From: Yiannis Marangos <yiannis.marangos@gmail.com>
Date: Thu, 10 Apr 2014 11:57:43 GMT
Subject: Re: [PATCH v5] Verify index file before we opportunistically update it
Message-ID: <20140410115743.GA1446@abyss.utx.wifi>
In-Reply-To: <CACsJy8D9dsxOA6xVmhxa7N20OxEQ1a63rQm6QCtwq9ThG6E3RA@mail.gmail.com>

On Thu, Apr 10, 2014 at 05:40:55PM +0700, Duy Nguyen wrote:
> verify_hdr() is a bit expensive because you need to digest the whole
> index file (could big as big as 14MB on webkit). Could we get away
> without it? I mean, is it enough that we pick the last 20 bytes and
> compare it with istate->sha1? If we only need 20 bytes, pread() may be
> better than mmap().
> 
> The chance of SHA-1 collision is small enough for us to ignore, I
> think. And if a client updates the index without updating the trailing
> sha-1, the index is broken and we don't have to worry about
> overwriting it.

That's true, I will commit version 6 in a bit.