[PATCH, libstdc++]: Fix PR 70975, experimental/filesystem/operations/copy.cc FAILs on Solaris 12

[Jonathan Wakely]

On 27/10/16 20:33 +0200, Uros Bizjak wrote:
>Attached patch improves sendfile syscall compatibility with (older)
>Solaris 12, where non-null third argument is required. It also paves
>the way for compatibility with Solaris 10/11, where otherwise
>additional -lsendfile is needed to link with libsendfile library. The
>change has no effect on linux.
>
>
>2016-10-27  Uros Bizjak  <ubizjak@gmail.com>
>
>    PR libstdc++/70975
>    * src/filesystem/ops.cc (do_copy_file) [_GLIBCXX_USE_SENDFILE]:
>    Use pointer to zero as non-null third argument of sendfile call.
>
>Bootstrapped and regression tested on x86_64-linux-gnu {,-m32} CentOS
>5 and Fedora 24. Also tested by Rainer on older Solaris 12, where the
>patch fixes testsuite failure.
>
>OK for mainline?
>
>Uros.

>diff --git a/libstdc++-v3/src/filesystem/ops.cc b/libstdc++-v3/src/filesystem/ops.cc
>index 9abcee0..b709858 100644
>--- a/libstdc++-v3/src/filesystem/ops.cc
>+++ b/libstdc++-v3/src/filesystem/ops.cc
>@@ -444,7 +444,9 @@ namespace
>       }
>
> #ifdef _GLIBCXX_USE_SENDFILE
>-    const auto n = ::sendfile(out.fd, in.fd, nullptr, from_st->st_size);
>+    off_t always_zero_offset = 0;
>+    const auto n = ::sendfile(out.fd, in.fd,
>+			      &always_zero_offset, from_st->st_size);
>     if (n < 0 && (errno == ENOSYS || errno == EINVAL))
>       {
> #endif

Is there a good reason to call it "always_zero_offset" rather than
something that fits on one line, like "offset"?

OK for trunk anyway, thanks.