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| author | NeilBrown <neilb@cse.unsw.edu.au> | 2006-01-06 00:09:49 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-01-06 08:33:21 -0800 |
| commit | 1f1e030bf75774b6a283518e1534d598e14147d4 (patch) | |
| tree | 8b59e6ed6db756066d2cc18b35d00a753f13e237 /net | |
| parent | 4b2f0260c74324abca76ccaa42d426af163125e7 (diff) | |
| download | linux-1f1e030bf75774b6a283518e1534d598e14147d4.tar.gz | |
[PATCH] knfsd: fix hash function for IP addresses on 64bit little-endian machines.
The hash.h hash_long function, when used on a 64 bit machine, ignores many of the middle-order bits. (The prime chosen it too bit-sparse). IP addresses for clients of an NFS server are very likely to differ only in the low-order bits. As addresses are stored in network-byte-order, these bits become middle-order bits in a little-endian 64bit 'long', and so do not contribute to the hash. Thus you can have the situation where all clients appear on one hash chain. So, until hash_long is fixed (or maybe forever), us a hash function that works well on IP addresses - xor the bytes together. Thanks to "Iozone" <capps@iozone.org> for identifying this problem. Cc: "Iozone" <capps@iozone.org> Signed-off-by: Neil Brown <neilb@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/sunrpc/svcauth_unix.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c index cac2e774dd81..3e6c694bbad1 100644 --- a/net/sunrpc/svcauth_unix.c +++ b/net/sunrpc/svcauth_unix.c @@ -101,10 +101,22 @@ static void ip_map_put(struct cache_head *item, struct cache_detail *cd) } } +#if IP_HASHBITS == 8 +/* hash_long on a 64 bit machine is currently REALLY BAD for + * IP addresses in reverse-endian (i.e. on a little-endian machine). + * So use a trivial but reliable hash instead + */ +static inline int hash_ip(unsigned long ip) +{ + int hash = ip ^ (ip>>16); + return (hash ^ (hash>>8)) & 0xff; +} +#endif + static inline int ip_map_hash(struct ip_map *item) { return hash_str(item->m_class, IP_HASHBITS) ^ - hash_long((unsigned long)item->m_addr.s_addr, IP_HASHBITS); + hash_ip((unsigned long)item->m_addr.s_addr); } static inline int ip_map_match(struct ip_map *item, struct ip_map *tmp) { |