bsd/man/man2/aio_write.2

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  25 .\" $FreeBSD: src/lib/libc/sys/aio_write.2,v 1.16 2003/01/13 10:37:11 tjr Exp $
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  27 .Dd June 2, 1999
  28 .Dt AIO_WRITE 2
  29 .Os
  30 .Sh NAME
  31 .Nm aio_write
  32 .Nd asynchronous write to a file (REALTIME)
  33 .Sh LIBRARY
  34 .Lb libc
  35 .Sh SYNOPSIS
  36 .In aio.h
  37 .Ft int
  38 .Fn aio_write "struct aiocb *iocb"
  39 .Sh DESCRIPTION
  40 The
  41 .Fn aio_write
  42 system call allows the calling process to write
  43 .Fa iocb->aio_nbytes
  44 from the buffer pointed to by
  45 .Fa iocb->aio_buf
  46 to the descriptor
  47 .Fa iocb->aio_fildes .
  48 The call returns immediately after the write request has been enqueued
  49 to the descriptor; the write may or may not have completed at the time
  50 the call returns.  If the request could not be enqueued, generally due
  51 to invalid arguments, the call returns without having enqueued the
  52 request.
  53 .Pp
  54 If
  55 .Dv O_APPEND
  56 is set for
  57 .Fa iocb->aio_fildes ,
  58 .Fn aio_write
  59 operations append to the file in the same order as the calls were
  60 made.  If
  61 .Dv O_APPEND
  62 is not set for the file descriptor, the write operation will occur at
  63 the absolute position from the beginning of the file plus
  64 .Fa iocb->aio_offset .
  65 .Pp
  66 If
  67 .Dv _POSIX_PRIORITIZED_IO
  68 is defined, and the descriptor supports it, then the enqueued
  69 operation is submitted at a priority equal to that of the calling
  70 process minus
  71 .Fa iocb->aio_reqprio .
  72 .Pp
  73 The
  74 .Fa iocb
  75 pointer may be subsequently used as an argument to
  76 .Fn aio_return
  77 and
  78 .Fn aio_error
  79 in order to determine return or error status for the enqueued operation
  80 while it is in progress.
  81 .Pp
  82 If the request is successfully enqueued, the value of
  83 .Fa iocb->aio_offset
  84 can be modified during the request as context, so this value must not
  85 be referenced after the request is enqueued.
  86 .Sh RESTRICTIONS
  87 The Asynchronous I/O Control Block structure pointed to by
  88 .Fa iocb
  89 and the buffer that the
  90 .Fa iocb->aio_buf
  91 member of that structure references must remain valid until the
  92 operation has completed.  For this reason, use of auto (stack) variables
  93 for these objects is discouraged.
  94 .Pp
  95 The asynchronous I/O control buffer
  96 .Fa iocb
  97 should be zeroed before the
  98 .Fn aio_write
  99 system call to avoid passing bogus context information to the kernel.
 100 .Pp
 101 Modifications of the Asynchronous I/O Control Block structure or the
 102 buffer contents after the request has been enqueued, but before the
 103 request has completed, are not allowed.
 104 .Pp
 105 If the file offset in
 106 .Fa iocb->aio_offset
 107 is past the offset maximum  for
 108 .Fa iocb->aio_fildes ,
 109 no I/O will occur.
 110 .Sh RETURN VALUES
 111 .Rv -std aio_write
 112 .Sh ERRORS
 113 The
 114 .Fn aio_write
 115 system call will fail if:
 116 .Bl -tag -width Er
 117 .It Bq Er EAGAIN
 118 The request was not queued because of system resource limitations.
 119 .It Bq Er ENOSYS
 120 The
 121 .Fn aio_write
 122 system call is not supported.
 123 .El
 124 .Pp
 125 The following conditions may be synchronously detected when the
 126 .Fn aio_write
 127 system call is made, or asynchronously, at any time thereafter.  If they
 128 are detected at call time,
 129 .Fn aio_write
 130 returns -1 and sets
 131 .Va errno
 132 appropriately; otherwise the
 133 .Fn aio_return
 134 system call must be called, and will return -1, and
 135 .Fn aio_error
 136 must be called to determine the actual value that would have been
 137 returned in
 138 .Va errno .
 139 .Pp
 140 .Bl -tag -width Er
 141 .It Bq Er EBADF
 142 The
 143 .Fa iocb->aio_fildes
 144 argument
 145 is invalid, or is not opened for writing.
 146 .It Bq Er EINVAL
 147 The offset
 148 .Fa iocb->aio_offset
 149 is not valid, the priority specified by
 150 .Fa iocb->aio_reqprio
 151 is not a valid priority, or the number of bytes specified by
 152 .Fa iocb->aio_nbytes
 153 is not valid.
 154 .El
 155 .Pp
 156 If the request is successfully enqueued, but subsequently canceled
 157 or an error occurs, the value returned by the
 158 .Fn aio_return
 159 system call is per the
 160 .Xr write 2
 161 system call, and the value returned by the
 162 .Fn aio_error
 163 system call is either one of the error returns from the
 164 .Xr write 2
 165 system call, or one of:
 166 .Bl -tag -width Er
 167 .It Bq Er EBADF
 168 The
 169 .Fa iocb->aio_fildes
 170 argument
 171 is invalid for writing.
 172 .It Bq Er ECANCELED
 173 The request was explicitly canceled via a call to
 174 .Fn aio_cancel .
 175 .It Bq Er EINVAL
 176 The offset
 177 .Fa iocb->aio_offset
 178 would be invalid.
 179 .El
 180 .Sh SEE ALSO
 181 .Xr aio_cancel 2 ,
 182 .Xr aio_error 2 ,
 183 .Xr aio_return 2 ,
 184 .Xr aio_suspend 2 ,
 185 .Xr aio 4
 186 .Sh STANDARDS
 187 The
 188 .Fn aio_write
 189 system call
 190 is expected to conform to the
 191 .St -p1003.1
 192 standard.
 193 .Sh HISTORY
 194 The
 195 .Fn aio_write
 196 system call first appeared in
 197 .Fx 3.0 .
 198 .Sh AUTHORS
 199 This manual page was written by
 200 .An Wes Peters Aq wes@softweyr.com .
 201 .Sh BUGS
 202 Invalid information in
 203 .Fa iocb->_aiocb_private
 204 may confuse the kernel.