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155 lines
3.9 KiB
Groff
155 lines
3.9 KiB
Groff
.\" Copyright (c) 2016, EMC / Isilon Storage Division
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
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.\" IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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.\" THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR
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.\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd May 9, 2016
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.Dt FOPENCOOKIE 3
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.Os
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.Sh NAME
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.Nm fopencookie
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.Nd open a stream
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft typedef ssize_t
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.Fn (*cookie_read_function_t) "void *cookie" "char *buf" "size_t size"
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.Ft typedef ssize_t
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.Fn (*cookie_write_function_t) "void *cookie" "const char *buf" "size_t size"
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.Ft typedef int
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.Fn (*cookie_seek_function_t) "void *cookie" "off64_t *offset" "int whence"
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.Ft typedef int
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.Fn (*cookie_close_function_t) "void *cookie"
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.Bd -literal
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typedef struct {
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cookie_read_function_t *read;
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cookie_write_function_t *write;
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cookie_seek_function_t *seek;
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cookie_close_function_t *close;
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} cookie_io_functions_t;
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.Ed
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.Ft FILE *
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.Fn fopencookie "void *cookie" "const char *mode" "cookie_io_functions_t io_funcs"
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.Sh DESCRIPTION
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The
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.Nm
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function
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associates a stream with up to four
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.Dq Tn I/O No functions .
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These
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.Tn I/O
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functions will be used to read, write, seek and
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close the new stream.
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.Pp
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In general, omitting a function means that any attempt to perform the
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associated operation on the resulting stream will fail.
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If the write function is omitted, data written to the stream is discarded.
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If the close function is omitted, closing the stream will flush
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any buffered output and then succeed.
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.Pp
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The calling conventions of
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.Fa read ,
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.Fa write ,
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and
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.Fa close
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must match those, respectively, of
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.Xr read 2 ,
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.Xr write 2 ,
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and
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.Xr close 2
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with the single exception that they are passed the
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.Fa cookie
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argument specified to
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.Nm
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in place of the traditional file descriptor argument.
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The
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.Fa seek
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function updates the current stream offset using
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.Fa *offset
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and
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.Fa whence .
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If
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.Fa *offset
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is non-NULL, it updates
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.Fa *offset
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with the current stream offset.
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.Pp
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.Nm
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is implemented as a thin shim around the
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.Xr funopen 3
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interface.
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Limitations, possibilities, and requirements of that interface apply to
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.Nm .
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.Sh RETURN VALUES
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Upon successful completion,
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.Nm
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returns a
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.Dv FILE
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pointer.
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Otherwise,
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.Dv NULL
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is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EINVAL
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A bogus
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.Fa mode
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was provided to
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.Nm .
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.It Bq Er ENOMEM
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The
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.Nm
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function
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may fail and set
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.Va errno
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for any of the errors
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specified for the
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.Xr malloc 3
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routine.
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.El
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.Sh SEE ALSO
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.Xr fcntl 2 ,
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.Xr open 2 ,
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.Xr fclose 3 ,
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.Xr fopen 3 ,
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.Xr fseek 3 ,
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.Xr funopen 3
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.Sh HISTORY
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The
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.Fn funopen
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functions first appeared in
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.Bx 4.4 .
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The
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.Nm
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function first appeared in
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.Fx 11 .
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.Sh BUGS
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The
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.Nm
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function is a nonstandard glibc extension and may not be portable to systems
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other than
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.Fx
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and Linux.
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