man3/aio_read.3

   1 .\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
   2 .\"
   3 .\" SPDX-License-Identifier: GPL-2.0-or-later
   4 .\"
   5 .TH AIO_READ 3 2021-03-22  "" "Linux Programmer's Manual"
   6 .SH NAME
   7 aio_read \- asynchronous read
   8 .SH LIBRARY
   9 Real-time library
  10 .RI ( librt ", " \-lrt )
  11 .SH SYNOPSIS
  12 .nf
  13 .B "#include <aio.h>"
  14 .PP
  15 .BI "int aio_read(struct aiocb *" aiocbp );
  16 .fi
  17 .SH DESCRIPTION
  18 The
  19 .BR aio_read ()
  20 function queues the I/O request described by the buffer pointed to by
  21 .IR aiocbp .
  22 This function is the asynchronous analog of
  23 .BR read (2).
  24 The arguments of the call
  25 .PP
  26     read(fd, buf, count)
  27 .PP
  28 correspond (in order) to the fields
  29 .IR aio_fildes ,
  30 .IR aio_buf ,
  31 and
  32 .IR aio_nbytes
  33 of the structure pointed to by
  34 .IR aiocbp .
  35 (See
  36 .BR aio (7)
  37 for a description of the
  38 .I aiocb
  39 structure.)
  40 .PP
  41 The data is read starting at the absolute position
  42 .IR aiocbp\->aio_offset ,
  43 regardless of the file offset.
  44 After the call,
  45 the value of the file offset is unspecified.
  46 .PP
  47 The "asynchronous" means that this call returns as soon as the
  48 request has been enqueued; the read may or may not have completed
  49 when the call returns.
  50 One tests for completion using
  51 .BR aio_error (3).
  52 The return status of a completed I/O operation can be obtained by
  53 .BR aio_return (3).
  54 Asynchronous notification of I/O completion can be obtained by setting
  55 .IR aiocbp\->aio_sigevent
  56 appropriately; see
  57 .BR sigevent (7)
  58 for details.
  59 .PP
  60 If
  61 .B _POSIX_PRIORITIZED_IO
  62 is defined, and this file supports it,
  63 then the asynchronous operation is submitted at a priority equal
  64 to that of the calling process minus
  65 .IR aiocbp\->aio_reqprio .
  66 .PP
  67 The field
  68 .I aiocbp\->aio_lio_opcode
  69 is ignored.
  70 .PP
  71 No data is read from a regular file beyond its maximum offset.
  72 .SH RETURN VALUE
  73 On success, 0 is returned.
  74 On error, the request is not enqueued, \-1
  75 is returned, and
  76 .I errno
  77 is set to indicate the error.
  78 If an error is detected only later, it will
  79 be reported via
  80 .BR aio_return (3)
  81 (returns status \-1) and
  82 .BR aio_error (3)
  83 (error status\(emwhatever one would have gotten in
  84 .IR errno ,
  85 such as
  86 .BR EBADF ).
  87 .SH ERRORS
  88 .TP
  89 .B EAGAIN
  90 Out of resources.
  91 .TP
  92 .B EBADF
  93 .I aio_fildes
  94 is not a valid file descriptor open for reading.
  95 .TP
  96 .B EINVAL
  97 One or more of
  98 .IR aio_offset ,
  99 .IR aio_reqprio ,
 100 or
 101 .I aio_nbytes
 102 are invalid.
 103 .TP
 104 .B ENOSYS
 105 .BR aio_read ()
 106 is not implemented.
 107 .TP
 108 .B EOVERFLOW
 109 The file is a regular file, we start reading before end-of-file
 110 and want at least one byte, but the starting position is past
 111 the maximum offset for this file.
 112 .SH VERSIONS
 113 The
 114 .BR aio_read ()
 115 function is available since glibc 2.1.
 116 .SH ATTRIBUTES
 117 For an explanation of the terms used in this section, see
 118 .BR attributes (7).
 119 .ad l
 120 .nh
 121 .TS
 122 allbox;
 123 lbx lb lb
 124 l l l.
 125 Interface       Attribute       Value
 126 T{
 127 .BR aio_read ()
 128 T}      Thread safety   MT-Safe
 129 .TE
 130 .hy
 131 .ad
 132 .sp 1
 133 .SH CONFORMING TO
 134 POSIX.1-2001, POSIX.1-2008.
 135 .SH NOTES
 136 It is a good idea to zero out the control block before use.
 137 The control block must not be changed while the read operation
 138 is in progress.
 139 The buffer area being read into
 140 .\" or the control block of the operation
 141 must not be accessed during the operation or undefined results may occur.
 142 The memory areas involved must remain valid.
 143 .PP
 144 Simultaneous I/O operations specifying the same
 145 .I aiocb
 146 structure produce undefined results.
 147 .SH EXAMPLES
 148 See
 149 .BR aio (7).
 150 .SH SEE ALSO
 151 .BR aio_cancel (3),
 152 .BR aio_error (3),
 153 .BR aio_fsync (3),
 154 .BR aio_return (3),
 155 .BR aio_suspend (3),
 156 .BR aio_write (3),
 157 .BR lio_listio (3),
 158 .BR aio (7)