gnu: python@2.7: Fix getentropy() calls on kernels < 3.17.

* gnu/packages/patches/python-2.7-getentropy-on-old-kernels.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/python.scm (python-2.7)[source]: Use it.

gnu/local.mk

@@ -848,6 +848,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/pygpgme-disable-problematic-tests.patch  \
   %D%/packages/patches/pyqt-configure.patch			\
   %D%/packages/patches/python-2-deterministic-build-info.patch	\
+  %D%/packages/patches/python-2.7-getentropy-on-old-kernels.patch	\
   %D%/packages/patches/python-2.7-search-paths.patch		\
   %D%/packages/patches/python-2.7-site-prefixes.patch		\
   %D%/packages/patches/python-2.7-source-date-epoch.patch	\

gnu/packages/patches/python-2.7-getentropy-on-old-kernels.patch

@@ -0,0 +1,54 @@
+This patch resolves a compatibility issue when compiled against glibc
+2.25
+and run runder kernels < 3.17:
+
+https://bugzilla.redhat.com/show_bug.cgi?id=1410175
+
+Upstream bug URLs:
+
+https://bugs.python.org/issue29157
+https://bugs.python.org/issue29188
+
+Patch adapted from upstream source repository:
+
+https://github.com/python/cpython/commit/01bdbad3e951014c58581635b94b22868537901c
+
+From 01bdbad3e951014c58581635b94b22868537901c Mon Sep 17 00:00:00 2001
+From: Victor Stinner <victor.stinner@gmail.com>
+Date: Mon, 9 Jan 2017 11:10:41 +0100
+Subject: [PATCH] Don't use getentropy() on Linux
+
+Issue #29188: Support glibc 2.24 on Linux: don't use getentropy() function but
+read from /dev/urandom to get random bytes, for example in os.urandom().  On
+Linux, getentropy() is implemented which getrandom() is blocking mode, whereas
+os.urandom() should not block.
+---
+ Misc/NEWS       |  5 +++++
+ Python/random.c | 11 +++++++++--
+ 2 files changed, 14 insertions(+), 2 deletions(-)
+
+diff --git a/Python/random.c b/Python/random.c
+index 57c41ffcd6..000cb36938 100644
+--- a/Python/random.c
++++ b/Python/random.c
+@@ -97,8 +97,15 @@ win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
+ }
+ 
+ /* Issue #25003: Don't use getentropy() on Solaris (available since
+- * Solaris 11.3), it is blocking whereas os.urandom() should not block. */
+-#elif defined(HAVE_GETENTROPY) && !defined(sun)
++   Solaris 11.3), it is blocking whereas os.urandom() should not block.
++
++   Issue #29188: Don't use getentropy() on Linux since the glibc 2.24
++   implements it with the getrandom() syscall which can fail with ENOSYS,
++   and this error is not supported in py_getentropy() and getrandom() is called
++   with flags=0 which blocks until system urandom is initialized, which is not
++   the desired behaviour to seed the Python hash secret nor for os.urandom():
++   see the PEP 524 which was only implemented in Python 3.6. */
++#elif defined(HAVE_GETENTROPY) && !defined(sun) && !defined(linux)
+ #define PY_GETENTROPY 1
+ 
+ /* Fill buffer with size pseudo-random bytes generated by getentropy().
+-- 
+2.12.0
+

gnu/packages/python.scm

@@ -133,7 +133,8 @@
       (patches (search-patches "python-2.7-search-paths.patch"
                                "python-2-deterministic-build-info.patch"
                                "python-2.7-site-prefixes.patch"
-                               "python-2.7-source-date-epoch.patch"))
+                               "python-2.7-source-date-epoch.patch"
+                               "python-2.7-getentropy-on-old-kernels.patch"))
       (modules '((guix build utils)))
       ;; suboptimal to delete failing tests here, but if we delete them in the
       ;; arguments then we need to make sure to strip out that phase when it