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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 September 18, 2008

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.

157 .\" ==========

158 .It Bq Er EINVAL

159 The priority specified by

160 .Fa aiocbp->aio_reqprio

161 is not a valid priority.

162 .\" ==========

163 .It Bq Er EINVAL

164 The number of bytes specified by

165 .Fa aiocbp->aio_nbytes

166 is not valid.

167 .\" ==========

168 .It Bq Er EINVAL

169 The constant in

170 .Fa aiocbp->aio_sigevent.sigev_notify

171 is set to SIGEV_THREAD (SIGEV_THREAD is not supported).

172 .El

173 .Pp

174 If the request is successfully enqueued, but subsequently canceled

175 or an error occurs, the value returned by the

176 .Fn aio_return

177 system call is per the

178 .Xr write 2

179 system call, and the value returned by the

180 .Fn aio_error

181 system call is either one of the error returns from the

182 .Xr write 2

183 system call, or one of:

184 .Bl -tag -width Er

185 .\" ==========

186 .It Bq Er EBADF

187 The

188 .Fa aiocbp->aio_fildes

189 argument

190 is invalid for writing.

191 .\" ==========

192 .It Bq Er ECANCELED

193 The request was explicitly canceled via a call to

194 .Fn aio_cancel .

195 .El

196 .Sh SEE ALSO

197 .Xr aio_cancel 2 ,

198 .Xr aio_error 2 ,

199 .Xr aio_return 2 ,

200 .Xr aio_suspend 2 ,

201 .Xr aio 4

202 .Sh STANDARDS

203 The

204 .Fn aio_write

205 system call

206 is expected to conform to the

207 .St -p1003.1

208 standard.

209 .Sh HISTORY

210 The

211 .Fn aio_write

212 system call first appeared in

213 .Fx 3.0 .

214 .Sh AUTHORS

215 This manual page was written by

216 .An Wes Peters Aq wes@softweyr.com .

217 .Sh BUGS

218 Invalid information in

219 .Fa aiocbp->_aiocb_private

220 may confuse the kernel.