bin/45072: fsck_ext2fs dosn't work well with ext2fs's without alternate superblocks

[jasper%pointless.net@localhost]

>Number:         45072
>Category:       bin
>Synopsis:       fsck_ext2fs dosn't work well with ext2fs's without alternate 
>superblocks
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 17 04:15:00 +0000 2011
>Originator:     Jasper Wallace
>Release:        5.99.48
>Organization:
Pointless.net
>Environment:
NetBSD limpit 5.99.48 NetBSD 5.99.48 (GENERIC) #0: Fri Jun 10 20:46:16 BST 2011 
 
jasper@limpit:/home/jasper/develop/netbsd/netbsd-src-and-build/tree/n.64/obj/sys/arch/amd64/compile/GENERIC
 amd64
>Description:
I dual boot my laptop between ubuntu and netbsd with my /home on ext2. At some 
point an ubunut upgrade changed /home to have alternate superblocks that are 
all zero's.

netbsd fsck_ext2fs dosn't like that, and core dumps when attempting to 
construct an alternate superblock cos i don't have fsize set in the disklabel 
(which i should probably have, but on the other hand fsck should cope 
gracefuly).

>How-To-Repeat:
run netbsd fsck_ext2fs against my /home.

N.B. i'm not sure of the sequence of events that produced this file system, i 
don't know if a modern mke2fs would do the same thing.

It may of been made with the sparse_super option, however fsck.ext2 (the linux 
version) dosn't find an alternate superblocks either.

>Fix:
Index: setup.c
===================================================================
RCS file: /cvsroot/src/sbin/fsck_ext2fs/setup.c,v
retrieving revision 1.27
diff -u -r1.27 setup.c
--- setup.c     19 Oct 2009 18:41:08 -0000      1.27
+++ setup.c     17 Jun 2011 03:52:48 -0000
@@ -352,6 +352,17 @@
                return 1;
        }
 
+       if (asblk.b_un.b_fs->e2fs_magic != E2FS_MAGIC) {
+           /* the alternate super-block dosn't have the e2fs magic,
+            * so ignore it.
+            *
+            * XXX e2fsck checks all the superblocks in the system
+            * rather than giving up on the first one
+            *
+            */
+            return 1;
+       }
+
        /*
         * Set all possible fields that could differ, then do check
         * of whole super block against an alternate super block.
@@ -490,6 +501,10 @@
                    fstypenames[pp->p_fstype] : "unknown");
                return 0;
        }
+       if (pp->p_fsize == 0) {
+           pfatal("%s: no fsize set in disklabel.\n", dev);
+           return 0;
+       }
        memset(fs, 0, sizeof(struct m_ext2fs));
        fs->e2fs_bsize = pp->p_fsize;
        fs->e2fs.e2fs_log_bsize = pp->p_fsize / 1024;