1.\" $NetBSD: write.2,v 1.12 1998/08/29 08:32:43 lukem Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. 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.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)write.2 8.5 (Berkeley) 4/2/94 35.\" 36.Dd April 2, 1994 37.Dt WRITE 2 38.Os BSD 4 39.Sh NAME 40.Nm write , 41.Nm writev , 42.Nm pwrite , 43.Nm pwritev 44.Nd write output 45.Sh SYNOPSIS 46.Fd #include <sys/types.h> 47.Fd #include <sys/uio.h> 48.Fd #include <unistd.h> 49.Ft ssize_t 50.Fn write "int d" "const void *buf" "size_t nbytes" 51.Ft ssize_t 52.Fn writev "int d" "const struct iovec *iov" "int iovcnt" 53.Ft ssize_t 54.Fn pwrite "int d" "const void *buf" "size_t nbytes" "off_t offset" 55.Ft ssize_t 56.Fn pwritev "int d" "const struct iovec *iov" "int iovcnt" "off_t offset" 57.Sh DESCRIPTION 58.Fn write 59attempts to write 60.Fa nbytes 61of data to the object referenced by the descriptor 62.Fa d 63from the buffer pointed to by 64.Fa buf . 65.Fn writev 66performs the same action, but gathers the output data 67from the 68.Fa iovcnt 69buffers specified by the members of the 70.Fa iov 71array: iov[0], iov[1], ..., iov[iovcnt\|-\|1]. 72.Fn pwrite 73and 74.Fn pwritev 75perform the same functions, but write to the specified position in 76the file without modifying the file pointer. 77.Pp 78For 79.Fn writev 80and 81.Fn pwritev , 82the 83.Fa iovec 84structure is defined as: 85.Pp 86.Bd -literal -offset indent -compact 87struct iovec { 88 void *iov_base; 89 size_t iov_len; 90}; 91.Ed 92.Pp 93Each 94.Fa iovec 95entry specifies the base address and length of an area 96in memory from which data should be written. 97.Fn writev 98will always write a complete area before proceeding 99to the next. 100.Pp 101On objects capable of seeking, the 102.Fn write 103starts at a position 104given by the pointer associated with 105.Fa d 106(see 107.Xr lseek 2 ) . 108Upon return from 109.Fn write , 110the pointer is incremented by the number of bytes which were written. 111.Pp 112Objects that are not capable of seeking always write from the current 113position. The value of the pointer associated with such an object 114is undefined. 115.Pp 116If the real user is not the super-user, then 117.Fn write 118clears the set-user-id bit on a file. 119This prevents penetration of system security 120by a user who 121.Dq captures 122a writable set-user-id file 123owned by the super-user. 124.Pp 125When using non-blocking I/O on objects such as sockets that are subject 126to flow control, 127.Fn write 128and 129.Fn writev 130may write fewer bytes than requested; 131the return value must be noted, 132and the remainder of the operation should be retried when possible. 133.Sh RETURN VALUES 134Upon successful completion the number of bytes which were written 135is returned. Otherwise a -1 is returned and the global variable 136.Va errno 137is set to indicate the error. 138.Sh ERRORS 139.Fn write , 140.Fn writev , 141.Fn pwrite , 142and 143.Fn pwritev 144will fail and the file pointer will remain unchanged if: 145.Bl -tag -width Er 146.It Bq Er EBADF 147.Fa d 148is not a valid descriptor open for writing. 149.It Bq Er EPIPE 150An attempt is made to write to a pipe that is not open 151for reading by any process. 152.It Bq Er EPIPE 153An attempt is made to write to a socket of type 154.Dv SOCK_STREAM 155that is not connected to a peer socket. 156.It Bq Er EFBIG 157An attempt was made to write a file that exceeds the process's 158file size limit or the maximum file size. 159.It Bq Er EFAULT 160Part of 161.Fa iov 162or data to be written to the file 163points outside the process's allocated address space. 164.It Bq Er EINVAL 165The pointer associated with 166.Fa d 167was negative. 168.It Bq Er EINVAL 169The total length of the I/O is more than can be expressed by the ssize_t 170return value. 171.It Bq Er ENOSPC 172There is no free space remaining on the file system 173containing the file. 174.It Bq Er EDQUOT 175The user's quota of disk blocks on the file system 176containing the file has been exhausted. 177.It Bq Er EIO 178An I/O error occurred while reading from or writing to the file system. 179.It Bq Er EAGAIN 180The file was marked for non-blocking I/O, 181and no data could be written immediately. 182.El 183.Pp 184In addition, 185.Fn writev 186and 187.Fn pwritev 188may return one of the following errors: 189.Bl -tag -width Er 190.It Bq Er EINVAL 191.Fa iovcnt 192was less than or equal to 0, or greater than 193.Dv {IOV_MAX} . 194.It Bq Er EINVAL 195One of the 196.Fa iov_len 197values in the 198.Fa iov 199array was negative. 200.It Bq Er EINVAL 201The sum of the 202.Fa iov_len 203values in the 204.Fa iov 205array overflowed a 32-bit integer. 206.El 207.Pp 208.The 209.Fn pwrite 210and 211.Fn pwritev 212calls may also return the following errors: 213.Bl -tag -width Er 214.It Bq Er EINVAL 215The specified file offset is invalid. 216.It Bq Er ESPIPE 217The file descriptor is associated with a pipe, socket, or FIFO. 218.El 219.Sh SEE ALSO 220.Xr fcntl 2 , 221.Xr lseek 2 , 222.Xr open 2 , 223.Xr pipe 2 , 224.Xr poll 2 , 225.Xr select 2 226.Sh STANDARDS 227The 228.Fn write 229function is expected to conform to 230.St -p1003.1-88 . 231The 232.Fn writev 233and 234.Fn pwrite 235functions conform to 236.St -xpg4.2 . 237.Sh HISTORY 238the 239.Fn pwritev 240function call 241appeared in 242.Nx 1.4 . 243The 244.Fn pwrite 245function call 246appeared in 247.At V.4 . 248The 249.Fn writev 250function call 251appeared in 252.Bx 4.2 . 253The 254.Fn write 255function call appeared in 256.At v6 . 257