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Diffstat (limited to 'lib/libc/sys/write.2')
| -rw-r--r-- | lib/libc/sys/write.2 | 286 |
1 files changed, 286 insertions, 0 deletions
diff --git a/lib/libc/sys/write.2 b/lib/libc/sys/write.2 new file mode 100644 index 0000000..6d60835 --- /dev/null +++ b/lib/libc/sys/write.2 @@ -0,0 +1,286 @@ +.\" Copyright (c) 1980, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)write.2 8.5 (Berkeley) 4/2/94 +.\" $FreeBSD$ +.\" +.Dd July 7, 2005 +.Dt WRITE 2 +.Os +.Sh NAME +.Nm write , +.Nm writev , +.Nm pwrite , +.Nm pwritev +.Nd write output +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In sys/types.h +.In sys/uio.h +.In unistd.h +.Ft ssize_t +.Fn write "int d" "const void *buf" "size_t nbytes" +.Ft ssize_t +.Fn pwrite "int d" "const void *buf" "size_t nbytes" "off_t offset" +.Ft ssize_t +.Fn writev "int d" "const struct iovec *iov" "int iovcnt" +.Ft ssize_t +.Fn pwritev "int d" "const struct iovec *iov" "int iovcnt" "off_t offset" +.Sh DESCRIPTION +The +.Fn write +system call +attempts to write +.Fa nbytes +of data to the object referenced by the descriptor +.Fa d +from the buffer pointed to by +.Fa buf . +The +.Fn writev +system call +performs the same action, but gathers the output data +from the +.Fa iovcnt +buffers specified by the members of the +.Fa iov +array: iov[0], iov[1], ..., iov[iovcnt\|-\|1]. +The +.Fn pwrite +and +.Fn pwritev +system calls +perform the same functions, but write to the specified position in +the file without modifying the file pointer. +.Pp +For +.Fn writev +and +.Fn pwritev , +the +.Fa iovec +structure is defined as: +.Pp +.Bd -literal -offset indent -compact +struct iovec { + void *iov_base; /* Base address. */ + size_t iov_len; /* Length. */ +}; +.Ed +.Pp +Each +.Fa iovec +entry specifies the base address and length of an area +in memory from which data should be written. +The +.Fn writev +system call +will always write a complete area before proceeding +to the next. +.Pp +On objects capable of seeking, the +.Fn write +starts at a position +given by the pointer associated with +.Fa d , +see +.Xr lseek 2 . +Upon return from +.Fn write , +the pointer is incremented by the number of bytes which were written. +.Pp +Objects that are not capable of seeking always write from the current +position. +The value of the pointer associated with such an object +is undefined. +.Pp +If the real user is not the super-user, then +.Fn write +clears the set-user-id bit on a file. +This prevents penetration of system security +by a user who +.Dq captures +a writable set-user-id file +owned by the super-user. +.Pp +When using non-blocking I/O on objects such as sockets that are subject +to flow control, +.Fn write +and +.Fn writev +may write fewer bytes than requested; +the return value must be noted, +and the remainder of the operation should be retried when possible. +.Sh RETURN VALUES +Upon successful completion the number of bytes which were written +is returned. +Otherwise a -1 is returned and the global variable +.Va errno +is set to indicate the error. +.Sh ERRORS +The +.Fn write , +.Fn writev , +.Fn pwrite +and +.Fn pwritev +system calls +will fail and the file pointer will remain unchanged if: +.Bl -tag -width Er +.It Bq Er EBADF +The +.Fa d +argument +is not a valid descriptor open for writing. +.It Bq Er EPIPE +An attempt is made to write to a pipe that is not open +for reading by any process. +.It Bq Er EPIPE +An attempt is made to write to a socket of type +.Dv SOCK_STREAM +that is not connected to a peer socket. +.It Bq Er EFBIG +An attempt was made to write a file that exceeds the process's +file size limit or the maximum file size. +.It Bq Er EFAULT +Part of +.Fa iov +or data to be written to the file +points outside the process's allocated address space. +.It Bq Er EINVAL +The pointer associated with +.Fa d +was negative. +.It Bq Er ENOSPC +There is no free space remaining on the file system +containing the file. +.It Bq Er EDQUOT +The user's quota of disk blocks on the file system +containing the file has been exhausted. +.It Bq Er EIO +An I/O error occurred while reading from or writing to the file system. +.It Bq Er EINTR +A signal interrupted the write before it could be completed. +.It Bq Er EAGAIN +The file was marked for non-blocking I/O, +and no data could be written immediately. +.It Bq Er EROFS +An attempt was made to write over a disk label area at the beginning +of a slice. +Use +.Xr disklabel 8 +.Fl W +to enable writing on the disk label area. +.It Bq Er EINVAL +The value +.Fa nbytes +is greater than +.Dv INT_MAX . +.El +.Pp +In addition, +.Fn writev +and +.Fn pwritev +may return one of the following errors: +.Bl -tag -width Er +.It Bq Er EDESTADDRREQ +The destination is no longer available when writing to a +.Ux +domain datagram socket on which +.Xr connect 2 +had been used to set a destination address. +.It Bq Er EINVAL +The +.Fa iovcnt +argument +was less than or equal to 0, or greater than +.Dv IOV_MAX . +.It Bq Er EINVAL +One of the +.Fa iov_len +values in the +.Fa iov +array was negative. +.It Bq Er EINVAL +The sum of the +.Fa iov_len +values in the +.Fa iov +array overflowed a 32-bit integer. +.It Bq Er ENOBUFS +The mbuf pool has been completely exhausted when writing to a socket. +.El +.Pp +The +.Fn pwrite +and +.Fn pwritev +system calls may also return the following errors: +.Bl -tag -width Er +.It Bq Er EINVAL +The +.Fa offset +value was negative. +.It Bq Er ESPIPE +The file descriptor is associated with a pipe, socket, or FIFO. +.El +.Sh SEE ALSO +.Xr fcntl 2 , +.Xr lseek 2 , +.Xr open 2 , +.Xr pipe 2 , +.Xr select 2 +.Sh STANDARDS +The +.Fn write +system call is expected to conform to +.St -p1003.1-90 . +The +.Fn writev +and +.Fn pwrite +system calls are expected to conform to +.St -xpg4.2 . +.Sh HISTORY +The +.Fn pwritev +system call appeared in +.Fx 6.0 . +The +.Fn pwrite +function appeared in +.At V.4 . +The +.Fn writev +system call appeared in +.Bx 4.2 . +The +.Fn write +function appeared in +.At v6 . |
