[LU-13338] add changelog mask per registered user

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Assignee: Mikhail Pershin
• Reporter: Andreas Dilger

Description

Currently, the changelog mask is a global value configured on the MDD device. If changelog users are configured, by default all operation types are logged excluding OPEN, ATIME, and GXATTR (see CHANGELOG_DEFMASK). This adds overhead on the MDT to log a lot of records that may not be interesting for any of the currently-registered users. While it is possible to disable specific record types globally, it is difficult to determine which Changelog users need which record types, and removing records that an administrator thinks are not needed may break the application.

It would be more useful for Changelog users to register the mask of record types that they are interested in, and the union of all registered user masks would determine which records are stored in the changelog. That way, if there is only one changelog user and it is only interested in OPEN and CLOSE records, those would be the only records logged. If a second changelog user is only interested in CREAT and UNLINK then those would also be logged for the duration that changelog user exists, but would stop being logged if the user is deregistered (explicitly or due to lack of record consumption).

This will reduce Changelog overhead in many cases, and avoid potential errors from the configuration of the global flag.

Issue Links

• duplicates: LU-13055 add ability for named Changelog consumers
• is related to: LU-13055 add ability for named Changelog consumers