Proposal for adding O_DIRECT support into JDK 9

[Volker Simonis]

On Thu, Sep 7, 2017 at 8:38 PM, Brian Burkhalter
<brian.burkhalter at oracle.com> wrote:
> Hi Lucy,
>
> On Sep 6, 2017, at 11:38 AM, Lu, Yingqi <yingqi.lu at intel.com> wrote:
>
> The webrev.08 is available at
> http://cr.openjdk.java.net/~kkharbas/8164900/webrev.08/
>
> It supposes to address the following the issues. Please let me know if there
> is anything missing.
>
>
> I was off yesterday so I need to catch up here.
>
> On Sep 7, 2017, at 12:52 AM, huaming.li at oracle.com wrote:
>
> I applied the patch, face following compilation error, I worked on Mac,
> Darwin Kernel Version 16.7.0.
>
> /workspace/jdk/jdk10/jdk/src/java.base/unix/classes/sun/nio/fs/UnixChannelFactory.java:247:
> error: cannot find symbol
>             oflags |= O_DIRECT;
>                       ^
>   symbol:   variable O_DIRECT
>   location: class UnixChannelFactory
>
> The same failure occurs of course on Solaris. In the build phase it is
> resolved by
>
> --- a/src/java.base/unix/classes/sun/nio/fs/UnixConstants.java.template
> +++ b/src/java.base/unix/classes/sun/nio/fs/UnixConstants.java.template
> @@ -72,6 +72,9 @@
>
>
>
>  #ifdef O_DIRECT
>      static final int PREFIX_O_DIRECT = O_DIRECT;
> +#else
> +    // not supported (dummy values will not be used at runtime).
> +    static final int PREFIX_O_DIRECT = 00;
>  #endif
>
>
>
>      static final int PREFIX_S_IAMB =
>

Sorry but this is now getting a little confusing as it seems we have
two different mail threads for this topic.

To resolve the build issue we not only need the patch proposed by
Brian, but also the following build patch which I've already sent you
four days before on the other mail thread [1]:

The problem on Linux is caused by the fact that the build doesn't use
"-D_GNU_SOURCE" when processing UnixConstants.java.template and
therefore "O_DIRECT" isn't visible. In contrast, the compilation of
"FileDispatcherImpl.c" always uses "-D_GNU_SOURCE", so you can freely
access "O_DIRECT".

A quick fix is the following:

diff -r 0c49baac8805 make/gensrc/GensrcMisc.gmk
--- a/make/gensrc/GensrcMisc.gmk        Wed Aug 30 18:54:50 2017 +0200
+++ b/make/gensrc/GensrcMisc.gmk        Mon Sep 04 19:37:35 2017 +0200
@@ -63,7 +63,7 @@
 define generate-preproc-src
        $(call MakeDir, $(@D))
        ( $(NAWK) '/@@END_COPYRIGHT@@/{exit}1' $< && \
-         $(CPP) $(CPP_FLAGS) $(SYSROOT_CFLAGS) $< \
+         $(CPP) $(CPP_FLAGS) $(SYSROOT_CFLAGS) $(CFLAGS_JDKLIB) $< \
              2> >($(GREP) -v '^$(<F)$$' >&2) \
              | $(NAWK) '/@@START_HERE@@/,0' \
              |  $(SED) -e 's/@@START_HERE@@/\/\/ AUTOMATICALLY
GENERATED FILE - DO NOT EDIT/' \

which worked for me on Linux/Solaris/AIX (haven't tested on Mac).

I think it was always a mistake that we haven't generated the
UnixConstants with the same C-Flags that we've also used to compile
the files which used them. It was probably just luck that we've not
run into problems until now.

[1] http://mail.openjdk.java.net/pipermail/nio-dev/2017-September/004478.html

> I am currently running a build+regression job on Linux, macOS, Solaris, and
> Windows.
>
> Thanks,
>
> Brian