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Date: Wed, 6 Aug 2008 12:29:34 +0100 From: tvrtko.ursulin@...hos.com To: Nick Piggin <nickpiggin@...oo.com.au> Cc: Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org, malware-list@...ts.printk.net Subject: Re: [malware-list] [RFC 0/5] [TALPA] Intro to a linux interface for on access scanning Nick Piggin <nickpiggin@...oo.com.au> wrote on 06/08/2008 12:10:58: > On Wednesday 06 August 2008 19:44, tvrtko.ursulin@...hos.com wrote: > > Nick Piggin wrote on 05/08/2008 19:08:05: > > > On Tuesday 05 August 2008 07:00, Eric Paris wrote: > > > > 5. Define which filesystems are cacheable and which are not > > > > > > This is practically impossible to do completely without rewriting a lot > > > of code (which will never be accepted). I don't see why it is needed > > > > though > > > > > as the filesystem cache is supposed to be kept coherent with disk. > > > > Problem is with network filesystems. So could it be a flag somewhere per > > filesystem which would say something like "this filesystem guarantees > > content of a file cannot change without get_write_access or > > file_update_time being called locally"? That doesn't sound like a lot of > > code so what am I missing? > > Maybe... but that's not the same as what requirement 5 calls for. I see what you mean, it should have been worded better. Nevertheless that is what was intended by it - to enable caching only on filesystems where it is safe to do so. > But depending on exactly what semantics you really call for, it can get > tricky to account for all of pagecache. Writes can happen through page > tables or get_user_pages. True that a process has to at some point have > write permission to the file, but the cache itself could be modified > even after the file is closed and all mmaps disappear. I don't have a very good understanding of the VM subsystem I must admit. So in other words with the current kernel file modification time is not necessarily correct - it represents when the file was last opened for modification, not when it was actually modified? (While those two points in time can be arbitrarily separated) How would I use those methods for file modification? I am curious to make a test case.. Tvrtko Sophos Plc, The Pentagon, Abingdon Science Park, Abingdon, OX14 3YP, United Kingdom. Company Reg No 2096520. VAT Reg No GB 348 3873 20. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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