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manual: Document the O_TMPFILE flag

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Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
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Florian Weimer 2017-11-04 00:57:19 +01:00
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@ -1,3 +1,7 @@
2017-11-04 Florian Weimer <fweimer@redhat.com>
* manual/llio.texi (Open-time Flags): Document O_TMPFILE.
2017-11-03 Joseph Myers <joseph@codesourcery.com>
* math/math.h [__HAVE_DISTINCT_FLOAT16

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manual/llio.texi
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@ -3478,6 +3478,34 @@ If set, the file will be created if it doesn't already exist.
If both @code{O_CREAT} and @code{O_EXCL} are set, then @code{open} fails
if the specified file already exists. This is guaranteed to never
clobber an existing file.
The @code{O_EXCL} flag has a special meaning in combination with
@code{O_TMPFILE}; see below.
@end deftypevr
@deftypevr Macro int O_TMPFILE
@standards{GNU, fcntl.h}
If this flag is specified, functions in the @code{open} family create an
unnamed temporary file. In this case, the pathname argument to the
@code{open} family of functions (@pxref{Opening and Closing Files}) is
interpreted as the directory in which the temporary file is created
(thus determining the file system which provides the storage for the
file). The @code{O_TMPFILE} flag must be combined with @code{O_WRONLY}
or @code{O_RDWR}, and the @var{mode} argument is required.
The temporary file can later be given a name using @code{linkat},
turning it into a regular file. This allows the atomic creation of a
file with the specific file attributes (mode and extended attributes)
and file contents. If, for security reasons, it is not desirable that a
name can be given to the file, the @code{O_EXCL} flag can be specified
along with @code{O_TMPFILE}.
Not all kernels support this open flag. If this flag is unsupported, an
attempt to create an unnamed temporary file fails with an error of
@code{EINVAL}. If the underlying file system does not support the
@code{O_TMPFILE} flag, an @code{EOPNOTSUPP} error is the result.
The @code{O_TMPFILE} flag is a GNU extension.
@end deftypevr
@deftypevr Macro int O_NONBLOCK