1.\" $NetBSD: uiomove.9,v 1.21 2023/05/22 14:07:24 riastradh Exp $ 2.\" 3.\" Copyright (c) 1996 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 16.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 17.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 18.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 19.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25.\" POSSIBILITY OF SUCH DAMAGE. 26.\" 27.Dd May 9, 2023 28.Dt UIOMOVE 9 29.Os 30.Sh NAME 31.Nm uiomove 32.Nd move data described by a struct uio 33.Sh SYNOPSIS 34.In sys/systm.h 35.Ft int 36.Fn uiomove "void *buf" "size_t n" "struct uio *uio" 37.Ft int 38.Fn uiopeek "void *buf" "size_t n" "struct uio *uio" 39.Ft void 40.Fn uioskip "void *buf" "size_t n" "struct uio *uio" 41.Sh DESCRIPTION 42The 43.Fn uiomove 44function copies up to 45.Fa n 46bytes between the kernel-space address pointed 47to by 48.Fa buf 49and the addresses described by 50.Fa uio , 51which may be in user-space or kernel-space. 52.Pp 53The 54.Fa uio 55argument is a pointer to a 56.Va struct uio 57as defined by 58.In sys/uio.h : 59.Bd -literal -offset indent 60struct uio { 61 struct iovec *uio_iov; 62 int uio_iovcnt; 63 off_t uio_offset; 64 size_t uio_resid; 65 enum uio_rw uio_rw; 66 struct vmspace *uio_vmspace; 67}; 68.Ed 69.Pp 70A 71.Va struct uio 72typically describes data in motion. 73Several of the fields described below reflect that expectation. 74.Bl -tag -width "uio_vmspace " 75.It Va uio_iov 76Pointer to array of 77.Tn I/O 78vectors to be processed. 79The 80.Va struct iovec 81is defined to be: 82.Bd -literal -offset indent 83struct iovec { 84 void *iov_base; 85 size_t iov_len; 86}; 87.Ed 88.Pp 89The members in the 90.Va struct iovec 91should only be initialized. 92These are: 93.Bl -tag -width "*iov_base " -offset indent 94.It Va iov_base 95The address for a range of memory to or from which data is transferred. 96.It Va iov_len 97The number of bytes of data to be transferred to 98or from the range of memory starting at 99.Va iov_base . 100.El 101.It Va uio_iovcnt 102The number of 103.Tn I/O 104vectors in the 105.Va uio_iov 106array. 107.It Va uio_offset 108An offset into the corresponding object. 109.It Va uio_resid 110The amount of space described by the structure; notionally, the amount 111of data remaining to be transferred. 112.It Va uio_rw 113A flag indicating whether data should be read into the space 114(UIO_READ) or written from the space (UIO_WRITE). 115.It Va uio_vmspace 116A pointer to the address space which is being transferred to or from. 117.El 118.Pp 119The value of 120.Va uio->uio_rw 121controls whether 122.Fn uiomove 123copies data from 124.Fa buf 125to 126.Fa uio 127or vice versa. 128.Pp 129The lesser of 130.Fa n 131or 132.Va uio->uio_resid 133bytes are copied. 134.Pp 135.Fn uiomove 136changes fields of the structure pointed to by 137.Fa uio , 138such that 139.Va uio->uio_resid 140is decremented by the amount of data moved, 141.Va uio->uio_offset 142is incremented by the same amount, and the array of iovecs is adjusted 143to point that much farther into the region described. 144This allows multiple calls to 145.Fn uiomove 146to easily be used to fill or drain the region of data. 147.Pp 148The 149.Fn uiopeek 150function copies up to 151.Fa n 152bytes of data without updating 153.Fa uio ; 154the 155.Fn uioskip 156function updates 157.Fa uio 158without copying any data, and is guaranteed never to sleep or fault 159even if the buffers are in userspace and memory access via 160.Fn uiomove 161or 162.Fn uiopeek 163would trigger paging. 164A successful 165.Fn uiomove buf n uio 166call is equivalent to a successful 167.Fn uiopeek buf n uio 168followed by 169.Fn uioskip n uio . 170.Sh RETURN VALUES 171Upon successful completion, 172.Fn uiomove 173and 174.Fn uiopeek 175return 0. 176If a bad address is encountered, 177.Er EFAULT 178is returned. 179.Sh SEE ALSO 180.Xr copy 9 , 181.Xr ufetch 9 , 182.Xr ustore 9 183