Merge branch 'hash' of git://ftp.sciencehorizons.net/linux
Pull string hash improvements from George Spelvin:
"This series does several related things:
- Makes the dcache hash (fs/namei.c) useful for general kernel use.
(Thanks to Bruce for noticing the zero-length corner case)
- Converts the string hashes in <linux/sunrpc/svcauth.h> to use the
above.
- Avoids 64-bit multiplies in hash_64() on 32-bit platforms. Two
32-bit multiplies will do well enough.
- Rids the world of the bad hash multipliers in hash_32.
This finishes the job started in commit 689de1d6ca95 ("Minimal
fix-up of bad hashing behavior of hash_64()")
The vast majority of Linux architectures have hardware support for
32x32-bit multiply and so derive no benefit from "simplified"
multipliers.
The few processors that do not (68000, h8/300 and some models of
Microblaze) have arch-specific implementations added. Those
patches are last in the series.
- Overhauls the dcache hash mixing.
The patch in commit 0fed3ac866ea ("namei: Improve hash mixing if
CONFIG_DCACHE_WORD_ACCESS") was an off-the-cuff suggestion.
Replaced with a much more careful design that's simultaneously
faster and better. (My own invention, as there was noting suitable
in the literature I could find. Comments welcome!)
- Modify the hash_name() loop to skip the initial HASH_MIX(). This
would let us salt the hash if we ever wanted to.
- Sort out partial_name_hash().
The hash function is declared as using a long state, even though
it's truncated to 32 bits at the end and the extra internal state
contributes nothing to the result. And some callers do odd things:
- fs/hfs/string.c only allocates 32 bits of state
- fs/hfsplus/unicode.c uses it to hash 16-bit unicode symbols not bytes
- Modify bytemask_from_count to handle inputs of 1..sizeof(long)
rather than 0..sizeof(long)-1. This would simplify users other
than full_name_hash"
Special thanks to Bruce Fields for testing and finding bugs in v1. (I
learned some humbling lessons about "obviously correct" code.)
On the arch-specific front, the m68k assembly has been tested in a
standalone test harness, I've been in contact with the Microblaze
maintainers who mostly don't care, as the hardware multiplier is never
omitted in real-world applications, and I haven't heard anything from
the H8/300 world"
* 'hash' of git://ftp.sciencehorizons.net/linux:
h8300: Add <asm/hash.h>
microblaze: Add <asm/hash.h>
m68k: Add <asm/hash.h>
<linux/hash.h>: Add support for architecture-specific functions
fs/namei.c: Improve dcache hash function
Eliminate bad hash multipliers from hash_32() and hash_64()
Change hash_64() return value to 32 bits
<linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string()
fs/namei.c: Add hashlen_string() function
Pull out string hash to <linux/stringhash.h>
diff --git a/arch/Kconfig b/arch/Kconfig
index b16e74e..d794384 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -598,6 +598,14 @@
Architecture supports the 'objtool check' host tool command, which
performs compile-time stack metadata validation.
+config HAVE_ARCH_HASH
+ bool
+ default n
+ help
+ If this is set, the architecture provides an <asm/hash.h>
+ file which provides platform-specific implementations of some
+ functions in <linux/hash.h> or fs/namei.c.
+
#
# ABI hall of shame
#
diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index aa232de2..3ae8525 100644
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -20,6 +20,7 @@
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZO
select HAVE_ARCH_KGDB
+ select HAVE_ARCH_HASH
select CPU_NO_EFFICIENT_FFS
config RWSEM_GENERIC_SPINLOCK
diff --git a/arch/h8300/include/asm/hash.h b/arch/h8300/include/asm/hash.h
new file mode 100644
index 0000000..04cfbd2
--- /dev/null
+++ b/arch/h8300/include/asm/hash.h
@@ -0,0 +1,53 @@
+#ifndef _ASM_HASH_H
+#define _ASM_HASH_H
+
+/*
+ * The later H8SX models have a 32x32-bit multiply, but the H8/300H
+ * and H8S have only 16x16->32. Since it's tolerably compact, this is
+ * basically an inlined version of the __mulsi3 code. Since the inputs
+ * are not expected to be small, it's also simplfied by skipping the
+ * early-out checks.
