Message-ID: <3FF59073.3060305@conet.cz>
Date: Fri, 02 Jan 2004 16:38:27 +0100
From: Libor Vanek <libor@conet.cz>
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To: Muli Ben-Yehuda <mulix@mulix.org>
CC: linux-kernel@vger.kernel.org
Subject: Re: Syscall table AKA hijacking syscalls
References: <3FF56B1C.1040308@conet.cz> <20040102151206.GJ1718@actcom.co.il>
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>>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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