BUG REPORT: XFS LOG FORWARD COMPATIBILITY PROBLEM

[Eddy Zhao]

Hello Eric:

>
> A tool that can be very helpful here is "pahole" found in the dwarves
> package:
>

Nice tool.

>
> So just to be clear, on 2.6.28, arm eabi logs replay fine on x86_64?
>

I don't have x86_64 machine at hand. Replay arm eabi log on ia32 machine
"seems" success (mount "successfully" returns). Actually I guess that's
because 2.6.28 XFS running on ia32 misinterprets unpacked
xfs_inode_log_format produced by arm as xfs_inode_log_format_64. And there
must be something silently goes wrong on disk after replaying the log.
During fixing the problem, I find it is difficult to change the code to
commit packed log item (restricted by xfs_log_iovec_t mechanism). If we
could somehow change this piece of code to use packed structure. The
endianess problem could be solved by add an byte-swap option to xfs_repair
(like e2fsck "-s"). Then we solve the xfs-log-cant-migrate-between-archs
problem.

Thanks
Eddy
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