+ *
+ * (Since neither CPU has any multi-bit shift instructions, a
+ * shift-and-add version is a non-starter.)
+ *
+ * TODO: come up with an arch-specific version of the hashing in fs/namei.c,
+ * since that is heavily dependent on rotates. Which, as mentioned, suck
+ * horribly on H8.
+ */
+
+#if defined(CONFIG_CPU_H300H) || defined(CONFIG_CPU_H8S)
+
+#define HAVE_ARCH__HASH_32 1
+
+/*
+ * Multiply by k = 0x61C88647. Fitting this into three registers requires
+ * one extra instruction, but reducing register pressure will probably
+ * make that back and then some.
+ *
+ * GCC asm note: %e1 is the high half of operand %1, while %f1 is the
+ * low half. So if %1 is er4, then %e1 is e4 and %f1 is r4.
+ *
+ * This has been designed to modify x in place, since that's the most
+ * common usage, but preserve k, since hash_64() makes two calls in
+ * quick succession.
+ */
+static inline u32 __attribute_const__ __hash_32(u32 x)
+{
+ u32 temp;
+
+ asm( "mov.w %e1,%f0"
+ "\n mulxu.w %f2,%0" /* klow * xhigh */
+ "\n mov.w %f0,%e1" /* The extra instruction */
+ "\n mov.w %f1,%f0"
+ "\n mulxu.w %e2,%0" /* khigh * xlow */
+ "\n add.w %e1,%f0"
+ "\n mulxu.w %f2,%1" /* klow * xlow */
+ "\n add.w %f0,%e1"
+ : "=&r" (temp), "=r" (x)
+ : "%r" (GOLDEN_RATIO_32), "1" (x));
+ return x;
+}
+
+#endif
+#endif /* _ASM_HASH_H */
diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
index 8ace920..967260f 100644
--- a/arch/m68k/Kconfig.cpu
+++ b/arch/m68k/Kconfig.cpu
@@ -41,6 +41,7 @@
select CPU_HAS_NO_UNALIGNED
select GENERIC_CSUM
select CPU_NO_EFFICIENT_FFS
+ select HAVE_ARCH_HASH
help
The Freescale (was Motorola) 68000 CPU is the first generation of
the well known M68K family of processors. The CPU core as well as
diff --git a/arch/m68k/include/asm/hash.h b/arch/m68k/include/asm/hash.h
new file mode 100644
index 0000000..6407af8
--- /dev/null
+++ b/arch/m68k/include/asm/hash.h
@@ -0,0 +1,59 @@
+#ifndef _ASM_HASH_H
+#define _ASM_HASH_H
+
+/*
+ * If CONFIG_M68000=y (original mc68000/010), this file is #included
+ * to work around the lack of a MULU.L instruction.
+ */
+
+#define HAVE_ARCH__HASH_32 1
+/*
+ * While it would be legal to substitute a different hash operation
+ * entirely, let's keep it simple and just use an optimized multiply
+ * by GOLDEN_RATIO_32 = 0x61C88647.
+ *
+ * The best way to do that appears to be to multiply by 0x8647 with
+ * shifts and adds, and use mulu.w to multiply the high half by 0x61C8.
+ *
+ * Because the 68000 has multi-cycle shifts, this addition chain is
+ * chosen to minimise the shift distances.
+ *
+ * Despite every attempt to spoon-feed it simple operations, GCC
+ * 6.1.1 doggedly insists on doing annoying things like converting
+ * "lsl.l #2,<reg>" (12 cycles) to two adds (8+8 cycles).
+ *
+ * It also likes to notice two shifts in a row, like "a = x << 2" and
+ * "a <<= 7", and convert that to "a = x << 9". But shifts longer
+ * than 8 bits are extra-slow on m68k, so that's a lose.
