Re: Syscall table AKA hijacking syscalls

[Libor Vanek]

> > I'm writing some project which needs to hijack some syscalls in VFS 
> > layer. AFAIK in 2.6 is this "not-wanted" solution (even that there are 
> > some very nasty ways of doing it - see 
> > http://mail.nl.linux.org/kernelnewbies/2002-12/msg00266.html )
> >    
>
> Why do you need to hijack system calls from a module? 99% of the
> times, it's the wrong technical solution. 
>  
I'm working on my diploma thesis which is adding snapshot capability 
into Linux VFS (so you can do directory based snapshots - not complete 
device, like in LVM). It'll consist of two separete modules:
Snapshot module:
- will hijack (one or another way) calls to open/move/unlink/mkdir/etc. 
syscall
- when will detect change to selected directory (which I want to 
snapshot), it'll copy/move old file/directory to some temporary 
(selected when creating snapshot) - in fact - copy on write behaviour

UnionFS module:
- will place "temporary" directory with saved files/dirs "over" actual 
one and result will be read-only snapshot - this can be done without 
hijacking syscalls probably
- something like overlay fs but a bit different

--

Libor Vanek



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