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e8a07c9d22
Implement a function to generate hashes. It needs to be stable over time and endianness-independent as the hashes will appear on disk in future patches. It can assume that its input is a multiple of four bytes in size and alignment. This is borrowed from the VFS and simplified. le32_to_cpu() is added to make it endianness-independent. Changes ======= ver #3: - Read the data being hashed in an endianness-independent way[1]. - Change the size parameter to be in bytes rather than words. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [1] Link: https://lore.kernel.org/r/163819586113.215744.1699465806130102367.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906888735.143852.10944614318596881429.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967082342.1823006.8915671045444488742.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021493624.640689.9990442668811178628.stgit@warthog.procyon.org.uk/ # v4
106 lines
2.3 KiB
C
106 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* General filesystem local caching manager
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*
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* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#define FSCACHE_DEBUG_LEVEL CACHE
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#include <linux/module.h>
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#include <linux/init.h>
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#define CREATE_TRACE_POINTS
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#include "internal.h"
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MODULE_DESCRIPTION("FS Cache Manager");
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MODULE_AUTHOR("Red Hat, Inc.");
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MODULE_LICENSE("GPL");
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unsigned fscache_debug;
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module_param_named(debug, fscache_debug, uint,
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S_IWUSR | S_IRUGO);
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MODULE_PARM_DESC(fscache_debug,
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"FS-Cache debugging mask");
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struct workqueue_struct *fscache_wq;
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EXPORT_SYMBOL(fscache_wq);
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/*
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* Mixing scores (in bits) for (7,20):
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* Input delta: 1-bit 2-bit
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* 1 round: 330.3 9201.6
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* 2 rounds: 1246.4 25475.4
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* 3 rounds: 1907.1 31295.1
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* 4 rounds: 2042.3 31718.6
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* Perfect: 2048 31744
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* (32*64) (32*31/2 * 64)
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*/
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#define HASH_MIX(x, y, a) \
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( x ^= (a), \
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y ^= x, x = rol32(x, 7),\
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x += y, y = rol32(y,20),\
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y *= 9 )
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static inline unsigned int fold_hash(unsigned long x, unsigned long y)
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{
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/* Use arch-optimized multiply if one exists */
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return __hash_32(y ^ __hash_32(x));
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}
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/*
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* Generate a hash. This is derived from full_name_hash(), but we want to be
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* sure it is arch independent and that it doesn't change as bits of the
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* computed hash value might appear on disk. The caller must guarantee that
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* the source data is a multiple of four bytes in size.
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*/
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unsigned int fscache_hash(unsigned int salt, const void *data, size_t len)
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{
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const __le32 *p = data;
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unsigned int a, x = 0, y = salt, n = len / sizeof(__le32);
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for (; n; n--) {
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a = le32_to_cpu(*p++);
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HASH_MIX(x, y, a);
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}
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return fold_hash(x, y);
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}
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/*
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* initialise the fs caching module
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*/
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static int __init fscache_init(void)
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{
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int ret = -ENOMEM;
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fscache_wq = alloc_workqueue("fscache", WQ_UNBOUND | WQ_FREEZABLE, 0);
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if (!fscache_wq)
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goto error_wq;
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ret = fscache_proc_init();
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if (ret < 0)
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goto error_proc;
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pr_notice("Loaded\n");
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return 0;
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error_proc:
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destroy_workqueue(fscache_wq);
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error_wq:
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return ret;
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}
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fs_initcall(fscache_init);
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/*
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* clean up on module removal
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*/
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static void __exit fscache_exit(void)
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{
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_enter("");
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fscache_proc_cleanup();
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destroy_workqueue(fscache_wq);
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pr_notice("Unloaded\n");
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}
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module_exit(fscache_exit);
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