+ *
+ * Since the 68000 is a very simple in-order processor with no
+ * instruction scheduling effects on execution time, we can safely
+ * take it out of GCC's hands and write one big asm() block.
+ *
+ * Without calling overhead, this operation is 30 bytes (14 instructions
+ * plus one immediate constant) and 166 cycles.
+ *
+ * (Because %2 is fetched twice, it can't be postincrement, and thus it
+ * can't be a fully general "g" or "m". Register is preferred, but
+ * offsettable memory or immediate will work.)
+ */
+static inline u32 __attribute_const__ __hash_32(u32 x)
+{
+ u32 a, b;
+
+ asm( "move.l %2,%0" /* a = x * 0x0001 */
+ "\n lsl.l #2,%0" /* a = x * 0x0004 */
+ "\n move.l %0,%1"
+ "\n lsl.l #7,%0" /* a = x * 0x0200 */
+ "\n add.l %2,%0" /* a = x * 0x0201 */
+ "\n add.l %0,%1" /* b = x * 0x0205 */
+ "\n add.l %0,%0" /* a = x * 0x0402 */
+ "\n add.l %0,%1" /* b = x * 0x0607 */
+ "\n lsl.l #5,%0" /* a = x * 0x8040 */
+ : "=&d,d" (a), "=&r,r" (b)
+ : "r,roi?" (x)); /* a+b = x*0x8647 */
+
+ return ((u16)(x*0x61c8) << 16) + a + b;
+}
+
+#endif /* _ASM_HASH_H */
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index f17c3a4..636e072 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -16,6 +16,7 @@
select GENERIC_IRQ_SHOW
select GENERIC_PCI_IOMAP
select GENERIC_SCHED_CLOCK
+ select HAVE_ARCH_HASH
select HAVE_ARCH_KGDB
select HAVE_DEBUG_KMEMLEAK
select HAVE_DMA_API_DEBUG
diff --git a/arch/microblaze/include/asm/hash.h b/arch/microblaze/include/asm/hash.h
new file mode 100644
index 0000000..753513a
--- /dev/null
+++ b/arch/microblaze/include/asm/hash.h
@@ -0,0 +1,81 @@
+#ifndef _ASM_HASH_H
+#define _ASM_HASH_H
+
+/*
+ * Fortunately, most people who want to run Linux on Microblaze enable
+ * both multiplier and barrel shifter, but omitting them is technically
+ * a supported configuration.
+ *
+ * With just a barrel shifter, we can implement an efficient constant
+ * multiply using shifts and adds. GCC can find a 9-step solution, but
+ * this 6-step solution was found by Yevgen Voronenko's implementation
+ * of the Hcub algorithm at http://spiral.ece.cmu.edu/mcm/gen.html.
+ *
+ * That software is really not designed for a single multiplier this large,
+ * but if you run it enough times with different seeds, it'll find several
+ * 6-shift, 6-add sequences for computing x * 0x61C88647. They are all
+ * c = (x << 19) + x;
+ * a = (x << 9) + c;
+ * b = (x << 23) + a;
+ * return (a<<11) + (b<<6) + (c<<3) - b;
+ * with variations on the order of the final add.
+ *
+ * Without even a shifter, it's hopless; any hash function will suck.
+ */
+
+#if CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL == 0
+
+#define HAVE_ARCH__HASH_32 1
+
+/* Multiply by GOLDEN_RATIO_32 = 0x61C88647 */
+static inline u32 __attribute_const__ __hash_32(u32 a)
+{
+#if CONFIG_XILINX_MICROBLAZE0_USE_BARREL
+ unsigned int b, c;
+
+ /* Phase 1: Compute three intermediate values */
+ b = a << 23;
+ c = (a << 19) + a;
+ a = (a << 9) + c;
+ b += a;
+
+ /* Phase 2: Compute (a << 11) + (b << 6) + (c << 3) - b */
+ a <<= 5;
+ a += b; /* (a << 5) + b */
+ a <<= 3;
+ a += c; /* (a << 8) + (b << 3) + c */
+ a <<= 3;
+ return a - b; /* (a << 11) + (b << 6) + (c << 3) - b */
+#else
+ /*
+ * "This is really going to hurt."
