Hi all, MMP feature of ext4 really helps us a lot to avoid mounting file system more than once, especailly when using ext4 as the basis of a distributed file sytem, e.g. Lustre. However, lack of a userspace utility to check the status of MMP makes it diffcult to utilize this feature to make failover decisions. We tried to write a script to do so by parsing the output of debugfs command. But this solution is not very straight forward. In order to check the sequence and checksum correctly, the script has to embed a lot of value definition, which could be error prone. Finally, we decided to add a new command in the e2fsprogs. With that command, a server is able to check the current MMP state of a device so that it can decide whether to take over the file system service from aother server. I think the patch might helps other use cases too. The attachment is the patch. Thanks, Li Xi
Attachment:
mmpstatus.patch
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