libbpf: Correctly set the kernel code version in Debian kernel.

In a previous commit, Ubuntu kernel code version is correctly set
by retrieving the information from /proc/version_signature.

commit<5b3d72987701d51bf31823b39db49d10970f5c2d>
(libbpf: Improve LINUX_VERSION_CODE detection)

The /proc/version_signature file doesn't present in at least the
older versions of Debian distributions (eg, Debian 9, 10). The Debian
kernel has a similar issue where the release information from uname()
syscall doesn't give the kernel code version that matches what the
kernel actually expects. Below is an example content from Debian 10.

release: 4.19.0-23-amd64
version: #1 SMP Debian 4.19.269-1 (2022-12-20) x86_64

Debian reports incorrect kernel version in utsname::release returned
by uname() syscall, which in older kernels (Debian 9, 10) leads to
kprobe BPF programs failing to load due to the version check mismatch.

Fortunately, the correct kernel code version presents in the
utsname::version returned by uname() syscall in Debian kernels. This
change adds another get kernel version function to handle Debian in
addition to the previously added get kernel version function to handle
Ubuntu. Some minor refactoring work is also done to make the code more
readable.

Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230203234842.2933903-1-hao.xiang@bytedance.com

1 files changed, 0 insertions, 37 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index eed5cec6f510..4191a78b2815 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -34,7 +34,6 @@
 #include <linux/limits.h>
 #include <linux/perf_event.h>
 #include <linux/ring_buffer.h>
-#include <linux/version.h>
 #include <sys/epoll.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
@@ -870,42 +869,6 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 	return 0;
 }
 
-__u32 get_kernel_version(void)
-{
-	/* On Ubuntu LINUX_VERSION_CODE doesn't correspond to info.release,
-	 * but Ubuntu provides /proc/version_signature file, as described at
-	 * https://ubuntu.com/kernel, with an example contents below, which we
-	 * can use to get a proper LINUX_VERSION_CODE.
-	 *
-	 *   Ubuntu 5.4.0-12.15-generic 5.4.8
-	 *
-	 * In the above, 5.4.8 is what kernel is actually expecting, while
-	 * uname() call will return 5.4.0 in info.release.
-	 */
-	const char *ubuntu_kver_file = "/proc/version_signature";
-	__u32 major, minor, patch;
-	struct utsname info;
-
-	if (faccessat(AT_FDCWD, ubuntu_kver_file, R_OK, AT_EACCESS) == 0) {
-		FILE *f;
-
-		f = fopen(ubuntu_kver_file, "r");
-		if (f) {
-			if (fscanf(f, "%*s %*s %d.%d.%d\n", &major, &minor, &patch) == 3) {
-				fclose(f);
-				return KERNEL_VERSION(major, minor, patch);
-			}
-			fclose(f);
-		}
-		/* something went wrong, fall back to uname() approach */
-	}
-
-	uname(&info);
-	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
-		return 0;
-	return KERNEL_VERSION(major, minor, patch);
-}
-
 static const struct btf_member *
 find_member_by_offset(const struct btf_type *t, __u32 bit_offset)
 {