+ *
+ * Without a barrel shifter, left shifts are implemented as
+ * repeated additions, and the best we can do is an optimal
+ * addition-subtraction chain. This one is not known to be
+ * optimal, but at 37 steps, it's decent for a 31-bit multiplier.
+ *
+ * Question: given its size (37*4 = 148 bytes per instance),
+ * and slowness, is this worth having inline?
+ */
+ unsigned int b, c, d;
+
+ b = a << 4; /* 4 */
+ c = b << 1; /* 1 5 */
+ b += a; /* 1 6 */
+ c += b; /* 1 7 */
+ c <<= 3; /* 3 10 */
+ c -= a; /* 1 11 */
+ d = c << 7; /* 7 18 */
+ d += b; /* 1 19 */
+ d <<= 8; /* 8 27 */
+ d += a; /* 1 28 */
+ d <<= 1; /* 1 29 */
+ d += b; /* 1 30 */
+ d <<= 6; /* 6 36 */
+ return d + c; /* 1 37 total instructions*/
+#endif
+}
+
+#endif /* !CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL */
+#endif /* _ASM_HASH_H */
diff --git a/drivers/media/usb/dvb-usb-v2/af9015.c b/drivers/media/usb/dvb-usb-v2/af9015.c
index 95a7388..09e0f58 100644
--- a/drivers/media/usb/dvb-usb-v2/af9015.c
+++ b/drivers/media/usb/dvb-usb-v2/af9015.c
@@ -398,6 +398,8 @@
}
#define AF9015_EEPROM_SIZE 256
+/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
+#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
/* hash (and dump) eeprom */
static int af9015_eeprom_hash(struct dvb_usb_device *d)
diff --git a/fs/dcache.c b/fs/dcache.c
index c622872..ad4a542 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1670,8 +1670,7 @@
struct qstr q;
q.name = name;
- q.len = strlen(name);
- q.hash = full_name_hash(q.name, q.len);
+ q.hash_len = hashlen_string(name);
return d_alloc(parent, &q);
}
EXPORT_SYMBOL(d_alloc_name);
diff --git a/fs/namei.c b/fs/namei.c
index 15b124c..e7bf99d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -35,6 +35,7 @@
#include <linux/fs_struct.h>
#include <linux/posix_acl.h>
#include <linux/hash.h>
+#include <linux/bitops.h>
#include <asm/uaccess.h>
#include "internal.h"
@@ -1797,74 +1798,144 @@
#include <asm/word-at-a-time.h>
-#ifdef CONFIG_64BIT
+#ifdef HASH_MIX
-static inline unsigned int fold_hash(unsigned long hash)
-{
- return hash_64(hash, 32);
-}
+/* Architecture provides HASH_MIX and fold_hash() in <asm/hash.h> */
+
+#elif defined(CONFIG_64BIT)
+/*
+ * Register pressure in the mixing function is an issue, particularly
+ * on 32-bit x86, but almost any function requires one state value and
+ * one temporary. Instead, use a function designed for two state values
+ * and no temporaries.
+ *
+ * This function cannot create a collision in only two iterations, so
+ * we have two iterations to achieve avalanche. In those two iterations,
+ * we have six layers of mixing, which is enough to spread one bit's
+ * influence out to 2^6 = 64 state bits.
+ *
+ * Rotate constants are scored by considering either 64 one-bit input
+ * deltas or 64*63/2 = 2016 two-bit input deltas, and finding the
+ * probability of that delta causing a change to each of the 128 output
+ * bits, using a sample of random initial states.
