Re: [9fans] bind -c[ab] -- what am I doing wrong?

[andrey mirtchovski <mirtchov@cpsc.ucalgary.ca>]

On Thu, 17 Jul 2003, northern snowfall wrote:

>
> Hope that helps!
>

well, it doesn't. what you describe is the bahaviour of the command
according to the  man page. but here's what I observe:

	plan9% touch kern/test			# clearly I can write to it
	plan9% rm kern/test
	plan9% bind -ac /sys kern
	plan9% touch kern/test			# but not anymore
	touch: kern/test: cannot create: permission denied
	plan9%
	plan9% unmount kern
	plan9% bind -ac kern /sys
	plan9% touch /sys/blah			# this works as expected
	plan9%

given the man page i expect 'bind -ac new /something/i/can/write/to' to
allow me to continue to write to '/something/i/can/write/to'.

in fact, I expect to be able to write to '/something/i/can/write/to'
irregardless of whether it corresponds to 'new', 'old', is bound before or
bound after a directory. the only case when I wouldn't expect to be able to
write to it is when I'm not able to walk to it because of a bind -b earlier
in the walk.

in functional languages this technique is used as a formal proof of
a program's correctness, observe this example from the haskell prelude:

    -- Minimal complete definition: (==) or (/=)
    x == y      = not (x/=y)
    x /= y      = not (x==y)

a similar definition for 'bind' would be:

    bind -cb new old == bind -ca old new

where, of course, we consider only the resulting directory, and not the path
to it.

andrey