Re: [9fans] truncation via wstat on ken's fs

[Russ Cox <russcox@gmail.com>]

> Changing the length is easy, but giving back the no-longer-needed
> blocks is messy, involving a recursive walk of the indirect blocks.
> I'm tempted to just change the length, which gives the desired
> user-visible effect, unless the side-effect of freeing the
> unneeded storage is important to someone.

I thought about this too, but it's not actually true.

It's important to free or zero the blocks:

fd = create("foo", ORDWR);
write(fd, "hello world", 12);
ftruncate(fd, 0);
pwrite(fd, "", 1, 11);

should result in a file with 12 zero bytes,
not the string "hello world\0".

It's not that hard to do the recursive walk.
Remove does it already.  In fossil we just pulled
that code out of remove and made it a separate
function that can be passed a length instead
of assuming 0.

Russ