initramfs: refactor do_header() cpio magic checks

Patch series "initramfs: "crc" cpio format and INITRAMFS_PRESERVE_MTIME", v7.

This patchset does some minor initramfs refactoring and allows cpio entry
mtime preservation to be disabled via a new Kconfig
INITRAMFS_PRESERVE_MTIME option.

Patches 4/6 to 6/6 implement support for creation and extraction of "crc"
cpio archives, which carry file data checksums.  Basic tests for this
functionality can be found at https://github.com/rapido-linux/rapido/pull/163

This patch (of 6):

do_header() is called for each cpio entry and fails if the first six bytes
don't match "newc" magic.  The magic check includes a special case error
message if POSIX.1 ASCII (cpio -H odc) magic is detected.  This special
case POSIX.1 check can be nested under the "newc" mismatch code path to
avoid calling memcmp() twice in a non-error case.

Link: https://lkml.kernel.org/r/20220404093429.27570-1-ddiss@suse.de
Link: https://lkml.kernel.org/r/20220404093429.27570-2-ddiss@suse.de
Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/init/initramfs.c b/init/initramfs.c
index 2f3d96d..2f79b3e 100644 (file)
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -257,12 +257,11 @@ 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);