large ufs2 partitions and 'df'

[Kirk McKusick]

	Date: Mon, 12 May 2003 07:53:49 -0700
	From: Terry Lambert <tlambert2 at mindspring.com>
	To: Kirk McKusick <mckusick at mckusick.com>
	CC: Julian Elischer <julian at elischer.org>, freebsd-current at freebsd.org
	Subject: Re: large ufs2 partitions and 'df'
	X-ASK-Info: Whitelist match

	Kirk McKusick wrote:
	> Julian Elisher wrote:
	> > I think that swithing to a new syscall with a fixed structure
	> > and using the rules you mention above to populate the structure in
	> > an ostatfs call might be the best answer.
	> > Old binaries probably only need to know that there is > X blocks
	> > free and not necessarily the correct number.
	> > New binaries can use the new syscall.
	> 
	> So right you are. It would be possible to get the space by nibbling
	> a bit more space from MNAMELEN, but at some point we need to just bite
	> the bullet and define a new structure. I am leaning towards believing
	> that time is now. If we do define a new structure, I would like to
	> clean up the existing one a bit. I would propose this:

	If you're going to change the structure, please put a version
	number as the first field, so that it's never a problem again.

	Also, put a spare field on the end (64 bits) to allow for
	future expansion that maintains binary compatability (by way
	of choice about what to copy in).

	-- Terry

There are already ten spare 64-bit numbers in the middle of the 
proposed new structure. They are there where they are guaranteed
to be 64-bit aligned rather than at the end where there is danger
of them being aligned differently on different architectures since
they follow character arrays.

	Kirk McKusick