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 $
  26 .\"
  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 .Fo aio_write
  39 .Fa "struct aiocb *aiocbp"
  40 .Fc
  41 .Sh DESCRIPTION
  42 The
  43 .Fn aio_write
  44 system call allows the calling process to write
  45 .Fa aiocbp->aio_nbytes
  46 from the buffer pointed to by
  47 .Fa aiocbp->aio_buf
  48 to the descriptor
  49 .Fa aiocbp->aio_fildes .
  50 The call returns immediately after the write request has been enqueued
  51 to the descriptor; the write may or may not have completed at the time
  52 the call returns.  If the request could not be enqueued, generally due
  53 to invalid arguments, the call returns without having enqueued the
  54 request.
  55 .Pp
  56 If
  57 .Dv O_APPEND
  58 is set for
  59 .Fa aiocbp->aio_fildes ,
  60 .Fn aio_write
  61 operations append to the file in the same order as the calls were
  62 made.  If
  63 .Dv O_APPEND
  64 is not set for the file descriptor, the write operation will occur at
  65 the absolute position from the beginning of the file plus
  66 .Fa aiocbp->aio_offset .
  67 .Pp
  68 If
  69 .Dv _POSIX_PRIORITIZED_IO
  70 is defined, and the descriptor supports it, then the enqueued
  71 operation is submitted at a priority equal to that of the calling
  72 process minus
  73 .Fa aiocbp->aio_reqprio .
  74 .Pp
  75 The
  76 .Fa aiocbp
  77 pointer may be subsequently used as an argument to
  78 .Fn aio_return
  79 and
  80 .Fn aio_error
  81 in order to determine return or error status for the enqueued operation
  82 while it is in progress.
  83 .Pp
  84 If the request is successfully enqueued, the value of
  85 .Fa aiocbp->aio_offset
  86 can be modified during the request as context, so this value must not
  87 be referenced after the request is enqueued.
  88 .Sh RESTRICTIONS
  89 The Asynchronous I/O Control Block structure pointed to by
  90 .Fa aiocbp
  91 and the buffer that the
  92 .Fa aiocbp->aio_buf
  93 member of that structure references must remain valid until the
  94 operation has completed.  For this reason, use of auto (stack) variables
  95 for these objects is discouraged.
  96 .Pp
  97 The asynchronous I/O control buffer
  98 .Fa aiocbp
  99 should be zeroed before the
 100 .Fn aio_write
 101 system call to avoid passing bogus context information to the kernel.
 102 .Pp
 103 Modifications of the Asynchronous I/O Control Block structure or the
 104 buffer contents after the request has been enqueued, but before the
 105 request has completed, are not allowed.
 106 .Pp
 107 If the file offset in
 108 .Fa aiocbp->aio_offset
 109 is past the offset maximum  for
 110 .Fa aiocbp->aio_fildes ,
 111 no I/O will occur.
 112 .Sh RETURN VALUES
 113 .Rv -std aio_write
 114 .Sh ERRORS
 115 The
 116 .Fn aio_write
 117 system call will fail if:
 118 .Bl -tag -width Er
 119 .\" ==========
 120 .It Bq Er EAGAIN
 121 Due to system resource limitations,
 122 the request was not queued.
 123 .\" ==========
 124 .It Bq Er ENOSYS
 125 The
 126 .Fn aio_write
 127 system call is not supported.
 128 .El
 129 .Pp
 130 The following conditions may be synchronously detected when the
 131 .Fn aio_write
 132 system call is made, or asynchronously, at any time thereafter.  If they
 133 are detected at call time,
 134 .Fn aio_write
 135 returns -1 and sets
 136 .Va errno
 137 appropriately; otherwise the
 138 .Fn aio_return
 139 system call must be called, and will return -1, and
 140 .Fn aio_error
 141 must be called to determine the actual value that would have been
 142 returned in
 143 .Va errno .
 144 .Pp
 145 .Bl -tag -width Er
 146 .\" ==========
 147 .It Bq Er EBADF
 148 The
 149 .Fa aiocbp->aio_fildes
 150 argument
 151 is invalid, or is not opened for writing.
 152 .\" ==========
 153 .It Bq Er EINVAL
 154 The offset
 155 .Fa aiocbp->aio_offset
 156 is not valid, the priority specified by
 157 .Fa aiocbp->aio_reqprio
 158 is not a valid priority, or the number of bytes specified by
 159 .Fa aiocbp->aio_nbytes
 160 is not valid.
 161 .El
 162 .Pp
 163 If the request is successfully enqueued, but subsequently canceled
 164 or an error occurs, the value returned by the
 165 .Fn aio_return
 166 system call is per the
 167 .Xr write 2
 168 system call, and the value returned by the
 169 .Fn aio_error
 170 system call is either one of the error returns from the
 171 .Xr write 2
 172 system call, or one of:
 173 .Bl -tag -width Er
 174 .\" ==========
 175 .It Bq Er EBADF
 176 The
 177 .Fa aiocbp->aio_fildes
 178 argument
 179 is invalid for writing.
 180 .\" ==========
 181 .It Bq Er ECANCELED
 182 The request was explicitly canceled via a call to
 183 .Fn aio_cancel .
 184 .\" ==========
 185 .It Bq Er EINVAL
 186 The offset
 187 .Fa aiocbp->aio_offset
 188 would be invalid.
 189 .El
 190 .Sh SEE ALSO
 191 .Xr aio_cancel 2 ,
 192 .Xr aio_error 2 ,
 193 .Xr aio_return 2 ,
 194 .Xr aio_suspend 2 ,
 195 .Xr aio 4
 196 .Sh STANDARDS
 197 The
 198 .Fn aio_write
 199 system call
 200 is expected to conform to the
 201 .St -p1003.1
 202 standard.
 203 .Sh HISTORY
 204 The
 205 .Fn aio_write
 206 system call first appeared in
 207 .Fx 3.0 .
 208 .Sh AUTHORS
 209 This manual page was written by
 210 .An Wes Peters Aq wes@softweyr.com .
 211 .Sh BUGS
 212 Invalid information in
 213 .Fa aiocbp->_aiocb_private
 214 may confuse the kernel.