man3/aio_read.3

   1 .\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
   2 .\"
   3 .\" This is free documentation; you can redistribute it and/or
   4 .\" modify it under the terms of the GNU General Public License as
   5 .\" published by the Free Software Foundation; either version 2 of
   6 .\" the License, or (at your option) any later version.
   7 .\"
   8 .\" The GNU General Public License's references to "object code"
   9 .\" and "executables" are to be interpreted as the output of any
  10 .\" document formatting or typesetting system, including
  11 .\" intermediate and printed output.
  12 .\"
  13 .\" This manual is distributed in the hope that it will be useful,
  14 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 .\" GNU General Public License for more details.
  17 .\"
  18 .\" You should have received a copy of the GNU General Public
  19 .\" License along with this manual; if not, write to the Free
  20 .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
  21 .\" USA.
  22 .\"
  23 .TH AIO_READ 3 2003-11-14  "" "Linux Programmer's Manual"
  24 .SH NAME
  25 aio_read \- asynchronous read
  26 .SH SYNOPSIS
  27 .B "#include <aio.h>"
  28 .sp
  29 .BI "int aio_read(struct aiocb *" aiocbp );
  30 .sp
  31 Link with \fI\-lrt\fP.
  32 .SH DESCRIPTION
  33 The
  34 .BR aio_read ()
  35 function requests an asynchronous "n = read(fd, buf, count)"
  36 with fd, buf, count given by
  37 .IR aiocbp\->aio_fildes ,
  38 .IR aiocbp\->aio_buf ,
  39 .IR aiocbp\->aio_nbytes ,
  40 respectively.
  41 The return status n can be retrieved upon completion using
  42 .BR aio_return (3).
  43 .LP
  44 The data is read starting at the absolute file offset
  45 .IR aiocbp\->aio_offset ,
  46 regardless of the current file position.
  47 After this request,
  48 the value of the current file position is unspecified.
  49 .LP
  50 The "asynchronous" means that this call returns as soon as the
  51 request has been enqueued; the read may or may not have completed
  52 when the call returns.
  53 One tests for completion using
  54 .BR aio_error (3).
  55 .LP
  56 If
  57 .B _POSIX_PRIORITIZED_IO
  58 is defined, and this file supports it,
  59 then the asynchronous operation is submitted at a priority equal
  60 to that of the calling process minus
  61 .IR aiocbp\->aio_reqprio .
  62 .LP
  63 The field
  64 .I aiocbp\->aio_lio_opcode
  65 is ignored.
  66 .LP
  67 No data is read from a regular file beyond its maximum offset.
  68 .SH "RETURN VALUE"
  69 On success, 0 is returned.
  70 On error the request is not enqueued, \-1
  71 is returned, and
  72 .I errno
  73 is set appropriately.
  74 If an error is first detected later, it will
  75 be reported via
  76 .BR aio_return (3)
  77 (returns status \-1) and
  78 .BR aio_error (3)
  79 (error status whatever one would have gotten in
  80 .IR errno ,
  81 such as
  82 .BR EBADF ).
  83 .SH ERRORS
  84 .TP
  85 .B EAGAIN
  86 Out of resources.
  87 .TP
  88 .B EBADF
  89 .I aio_fildes
  90 is not a valid file descriptor open for reading.
  91 .TP
  92 .B EINVAL
  93 One or more of
  94 .IR aio_offset ,
  95 .IR aio_reqprio ,
  96 .I aio_nbytes
  97 are invalid.
  98 .TP
  99 .B ENOSYS
 100 This function is not supported.
 101 .TP
 102 .B EOVERFLOW
 103 The file is a regular file, we start reading before end-of-file
 104 and want at least one byte, but the starting position is past
 105 the maximum offset for this file.
 106 .SH "CONFORMING TO"
 107 POSIX.1-2001.
 108 .SH NOTES
 109 It is a good idea to zero out the control block before use.
 110 This control block must not be changed while the read operation
 111 is in progress.
 112 The buffer area being read into
 113 .\" or the control block of the operation
 114 must not be accessed during the operation or undefined results may
 115 occur.
 116 The memory areas involved must remain valid.
 117 .SH "SEE ALSO"
 118 .BR aio_cancel (3),
 119 .BR aio_error (3),
 120 .BR aio_fsync (3),
 121 .BR aio_return (3),
 122 .BR aio_suspend (3),
 123 .BR aio_write (3)