Mount on a LE machine a filesystem formatted for BE is not supported currently. This adds a check for the superblock magic number using swapped bytes to guess and warn the user that it may be a valid superblock but endian is incompatible.
MFC after: 2 weeks
The following kernel output is seen when endian mismatch is detected:
Trying to mount root from ufs:/dev/vtbd0s3 []...
UFS2 superblock failed: possible endian mismatch between machine and filesystem
Attempted recovery for standard superblock: failed
Attempted extraction of recovery data from standard superblock: failed
Attempt to find boot zone recovery data.
panic: ffs_use_bread: non-NULL *bufp 0xc00800001b2868b0
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