f2fs: Add support for reporting a fake kernel version to fsck

fsck.f2fs forces a filesystem fix on boot if it detects that the current
kernel version differs from the one saved in the superblock, which results in
fsck blocking boot for a long time (~35 seconds). This commit provides a
way to report a constant fake kernel version to fsck to avoid triggering
the version check, which is useful if you boot new kernel builds
frequently.

Signed-off-by: Danny Lin <danny@kdrag0n.dev>
Change-Id: I65974f63d81171947399ff31b22fb9e95d14a6f3

Signed-off-by: Carlos Jimenez (JavaShin-X) <javashin1986@gmail.com>

ocean stock-kernel =

CONFIG_F2FS_REPORT_FAKE_KERNEL_VERSION=y
CONFIG_F2FS_FAKE_KERNEL_RELEASE="4.9.206-perf+"
CONFIG_F2FS_FAKE_KERNEL_VERSION="#1 SMP PREEMPT Wed Sep 30 23:50:55 CDT 2020 aarch64"

Signed-off-by: Carlos Jimenez (JavaShin-X) <javashin1986@gmail.com>
Signed-off-by: TogoFire <italomellopereira@gmail.com>

fs/f2fs/Kconfig

@@ -103,3 +103,23 @@ config F2FS_FAULT_INJECTION
 	  Test F2FS to inject faults such as ENOMEM, ENOSPC, and so on.
 
 	  If unsure, say N.
+
+config F2FS_REPORT_FAKE_KERNEL_VERSION
+	bool "Report fake kernel version to fsck.f2fs"
+	depends on F2FS_FS
+	help
+	  fsck.f2fs forces a filesystem fix on boot if it detects that the current
+	  kernel version differs from the one saved in the superblock, which results in
+	  fsck taking a long time to run. This option provides a way to report a
+	  constant fake kernel version to fsck to avoid triggering the version check.
+
+	  If unsure, say N.
+
+config F2FS_FAKE_KERNEL_RELEASE
+	string "Kernel release for fsck.f2fs"
+	depends on F2FS_REPORT_FAKE_KERNEL_VERSION
+
+config F2FS_FAKE_KERNEL_VERSION
+	string "Kernel version for fsck.f2fs"
+	depends on F2FS_REPORT_FAKE_KERNEL_VERSION
+

kernel/sys.c

@@ -1143,6 +1143,28 @@ static int override_release(char __user *release, size_t len)
 	return ret;
 }
 
+static int override_version(struct new_utsname __user *name)
+{
+#ifdef CONFIG_F2FS_REPORT_FAKE_KERNEL_VERSION
+	int ret;
+
+	if (strcmp(current->comm, "fsck.f2fs"))
+		return 0;
+
+	ret = copy_to_user(name->release, CONFIG_F2FS_FAKE_KERNEL_RELEASE,
+			   strlen(CONFIG_F2FS_FAKE_KERNEL_RELEASE) + 1);
+	if (ret)
+		return ret;
+
+	ret = copy_to_user(name->version, CONFIG_F2FS_FAKE_KERNEL_VERSION,
+			   strlen(CONFIG_F2FS_FAKE_KERNEL_VERSION) + 1);
+
+	return ret;
+#else
+	return 0;
+#endif
+}
+
 SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name)
 {
 	struct new_utsname tmp;