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https://issues.apache.org/jira/browse/HADOOP-8569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13415584#comment-13415584
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Andy Isaacson commented on HADOOP-8569:
---------------------------------------
The downside to defining {{_GNU_SOURCE}} everywhere -- in both code that is
known to need it, and in code that is intended to be portable -- is that it
makes it very easy to accidentally break compilation on non-GNU platforms by
unintentionally changing code from "portable" to "gnu-specific". Suppose we
have a project with {{foo-linux.c}} containing nonportable code, and
{{generic.c}} containing POSIX portable code. If I define {{_GNU_SOURCE}} in
{{CFLAGS}} then unintentionally adding a call to {{sync_file_range}} to
{{generic.c}} will silently work on Linux, and won't break the build until you
try building on Darwin or Solaris or whatever.
If instead the project puts {{#define _GNU_SOURCE}} at the top of files
intended to be platform-specific, then such portability breakage will be
noticed immediately.
The argument doesn't extend to LFS support -- it's entirely reasonable to use
64-bit-{{off_t}} everywhere including Linux-32.
{code}
+# note: can't enable -D_FILE_OFFSET_BITS=64: see MAPREDUCE-4258
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_REENTRANT -D_GNU_SOURCE")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_LARGEFILE_SOURCE")
{code}
If we don't have FILE_OFFSET_BITS=64, then shouldn't we also leave out
LARGEFILE_SOURCE? (This is a serious question, I don't know how those two
defines interact, I just vaguely remember that there's a complicated rule about
how they should be used.)
In summary -- I'd slightly prefer to limit the GNU_SOURCE to a {{#define}} in
the files that we intend to be Linux-specific. The rest of this patch is good
though, cleaning up the LFS defines and adding that comment about
MAPREDUCE-4258.
> 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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