Re: [concept & "good taste" review] persistent store

H. Peter Anvin
2010-12-17T23:14:00Z

On 12/17/2010 03:08 PM, Tony Luck wrote:
>
> Do we have any good models for "journals" ... apart from
> the console log? Ying & I did talk about just using printk
> to drop all the saved information onto the console (with
> some sort of "previous" prefix on each line to make
> it easy to find, and to make sure that someone glancing
> at the messages wouldn't worry that that OOPs scrolling
> by was happening now). But this seemed like a really bad
> idea (especially if someone has enough persistent store to
> capture all of __logbuf).
>
> So the downside of "everything is a file" is that we don't
> have much infrastructure for things that don't look like
> files - and trying to build some results in some special
> custom tools being needed to access the data, which
> just makes things harder to use.
>
> People trying to write to /dev/pstore will figure out quickly
> that you can't do that. There are no "ops" to make new files,
> directories, symlinks or even to rename existing ones. You
> can overwrite existing files (because I don't trap "open" to
> deny them write access - but the 0444 mode is supposed
> to be a visual clue to not do that).
>

There are two models I can think of:

1. a file where the head is automatically dropped as space requires.
2. a filesystem where the oldest files are automatically reclaimed.

1 has been implemented in actual systems, 2 is kind of a logical extension.

-hpa