Project Status Update No. 7

Welcome to the precached project status update No. 7!

In this cycle we mainly concentrated on extending the new rule engine and on fixing bugs throughout the whole project.

What has been achieved

The companion tool iotracectl learned the new paramater --flags that may be used on the subcommands filter, show and remove. This new parameter allows to filter for a specific flag state.

Flags may be one of:

• Valid, meaning that the I/O trace is valid and will be used by the precached prefetcher
• Invalid, meaning that the I/O trace is invalid and will not be used by the precached prefetcher
• Fresh, meaning that the I/O trace is younger than the expiry time
• Expired, meaning that the I/O trace is old and expired, though it maybe still useful (precached will re-trace the associated executable on next execution)
• Current, meaning that the I/O trace is younger than the modification time of the corresponding binary
• Outdated, the binary that has been traced got updated (mtime newer), making the trace irrelevant (precached will re-trace the associated executable on next execution)

Besides that, we extended the rule engine, which is now able to catch the following events:

• Noop: Does nothing at all, just a placeholder
• Ping: Internal Ping event; may be used as a timer or liveness check
• UserLogin: This event gets fired when precached notices that a user has logged in on the system

New and noteworthy actions are:

• Noop: Does nothing at all, just a placeholder
• Log: Log a message to syslog, the text can be given in the Message: argument
• Notify: Send a desktop notification to the first logged in user
• CacheDirRecursive: Recursively statx() files in the directory given in Directory: argument

In addition the rule engine learned to expand variables and macros in all strings given to it.

E.g. the following rule stanza

# Event-Name		  Filter		  Action		  Arguments
UserLogin		  Noop              Log                 Severity:Warn,Message:"$date User $user logged in! ($home_dir)"
UserLogin               Noop              CacheDirRecursive   Directory:"$home_dir/.gnome"

will be processed and finally be expanded to this equivalent:

# Event-Name		  Filter		  Action		  Arguments
UserLogin		  Noop              Log                 Severity:Warn,Message:"2018-01-14 08:59 User admin logged in! (/home/admin)"
UserLogin               Noop              CacheDirRecursive   Directory:"/home/admin/.gnome"

List of new and noteworthy plugins

• Janitor: A janitor for precached that handles all house keeping tasks
• Rule Engine: Learned a few new features like variable and macro expansion (see above)
• Rule Event Bridge: Serves as a gateway between precached internals and the rule engine
• User Session: The caching related code, mainly the caching-of-directories-on-user-login feature has been superseded by a .rule file

The precached team