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https://issues.apache.org/jira/browse/HADOOP-8569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13415619#comment-13415619
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Colin Patrick McCabe commented on HADOOP-8569:
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_GNU_SOURCE was defined previously in most (if not all) of our native projects.
After I did the CMake conversion, the fact that it wasn't defined in the
CMakeLists.txt was a bug, not a feature. That's what I'm trying to fix here.
I realize that it's tempting to assume that code that you write without
_GNU_SOURCE defined will automatically be portable. However, this is *NOT
TRUE*. For example, even without _GNU_SOURCE defined, you still get the
non-POSIX definition of strerror_r out of glibc.
The only valid way to make sure your code is portable is to build and test it
on multiple platforms. Any other strategy is just a waste of time. Defining
GNU_SOURCE is similar to setting the correct DOCTYPE in your HTML file. It
tells the browser (or compiler in this case) to turn off "quirks mode" and give
you the real deal.
I don't think the CheckFunctionExists stuff in the CMakeLists.txt will work
consistently without _GNU_SOURCE defined.
There are better ways to improve our portability. For example, we should
probably have some OpenBSD jenkins build slaves. But let's not waste our time
messing with macros. It really adds nothing but inconvenience.
bq. If we don't have FILE_OFFSET_BITS=64, then shouldn't we also leave out
LARGEFILE_SOURCE?
_LARGEFILE_SOURCE exposes fseeko and ftello. _FILE_OFFSET_BITS changes the
default off_t type to be 64 bits. Basically _LARGEFILE_SOURCE is something you
need to define in addition to _FILE_OFFSET_BITS, but the two things do
different things.
> CMakeLists.txt: define _GNU_SOURCE and _LARGEFILE_SOURCE
> --------------------------------------------------------
>
> Key: HADOOP-8569
> URL: https://issues.apache.org/jira/browse/HADOOP-8569
> Project: Hadoop Common
> Issue Type: Bug
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HADOOP-8569.001.patch
>
>
> In the native code, we should define _GNU_SOURCE and _LARGEFILE_SOURCE so
> that all of the functions on Linux are available.
> _LARGEFILE enables fseeko and ftello; _GNU_SOURCE enables a variety of
> Linux-specific functions from glibc, including sync_file_range.
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