Find which files are affected by bad blocks on ext4 filesystem

Question

I have an ext4 filesystem that recently developed some bad sectors. Running fsck.ext4 -c finds and remembers the bad blocks. How can I find which files (if any) included these bad blocks so I can restore them from backups?

Answer 1

With a combination of dumpe2fs and debugfs, which are included in the e2fsprogs package along fsck.ext*.
You must use the output of a command as the argument of the next one.
These tools auto-detect the filesystem block size, so it is consistent and safer than direct badblocks invocation.

Prints the registered bad blocks of the filesystem:

# dumpe2fs -b DEVNAME

Prints the inodes which use the given block list:

# debugfs -R "icheck BLOCK ..." DEVNAME

Prints the pathnames to the given inode list:

# debugfs -R "ncheck INODE ..." DEVNAME

debugfs has also an interactive shell and the -f cmd_file option, but they are not much powerful or useful for this case.
The -R option allows more automated scripts like this:

#!/bin/sh
# Finds files affected by bad blocks on ext* filesystems.
# Valid only for ext* filesystems with bad blocks registered with
# fsck -c [-c] [-k] or -l|-L options.
# Can be extremely slow on damaged storage (not just a corrupt filesystem).

DEVNAME="$1"
[ -b "$DEVNAME" ] || exit 1

BADBLOCKS="$(dumpe2fs -b "$DEVNAME" | tr '\n' ' ')"
[ -n "$BADBLOCKS" ] || exit 0

INODES="$(debugfs -R "icheck $BADBLOCKS" "$DEVNAME" | awk -F'\t' '
    NR > 1 { bad_inodes[$2]++; }
    END {
        for (inode in bad_inodes) {
            if (inode == "<block not found>") {
                printf("%d unallocated bad blocks\n", bad_inodes[inode]) > "/dev/stderr";
                continue;
            }
            printf inode OFS;
        }
    }
')"
[ -n "$INODES" ] || exit 0

debugfs -R "ncheck -c $INODES" "$DEVNAME"