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Diffstat (limited to 'lib/libc/sys/read.2')
| -rw-r--r-- | lib/libc/sys/read.2 | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/lib/libc/sys/read.2 b/lib/libc/sys/read.2 new file mode 100644 index 0000000..b94341a --- /dev/null +++ b/lib/libc/sys/read.2 @@ -0,0 +1,189 @@ +.\" 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. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 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. +.\" +.\" @(#)read.2 8.4 (Berkeley) 2/26/94 +.\" +.Dd February 26, 1994 +.Dt READ 2 +.Os BSD 4 +.Sh NAME +.Nm read , +.Nm readv +.Nd read input +.Sh SYNOPSIS +.Fd #include <sys/types.h> +.Fd #include <sys/uio.h> +.Fd #include <unistd.h> +.Ft ssize_t +.Fn read "int d" "void *buf" "size_t nbytes" +.Ft ssize_t +.Fn readv "int d" "const struct iovec *iov" "int iovcnt" +.Sh DESCRIPTION +.Fn Read +attempts to read +.Fa nbytes +of data from the object referenced by the descriptor +.Fa d +into the buffer pointed to by +.Fa buf . +.Fn Readv +performs the same action, but scatters the input data +into the +.Fa iovcnt +buffers specified by the members of the +.Fa iov +array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1]. +.Pp +For +.Fn readv , +the +.Fa iovec +structure is defined as: +.Pp +.Bd -literal -offset indent -compact +struct iovec { + void *iov_base; + size_t iov_len; +}; +.Ed +.Pp +Each +.Fa iovec +entry specifies the base address and length of an area +in memory where data should be placed. +.Fn Readv +will always fill an area completely before proceeding +to the next. +.Pp +On objects capable of seeking, the +.Fn read +starts at a position +given by the pointer associated with +.Fa d +(see +.Xr lseek 2 ) . +Upon return from +.Fn read , +the pointer is incremented by the number of bytes actually read. +.Pp +Objects that are not capable of seeking always read from the current +position. The value of the pointer associated with such an +object is undefined. +.Pp +Upon successful completion, +.Fn read +and +.Fn readv +return the number of bytes actually read and placed in the buffer. +The system guarantees to read the number of bytes requested if +the descriptor references a normal file that has that many bytes left +before the end-of-file, but in no other case. +.Pp +.Sh RETURN VALUES +If successful, the +number of bytes actually read is returned. Upon reading end-of-file, +zero is returned. +Otherwise, a -1 is returned and the global variable +.Va errno +is set to indicate the error. +.Sh ERRORS +.Fn Read +and +.Fn readv +will succeed unless: +.Bl -tag -width Er +.It Bq Er EBADF +.Fa D +is not a valid file or socket descriptor open for reading. +.It Bq Er EFAULT +.Fa Buf +points outside the allocated address space. +.It Bq Er EIO +An I/O error occurred while reading from the file system. +.It Bq Er EINTR +A read from a slow device was interrupted before +any data arrived by the delivery of a signal. +.It Bq Er EINVAL +The pointer associated with +.Fa d +was negative. +.It Bq Er EAGAIN +The file was marked for non-blocking I/O, +and no data were ready to be read. +.El +.Pp +In addition, +.Fn readv +may return one of the following errors: +.Bl -tag -width Er +.It Bq Er EINVAL +.Fa Iovcnt +was less than or equal to 0, or greater than 16. +.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 EFAULT +Part of the +.Fa iov +points outside the process's allocated address space. +.El +.Sh SEE ALSO +.Xr dup 2 , +.Xr fcntl 2 , +.Xr open 2 , +.Xr pipe 2 , +.Xr select 2 , +.Xr socket 2 , +.Xr socketpair 2 +.Sh STANDARDS +.Fn Read +is expected to conform to IEEE Std 1003.1-1988 +.Pq Dq Tn POSIX . +.Sh HISTORY +The +.Fn readv +function call +appeared in +.Bx 4.2 . +A +.Nm read +function call +appeared in +Version 6 AT&T UNIX. |
