Re: [9fans] full fossil follies

["adr via 9fans" <9fans@9fans.net>]

On Fri, Jun 25, 2021 at 05:17:39PM +0200, tlaronde@polynum.com wrote:
> On Fri, Jun 25, 2021 at 02:12:07PM +0000, adr via 9fans wrote:
> > On Fri, Jun 25, 2021 at 01:41:30PM +0100, Richard Miller wrote:
> > > > it just becomes difficult
> > > > to do anything when no fossil blocks can be allocated
> > > 
> > > Thinking a bit further about this: intuitively one might expect to be
> > > able to reboot using a local file system which is completely full, and
> > > use du and ls to find big files and rm to delete them, without the need
> > > to allocate new blocks. Something in the way fossil works, makes this
> > > impossible at present. I wonder how much work it would be to investigate
> > > and fix?
> > 
> > I haven't studied how fossil works, so excuse this light chat.
> > Couldn't fossil have reserved blocks so when it starts and it's
> > full it can add those block and present the user to a recovery
> > session? Just a console session printing the last file modified?
> 
> I don't think I will tell anybody a scoop, but it is what is present in
> traditional Unix filesystems where there is a percent of the storage
> preserved... but for root, user under which you are not supposed to
> log to the system in normal operation. This is probably the problem:
> since there is no privileged user, for "whom" to preserve/reserve these
> blocks?

I don't think there is need of superuser concept here. What I'm
imagining, again, without having seen the source code, is something
like this:

The file system is formatted and data representing the structure of
the file system are stored normally.

At execution time, the file server check a flag stored in some
place to see if the system is full. If not, the data is changed so
the blocks are "hidden" and execution continues.

If the system is full, the file system starts a console session
presenting the last file edited. At the end of the session, if the
number of free blocks is bigger than the reserved blocks, the blocks are
"hidden" and execution continues. If not, the console session gives
an error and continues.

The flag can be turn on at the same place the error of file system
full is triggered.

Again, easy talk, I haven't studied the source and a lot of people
have said in this list that fossil is very complex. Some times the
complexity of a task results in a complex implementation. You can't
screw 1000 screws in a minute without a mechanical tool. What I
don't know jet is if the complexity of fossil match its features.
At least I can df all partitions...

adr.

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