S) structure.
.sp
.LP
When performing \fBI/O \fRon a seekable device, the driver should not modify
either the \fBuio_offset\fR or the \fBuio_loffset\fR field of the \fBuio\fR
structure. \fBI/O \fRto such a device is constrained by the maximum offset
value. When performing \fBI/O \fRon a device on which the concept of position
has no relevance, the driver may preserve the \fBuio_offset\fR or
\fBuio_loffset\fR, perform the \fBI/O \fRoperation, then restore the
\fBuio_offset\fR or \fBuio_loffset\fR to the field's initial value. \fBI/O
\fRperformed to a device in this manner is not constrained.