File perforation.

[David Woodhouse <dwmw2@infradead.org>]

I keep receiving requests from users to allow space saving by making holes 
in files. For people using JFFS2, a compressed file system designed for use 
on fairly small solid state storage devices, this is a fairly reasonable 
request, and it's also fairly simple to implement. It's only the interface 
I'm concerned about.

I've been resisting these requests because I really don't want to do it 
with an ioctl on the file. Only if we can have a generic sys_perforate() 
would I really want to do it.

Apparently it's hard to implement on block-based file systems. I don't 
really care about that though -- just falling back to writing zeroes to the 
offending range (or indeed returning -EINVAL) would be perfectly sufficient 
until/unless it gets implemented for other file systems. All I want is an 
interface that doesn't make me feel dirty :)

Comments? 

--
dwmw2