[PATCH 1/5] initramfs: move unnecessary memcmp from hot path

@@ -256,12 +256,11 @@ static int __init do_collect(void)
 
 static int __init do_header(void)
 {
-	if (memcmp(collected, "070707", 6)==0) {
-		error("incorrect cpio method used: use -H newc option");
-		return 1;
-	}
 	if (memcmp(collected, "070701", 6)) {
-		error("no cpio magic");
+		if (memcmp(collected, "070707", 6) == 0)
+			error("incorrect cpio method used: use -H newc option");
+		else
+			error("no cpio magic");
 		return 1;
 	}
 	parse_header(collected);

@@ -257,7 +257,7 @@ static int __init do_collect(void)
 static int __init do_header(void)
 {
 	if (memcmp(collected, "070701", 6)) {
-		if (memcmp(collected, "070707", 6) == 0)
+		if (memcmp(collected, "0707", 4) == 0)
 			error("incorrect cpio method used: use -H newc option");
 		else
 			error("no cpio magic");

@@ -14,10 +14,10 @@ is different.  The initramfs buffer contains an archive which is
 expanded into a ramfs filesystem; this document details the format of
 the initramfs buffer format.
 
-The initramfs buffer format is based around the "newc" or "crc" CPIO
-formats, and can be created with the cpio(1) utility.  The cpio
-archive can be compressed using gzip(1).  One valid version of an
-initramfs buffer is thus a single .cpio.gz file.
+The initramfs buffer format is based around the "newc" CPIO format, and
+can be created with the cpio(1) utility.  The cpio archive can be
+compressed using gzip(1).  One valid version of an initramfs buffer is
+thus a single .cpio.gz file.
 
 The full format of the initramfs buffer is defined by the following
 grammar, where::

@@ -40,9 +40,8 @@ grammar, where::
 
 
 In human terms, the initramfs buffer contains a collection of
-compressed and/or uncompressed cpio archives (in the "newc" or "crc"
-formats); arbitrary amounts zero bytes (for padding) can be added
-between members.
+compressed and/or uncompressed cpio archives (in the "newc" format),
+with arbitrary amount of zero-byte padding between members.
 
 The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
 not ignored; see "handling of hard links" below.

@@ -55,7 +54,7 @@ by the ASCII string "000012ac"):
 ============= ================== ==============================================
 Field name    Field size	 Meaning
 ============= ================== ==============================================
-c_magic	      6 bytes		 The string "070701" or "070702"
+c_magic	      6 bytes		 The string "070701"
 c_ino	      8 bytes		 File inode number
 c_mode	      8 bytes		 File mode and permissions
 c_uid	      8 bytes		 File uid

@@ -68,8 +67,7 @@ c_min	      8 bytes		 Minor part of file device number
 c_rmaj	      8 bytes		 Major part of device node reference
 c_rmin	      8 bytes		 Minor part of device node reference
 c_namesize    8 bytes		 Length of filename, including final \0
-c_chksum      8 bytes		 Checksum of data field if c_magic is 070702;
-				 otherwise zero
+c_chksum      8 bytes		 Ignored; reserved for unsupported "crc" format
 ============= ================== ==============================================
 
 The c_mode field matches the contents of st_mode returned by stat(2)

@@ -78,12 +76,6 @@ on Linux, and encodes the file type and file permissions.
 The c_filesize should be zero for any file which is not a regular file
 or symlink.
 
-The c_chksum field contains a simple 32-bit unsigned sum of all the
-bytes in the data field.  cpio(1) refers to this as "crc", which is
-clearly incorrect (a cyclic redundancy check is a different and
-significantly stronger integrity check), however, this is the
-algorithm used.
-
 If the filename is "TRAILER!!!" this is actually an end-of-archive
 marker; the c_filesize for an end-of-archive marker must be zero.
 

@@ -378,13 +378,9 @@ static int __init do_name(void)
 static int __init do_copy(void)
 {
 	if (byte_count >= body_len) {
-		struct timespec64 t[2] = { };
 		if (xwrite(wfile, victim, body_len, &wfile_pos) != body_len)
 			error("write error");
-
-		t[0].tv_sec = mtime;
-		t[1].tv_sec = mtime;
-		vfs_utimes(&wfile->f_path, t);
+		do_utime(collected, mtime);
 
 		fput(wfile);
 		eat(body_len);

@@ -1324,6 +1324,16 @@ config BOOT_CONFIG
 
 	  If unsure, say Y.
 
