Is protection against hash DoS important for local on-disk format? I can't come up with a scenario, but maybe there is one. The kinds of DoS contemplated are really Google-scale, not really at the scale of ext4 directories, imo. I ask because if hash perf is the main goal here, then CityHash and particularly SpookyHash are better candidates. The latter has good performance even on legacy ARMv5 hardware. +Reardon ---------------------------------------- > Date: Sun, 21 Sep 2014 17:04:16 -0400 > From: linux@xxxxxxxxxxx > To: linux@xxxxxxxxxxx; tytso@xxxxxxx > Subject: Re: [RFC] mke2fs -E hash_alg=siphash: any interest? > CC: linux-ext4@xxxxxxxxxxxxxxx > >> I'm certainly not against adding a new hash function. The reality is >> that it would be quite a while before we could turn it on by default, >> because of the backwards compatibility concerns. > > Well, yes, obviously! My itch is just that I want to use it myself; > I prefer it for security and cleanliness reasons. The benchmarks are > mostly to prove that it isn't slower. > >> The question I would ask is whether we can show an anctual performance >> improvement with the hash being used in situ. > > I quite agree, but I'll have to have a working patch before such > a test can be made. > > One things I'm coming across immediately that I have to ask for > design guidance on is the hash algorithm number assignment: > > - Should I leave room for more hashes with a signed/unsigned distinction, > or should I assume that's a historical kludge that won't be perpetuated? > SipHash is defined on a byte string, so there isn't really a signed > version. > - Should I use a new EXT2_HASH_SIPHASH_62 = 6, or should I > renumber the (internal-only) EXT2_HASH_*_UNSIGNED values and use > EXT2_HASH_SIPHASH_4_2 = 4? > > None of this is truly final, but it would make my life easier if I > didn't have to change it on my test filesystems too often. > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
