Sidebar to smbmount patch (re mutating structs)

[David Collier-Brown]

Urban Widmark wrote:
> One of the problems I would like to fix is the dependency between the
> kernel sources (includes) and smbmount. 
[description snipped]

	At the binary level, it's fairly straightforward to 
	deal with callers passing in both "old" and "new"
	formats of struct: just labourious.


> If smbmount is not changed and compiled vs new sources the problem is that
> smbmount sends a version 7 struct with only the version 6 fields
> initialized (it would be fine if it set the version to 6, but it grabs the
> kernel define which now says 7 ...). smbfs can't know this and will fail.

	[anyone interested send me email: I have a paper
	from my Multics days on the subject I can scan or
	type in]

	However, at the source level, there is a question as to
	whether you really want to do so. I assume you wish
	to be able to support smbmount in version x.y and x.y+1
	of Linux (or Solaris, or whatever), and at some later
	date phase out obsolescent versions.

	However, this is "breaking the contract" between the
	producer and the consumer of the struct, and is one of 
	the things one tries not to do.  After banging their
	heads against this for a while, the affected multicians
	seem to have come to a consensus that 
	     1. evolution WILL happen (which is trivially true)
	     2. if you don't evolve, you have to use the sources
		for the old version, and forego the benefits of
		the new version. 
	The result of this is a slow, steady migration forward,
	and a limit on the need for the developers to bugfix
	old versions in parallell with new versions,

	Bugfixing old version while developing new ones is something
	that developers generally get told to do by pointy-haired 
	managers, and cordially hate (;-))

	So I reccomend that smbmount version x.y+1 be #ifdef'd
	so as to require version 7 structs, and produce a
	message explaining this requirement.  In Slolaris cpp,
	this would be:

	#if version != 7
	#error "This programs requires a version 7 fs_t struct \
	 which is available in Linux x.y and later.  For Linux \
	 x.y-1 or earlier, use version m.n of this program."
	#endif

	

--dave
-- 
David Collier-Brown,  | Always do right. This will gratify some people
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