Subject: Re: ext2fs is in the tree
To: Paul Kranenburg <>
From: Chris G. Demetriou <>
List: current-users
Date: 06/16/1997 10:00:41
> > According to a recent PR, with a fix to vfs_bio.c, LFS at least gets
> > to the point where you can copy a source tree to it, etc.
> > 
> > Of course, Charles vehemently pointed out that that fix was
> > unnecessary and incorrect, when I asked him to look at the PR.
> > (Before one of his mods to the bio code, it had code that did the same
> > thing that the fix does...)
> I looked at the patch briefly last week and thought it didn't handle
> the read-ahead case correctly.

It might not; I didn't look at it that closely, since i've not touched
the buffer cache in a while, since I don't want to go back in there,
and since Charles made the change that appears to have broken it.  8-)

However, he was objecting to the (old) semantics used for the flags,
rather than the actual implementation.

> Today I found myself puzzling once again over relationship between
> several B_* flags. Clearly, not all individual flags can be used
> independently of each other, but it seems that evidence on
> "correct" B_* flag usage can be had only by browsing through 
> pieces of filesystem code.

That is correct, unfortunately.

> A buf(9) is much wanted...

Having a buf(9) would be nice, but wouldn't be able to dictate the
actual ("traditional") behaviour.  It'd have to document it as well as
possible.  Unfortunately, the LFS thing fell outside of the normal,
expected usage of the flags, even though obviously the berkeley buffer
cache (as of 4.4) supported it.

Unfortunately, there's no complete documentation of the buffer cache,
even in Bach or the daemon books.