+config INITRAMFS_PRESERVE_MTIME
+	bool "Preserve cpio archive mtimes in initramfs"
+	default y
+	help
+	  Each entry in an initramfs cpio archive carries an mtime value. When
+	  enabled, extracted cpio items take this mtime, with directory mtime
+	  setting deferred until after creation of any child entries.
+
+	  If unsure, say Y.
+
 choice
 	prompt "Compiler optimization level"
 	default CC_OPTIMIZE_FOR_PERFORMANCE

@@ -11,6 +11,9 @@ obj-y                          += noinitramfs.o
 else
 obj-$(CONFIG_BLK_DEV_INITRD)   += initramfs.o
 endif
+ifeq ($(CONFIG_INITRAMFS_PRESERVE_MTIME),y)
+obj-$(CONFIG_BLK_DEV_INITRD)   += initramfs_mtime.o
+endif
 obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
 
 obj-y                          += init_task.o

@@ -16,6 +16,8 @@
 #include <linux/namei.h>
 #include <linux/init_syscalls.h>
 
+#include "initramfs_mtime.h"
+
 static ssize_t __init xwrite(struct file *file, const char *p, size_t count,
 		loff_t *pos)
 {

@@ -115,46 +117,6 @@ static void __init free_hash(void)
 	}
 }
 
-static long __init do_utime(char *filename, time64_t mtime)
-{
-	struct timespec64 t[2];
-
-	t[0].tv_sec = mtime;
-	t[0].tv_nsec = 0;
-	t[1].tv_sec = mtime;
-	t[1].tv_nsec = 0;
-	return init_utimes(filename, t);
-}
-
-static __initdata LIST_HEAD(dir_list);
-struct dir_entry {
-	struct list_head list;
-	char *name;
-	time64_t mtime;
-};
-
-static void __init dir_add(const char *name, time64_t mtime)
-{
-	struct dir_entry *de = kmalloc(sizeof(struct dir_entry), GFP_KERNEL);
-	if (!de)
-		panic_show_mem("can't allocate dir_entry buffer");
-	INIT_LIST_HEAD(&de->list);
-	de->name = kstrdup(name, GFP_KERNEL);
-	de->mtime = mtime;
-	list_add(&de->list, &dir_list);
-}
-
-static void __init dir_utime(void)
-{
-	struct dir_entry *de, *tmp;
-	list_for_each_entry_safe(de, tmp, &dir_list, list) {
-		list_del(&de->list);
-		do_utime(de->name, de->mtime);
-		kfree(de->name);
-		kfree(de);
-	}
-}
-
 static __initdata time64_t mtime;
 
 /* cpio header parsing */

@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/syscalls.h>
+#include <linux/utime.h>
+#include <linux/file.h>
+#include <linux/init_syscalls.h>
+
+#include "initramfs_mtime.h"
+
+long __init do_utime(char *filename, time64_t mtime)
+{
+	struct timespec64 t[2];
+
+	t[0].tv_sec = mtime;
+	t[0].tv_nsec = 0;
+	t[1].tv_sec = mtime;
+	t[1].tv_nsec = 0;
+	return init_utimes(filename, t);
+}
+
+static __initdata LIST_HEAD(dir_list);
+struct dir_entry {
+	struct list_head list;
+	char *name;
+	time64_t mtime;
+};
+
+void __init dir_add(const char *name, time64_t mtime)
+{
+	struct dir_entry *de = kmalloc(sizeof(struct dir_entry), GFP_KERNEL);
+	if (!de)
+		panic("can't allocate dir_entry buffer");
+	INIT_LIST_HEAD(&de->list);
+	de->name = kstrdup(name, GFP_KERNEL);
+	de->mtime = mtime;
+	list_add(&de->list, &dir_list);
+}
+
+void __init dir_utime(void)
+{
+	struct dir_entry *de, *tmp;
+	list_for_each_entry_safe(de, tmp, &dir_list, list) {
+		list_del(&de->list);
+		do_utime(de->name, de->mtime);
+		kfree(de->name);
+		kfree(de);
+	}
+}

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifdef CONFIG_INITRAMFS_PRESERVE_MTIME
+long do_utime(char *filename, time64_t mtime) __init;
+void dir_add(const char *name, time64_t mtime) __init;
+void dir_utime(void) __init;
+#else
+static long __init do_utime(char *filename, time64_t mtime) { return 0; }
+static void __init dir_add(const char *name, time64_t mtime) {}
+static void __init dir_utime(void) {}
+#endif