Backend 'quiet' print output about ebbrt HOT 6 CLOSED

Here is my thoughts for how to do this. There should be a bunch of logging functions representing various levels of output (trace, debug, warn, info, error). And each of these functions should output based on the current log level (set by default to warn perhaps, but overridable by command line or FDT or environment variable.) This way we don't have to struggle too much for when to put debug output in the code, just choose the appropriate level

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We went through several designs on this topic. Questions about how to keep the checks flexible and
yet potentially eliminate them all together to avoid overheads. (eg. no memory or coherency traffic).

I am happy to chat about the approaches we have looked at in the past.

On Feb 25, 2016, at 11:15 AM, Dan Schatzberg [email protected] wrote:

Here is my thoughts for how to do this. There should be a bunch of logging functions representing various levels of output (trace, debug, warn, info, error). And each of these functions should output based on the current log level (set by default to warn perhaps, but overridable by command line or FDT or environment variable.) This way we don't have to struggle too much for when to put debug output in the code, just choose the appropriate level

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@jappavoo
If possible, add thoughts to this post so we have it all documented.

Another feature I would desire is the ability to enable/disable output per file, perhaps having the functions pass the value of the predefined FILE macro.

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logging functions representing various levels of output (trace, debug, warn, info, error)

Yes, I agree. We'd probably want both a "LogManager" Ebb, or a set of low-level kprintf-like functions (kprinf-debug(), kprintf-error(), kprintf-all()).

ability to enable/disable output per file, perhaps having the functions pass the value of the predefined FILE macro

I'm not sure I follow...a file-specific macro? E.g., __EBBRT_EVENTMANAGER__QUIET_ALL__ ?

We went through several designs on this topic.

Here's a glance into one way we had previously hacked together a 'quiet' build:
546c1f9

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@jmcadden

I'm not sure I follow...a file-specific macro? E.g., EBBRT_EVENTMANAGER__QUIET_ALL ?

I'm motivated by the way Rust's env_logger works: https://rust-lang-nursery.github.io/log/env_logger/

GCC defines __FILE__ to be the current file name. So if we had the (for example) LOG() macro pass the file name to the logging object. Then the logging object could decide to log (or not) based on some file-specific setting. For example, suppose we could configure the log output with some variable like so: EBBRT_LOG="warn,EventManager=debug" then all log output with warn or higher (e.g. error) will be output. However, any output in the EventManager with debug or higher will be output.

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For the time being: EbbRT baremetal has a compilation flag that will mute kprintf() output, along with a force_kprintf() that will print when others are muted.

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