gnu: strace: Fix build failure on Linux-Libre 4.16.

* gnu/packages/patches/strace-kernel-4.16.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/linux.scm (strace)][source](patches): New field.

gnu/local.mk

@@ -1096,6 +1096,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/slim-login.patch				\
   %D%/packages/patches/sooperlooper-build-with-wx-30.patch 	\
   %D%/packages/patches/steghide-fixes.patch			\
+  %D%/packages/patches/strace-kernel-4.16.patch			\
   %D%/packages/patches/superlu-dist-scotchmetis.patch		\
   %D%/packages/patches/swish-e-search.patch			\
   %D%/packages/patches/swish-e-format-security.patch		\

gnu/packages/linux.scm

@@ -949,6 +949,7 @@ Zerofree requires the file system to be unmounted or mounted read-only.")
              (method url-fetch)
              (uri (string-append home-page "/files/" version
                                  "/strace-" version ".tar.xz"))
+             (patches (search-patches "strace-kernel-4.16.patch"))
              (sha256
               (base32
                "17dkpnsjxmys1ydidm9wcvc3wscsz44fmlxw3dclspn9cj9d1306"))))

gnu/packages/patches/strace-kernel-4.16.patch

@@ -0,0 +1,92 @@
+Fix test failure when using Linux-Libre >= 4.16.
+
+Taken from upstream:
+https://github.com/strace/strace/commit/bcff87c31c0f27c678a43d6b7f67dab363a974fa
+
+From bcff87c31c0f27c678a43d6b7f67dab363a974fa Mon Sep 17 00:00:00 2001
+From: Masatake YAMATO <yamato@redhat.com>
+Date: Wed, 2 May 2018 17:11:07 +0900
+Subject: [PATCH] tests/ioctl_kvm_run.c: handle cpuid at the end of vcpu dentry
+
+Since Linux 4.16, kernel appends the cpuid as suffix to the entry
+for a kvm vcpu in /proc/$pid/fd like:
+
+    anon_inode:kvm-vcpu:0
+
+That was
+
+    anon_inode:kvm-vcpu
+
+This kernel change causes the test case failure on newer kernels.
+Update the test to deal with the new name as well as the old one.
+
+* tests/ioctl_kvm_run.c: Include unistd.h for using readlink(2).
+(vcpu_dev_should_have_cpuid): New function for detecting whether
+a proc entry for given fd has the cpuid suffix or not.
+(main): Trim vcpu_dev to remove the cpuid suffix if needed.
+(vcpu_dev): Remove const modifier.
+---
+ tests/ioctl_kvm_run.c | 29 ++++++++++++++++++++++++++++-
+ 1 file changed, 28 insertions(+), 1 deletion(-)
+
+diff --git a/tests/ioctl_kvm_run.c b/tests/ioctl_kvm_run.c
+index 179461430..e1bef5796 100644
+--- a/tests/ioctl_kvm_run.c
++++ b/tests/ioctl_kvm_run.c
+@@ -40,6 +40,7 @@
+ # include <string.h>
+ # include <sys/ioctl.h>
+ # include <sys/mman.h>
++# include <unistd.h>
+ # include <linux/kvm.h>
+ 
+ static int
+@@ -56,7 +57,7 @@ kvm_ioctl(int fd, unsigned long cmd, const char *cmd_str, void *arg)
+ 
+ static const char dev[] = "/dev/kvm";
+ static const char vm_dev[] = "anon_inode:kvm-vm";
+-static const char vcpu_dev[] = "anon_inode:kvm-vcpu";
++static char vcpu_dev[] = "anon_inode:kvm-vcpu:0";
+ static size_t page_size;
+ 
+ extern const char code[];
+@@ -165,6 +166,23 @@ run_kvm(const int vcpu_fd, struct kvm_run *const run, const size_t mmap_size,
+ 	}
+ }
+ 
++static int
++vcpu_dev_should_have_cpuid(int fd)
++{
++	int r = 0;
++	char *filename = NULL;
++	char buf[sizeof(vcpu_dev)];
++
++	if (asprintf(&filename, "/proc/%d/fd/%d", getpid(), fd) < 0)
++		error_msg_and_fail("asprintf");
++
++	if (readlink(filename, buf, sizeof(buf)) == sizeof(buf) - 1
++	    && (memcmp(buf, vcpu_dev, sizeof(buf) - 1) == 0))
++		r = 1;
++	free(filename);
++	return r;
++}
++
+ int
+ main(void)
+ {
+@@ -208,6 +226,15 @@ main(void)
+ 	       (unsigned long) page_size, (unsigned long) page_size, mem);
+ 
+ 	int vcpu_fd = KVM_IOCTL(vm_fd, KVM_CREATE_VCPU, NULL);
++	if (!vcpu_dev_should_have_cpuid(vcpu_fd))
++		/*
++		 * This is an older kernel that doesn't place a cpuid
++		 * at the end of the dentry associated with vcpu_fd.
++		 * Trim the cpuid part of vcpu_dev like:
++		 * "anon_inode:kvm-vcpu:0" -> "anon_inode:kvm-vcpu"
++		 */
++		vcpu_dev[strlen (vcpu_dev) - 2] = '\0';
++
+ 	printf("ioctl(%d<%s>, KVM_CREATE_VCPU, 0) = %d<%s>\n",
+ 	       vm_fd, vm_dev, vcpu_fd, vcpu_dev);
+