mirror of
https://gitlab.freedesktop.org/NetworkManager/NetworkManager.git
synced 2025-12-24 06:40:16 +01:00
ee76b0979f
siphash24() is wildly used by projects nowadays. It's certainly slower then our djb hashing that we used before. But quite likely it's fast enough for us, given how wildly it is used. I think it would be hard to profile NetworkManager to show that the performance of hash tables is the issue, be it with djb or siphash24. Certainly with siphash24() it's much harder to exploit the hashing algorithm to cause worst case hash operations (provided that the seed is kept private). Does this better resistance against a denial of service matter for us? Probably not, but let's better be safe then sorry. Note that systemd's implementation uses a different seed for each hash table (at least, after the hash table grows to a certain size). We don't do that and use only one global seed.
129 lines
3.5 KiB
C
129 lines
3.5 KiB
C
/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
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/* NetworkManager -- Network link manager
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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* Boston, MA 02110-1301 USA.
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*
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* (C) Copyright 2017 Red Hat, Inc.
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*/
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#ifndef __NM_HASH_UTILS_H__
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#define __NM_HASH_UTILS_H__
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#include "siphash24.h"
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typedef struct {
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struct siphash _state;
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} NMHashState;
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void nm_hash_init (NMHashState *state, guint static_seed);
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static inline guint
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nm_hash_complete (NMHashState *state)
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{
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guint64 h;
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nm_assert (state);
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h = siphash24_finalize (&state->_state);
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/* we don't ever want to return a zero hash.
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*
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* NMPObject requires that in _idx_obj_part(), and it's just a good idea. */
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return (((guint) (h >> 32)) ^ ((guint) h)) ?: 1396707757u;
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}
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static inline void
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nm_hash_update (NMHashState *state, const void *ptr, gsize n)
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{
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nm_assert (state);
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nm_assert (ptr);
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nm_assert (n > 0);
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siphash24_compress (ptr, n, &state->_state);
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}
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static inline void
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nm_hash_update_uint (NMHashState *state, guint val)
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{
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nm_hash_update (state, &val, sizeof (val));
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}
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static inline void
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nm_hash_update_uint64 (NMHashState *state, guint64 val)
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{
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nm_hash_update (state, &val, sizeof (val));
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}
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static inline void
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nm_hash_update_ptr (NMHashState *state, gconstpointer ptr)
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{
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nm_hash_update (state, &ptr, sizeof (ptr));
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}
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static inline void
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nm_hash_update_mem (NMHashState *state, const void *ptr, gsize n)
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{
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/* This also hashes the length of the data. That means,
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* hashing two consecutive binary fields (of arbitrary
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* length), will hash differently. That is,
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* [[1,1], []] differs from [[1],[1]].
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*
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* If you have a constant length (sizeof), use nm_hash_update()
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* instead. */
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nm_hash_update (state, &n, sizeof (n));
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if (n > 0)
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siphash24_compress (ptr, n, &state->_state);
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}
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static inline void
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nm_hash_update_str0 (NMHashState *state, const char *str)
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{
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if (str)
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nm_hash_update_mem (state, str, strlen (str));
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else {
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gsize n = G_MAXSIZE;
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nm_hash_update (state, &n, sizeof (n));
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}
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}
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static inline void
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nm_hash_update_str (NMHashState *state, const char *str)
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{
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nm_assert (str);
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nm_hash_update (state, str, strlen (str) + 1);
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}
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#if _NM_CC_SUPPORT_GENERIC
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/* Like nm_hash_update_str(), but restricted to arrays only. nm_hash_update_str() only works
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* with a @str argument that cannot be NULL. If you have a string pointer, that is never NULL, use
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* nm_hash_update() instead. */
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#define nm_hash_update_strarr(state, str) \
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(_Generic (&(str), \
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const char (*) [sizeof (str)]: nm_hash_update_str ((state), (str)), \
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char (*) [sizeof (str)]: nm_hash_update_str ((state), (str))) \
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)
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#else
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#define nm_hash_update_strarr(state, str) nm_hash_update_str ((state), (str))
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#endif
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guint nm_hash_ptr (gconstpointer ptr);
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guint nm_direct_hash (gconstpointer str);
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guint nm_hash_str (const char *str);
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guint nm_str_hash (gconstpointer str);
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#endif /* __NM_HASH_UTILS_H__ */
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