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Annotation of 43BSDReno/lib/libc/sys/read.2, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)read.2      6.6 (Berkeley) 5/23/86
        !             6: .\"
        !             7: .TH READ 2 "May 23, 1986"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: read, readv \- read input
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: .ft B
        !            14: cc = read(d, buf, nbytes)
        !            15: int cc, d;
        !            16: char *buf;
        !            17: int nbytes;
        !            18: .PP
        !            19: .ft B
        !            20: #include <sys/types.h>
        !            21: #include <sys/uio.h>
        !            22: .PP
        !            23: .ft B
        !            24: cc = readv(d, iov, iovcnt)
        !            25: int cc, d;
        !            26: struct iovec *iov;
        !            27: int iovcnt;
        !            28: .fi
        !            29: .SH DESCRIPTION
        !            30: .I Read
        !            31: attempts to read
        !            32: .I nbytes
        !            33: of data from the object referenced by the descriptor
        !            34: .I d
        !            35: into the buffer pointed to by
        !            36: .IR buf .
        !            37: .I Readv
        !            38: performs the same action, but scatters the input data
        !            39: into the 
        !            40: .I iovcnt
        !            41: buffers specified by the members of the
        !            42: .I iov
        !            43: array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
        !            44: .PP
        !            45: For 
        !            46: .IR readv ,
        !            47: the 
        !            48: .I iovec
        !            49: structure is defined as
        !            50: .PP
        !            51: .nf
        !            52: .RS
        !            53: .DT
        !            54: struct iovec {
        !            55:        caddr_t iov_base;
        !            56:        int     iov_len;
        !            57: };
        !            58: .RE
        !            59: .fi
        !            60: .PP
        !            61: Each 
        !            62: .I iovec
        !            63: entry specifies the base address and length of an area
        !            64: in memory where data should be placed. 
        !            65: .I Readv
        !            66: will always fill an area completely before proceeding
        !            67: to the next.
        !            68: .PP
        !            69: On objects capable of seeking, the
        !            70: .I read
        !            71: starts at a position
        !            72: given by the pointer associated with
        !            73: .IR d 
        !            74: (see
        !            75: .IR lseek (2)).
        !            76: Upon return from
        !            77: .IR read ,
        !            78: the pointer is incremented by the number of bytes actually read.
        !            79: .PP
        !            80: Objects that are not capable of seeking always read from the current
        !            81: position.  The value of the pointer associated with such an
        !            82: object is undefined.
        !            83: .PP
        !            84: Upon successful completion,
        !            85: .I read
        !            86: and
        !            87: .I readv
        !            88: return the number of bytes actually read and placed in the buffer.
        !            89: The system guarantees to read the number of bytes requested if
        !            90: the descriptor references a normal file that has that many bytes left
        !            91: before the end-of-file, but in no other case.
        !            92: .PP
        !            93: If the returned value is 0, then
        !            94: end-of-file has been reached.
        !            95: .SH "RETURN VALUE
        !            96: If successful, the
        !            97: number of bytes actually read is returned.
        !            98: Otherwise, a \-1 is returned and the global variable
        !            99: .I errno
        !           100: is set to indicate the error.
        !           101: .SH "ERRORS
        !           102: .I Read
        !           103: and
        !           104: .I readv
        !           105: will fail if one or more of the following are true:
        !           106: .TP 15
        !           107: [EBADF]
        !           108: \fID\fP is not a valid file or socket descriptor open for reading.
        !           109: .TP 15
        !           110: [EFAULT]
        !           111: \fIBuf\fP points outside the allocated address space.
        !           112: .TP 15
        !           113: [EIO]
        !           114: An I/O error occurred while reading from the file system.
        !           115: .TP 15
        !           116: [EINTR]
        !           117: A read from a slow device was interrupted before
        !           118: any data arrived by the delivery of a signal.
        !           119: .TP 15
        !           120: [EINVAL]
        !           121: The pointer associated with
        !           122: .I d
        !           123: was negative.
        !           124: .TP 15
        !           125: [EWOULDBLOCK]
        !           126: The file was marked for non-blocking I/O,
        !           127: and no data were ready to be read.
        !           128: .PP
        !           129: In addition, 
        !           130: .I readv
        !           131: may return one of the following errors:
        !           132: .TP 15
        !           133: [EINVAL]
        !           134: .I Iovcnt
        !           135: was less than or equal to 0, or greater than 16.
        !           136: .TP 15
        !           137: [EINVAL]
        !           138: One of the
        !           139: .I iov_len
        !           140: values in the
        !           141: .I iov
        !           142: array was negative.
        !           143: .TP 15
        !           144: [EINVAL]
        !           145: The sum of the
        !           146: .I iov_len
        !           147: values in the
        !           148: .I iov
        !           149: array overflowed a 32-bit integer.
        !           150: .TP 15
        !           151: [EFAULT]
        !           152: Part of the \fIiov\fP points outside the process's allocated address space.
        !           153: .SH "SEE ALSO"
        !           154: dup(2), fcntl(2), open(2), pipe(2), select(2), socket(2), socketpair(2)

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