+ *
+ * The Shannon entropy of the computed probabilities is then summed
+ * to produce a score. Ideally, any input change has a 50% chance of
+ * toggling any given output bit.
+ *
+ * Mixing scores (in bits) for (12,45):
+ * Input delta: 1-bit 2-bit
+ * 1 round: 713.3 42542.6
+ * 2 rounds: 2753.7 140389.8
+ * 3 rounds: 5954.1 233458.2
+ * 4 rounds: 7862.6 256672.2
+ * Perfect: 8192 258048
+ * (64*128) (64*63/2 * 128)
+ */
+#define HASH_MIX(x, y, a) \
+ ( x ^= (a), \
+ y ^= x, x = rol64(x,12),\
+ x += y, y = rol64(y,45),\
+ y *= 9 )
/*
- * This is George Marsaglia's XORSHIFT generator.
- * It implements a maximum-period LFSR in only a few
- * instructions. It also has the property (required
- * by hash_name()) that mix_hash(0) = 0.
+ * Fold two longs into one 32-bit hash value. This must be fast, but
+ * latency isn't quite as critical, as there is a fair bit of additional
+ * work done before the hash value is used.
*/
-static inline unsigned long mix_hash(unsigned long hash)
+static inline unsigned int fold_hash(unsigned long x, unsigned long y)
{
- hash ^= hash << 13;
- hash ^= hash >> 7;
- hash ^= hash << 17;
- return hash;
+ y ^= x * GOLDEN_RATIO_64;
+ y *= GOLDEN_RATIO_64;
+ return y >> 32;
}
#else /* 32-bit case */
-#define fold_hash(x) (x)
+/*
+ * Mixing scores (in bits) for (7,20):
+ * Input delta: 1-bit 2-bit
+ * 1 round: 330.3 9201.6
+ * 2 rounds: 1246.4 25475.4
+ * 3 rounds: 1907.1 31295.1
+ * 4 rounds: 2042.3 31718.6
+ * Perfect: 2048 31744
+ * (32*64) (32*31/2 * 64)
+ */
+#define HASH_MIX(x, y, a) \
+ ( x ^= (a), \
+ y ^= x, x = rol32(x, 7),\
+ x += y, y = rol32(y,20),\
+ y *= 9 )
-static inline unsigned long mix_hash(unsigned long hash)
+static inline unsigned int fold_hash(unsigned long x, unsigned long y)
{
- hash ^= hash << 13;
- hash ^= hash >> 17;
- hash ^= hash << 5;
- return hash;
+ /* Use arch-optimized multiply if one exists */
+ return __hash_32(y ^ __hash_32(x));
}
#endif
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/*
+ * Return the hash of a string of known length. This is carfully
+ * designed to match hash_name(), which is the more critical function.
+ * In particular, we must end by hashing a final word containing 0..7
+ * payload bytes, to match the way that hash_name() iterates until it
+ * finds the delimiter after the name.
+ */
+unsigned int full_name_hash(const char *name, unsigned int len)
{
- unsigned long a, hash = 0;
+ unsigned long a, x = 0, y = 0;
for (;;) {
+ if (!len)
+ goto done;
a = load_unaligned_zeropad(name);
if (len < sizeof(unsigned long))
break;
- hash = mix_hash(hash + a);
+ HASH_MIX(x, y, a);
name += sizeof(unsigned long);
len -= sizeof(unsigned long);
- if (!len)
- goto done;
}
- hash += a & bytemask_from_count(len);
+ x ^= a & bytemask_from_count(len);
done:
- return fold_hash(hash);
+ return fold_hash(x, y);
}
EXPORT_SYMBOL(full_name_hash);
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hashlen_string(const char *name)
+{
+ unsigned long a = 0, x = 0, y = 0, adata, mask, len;
+ const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+
+ len = -sizeof(unsigned long);
+ do {
+ HASH_MIX(x, y, a);
+ len += sizeof(unsigned long);
+ a = load_unaligned_zeropad(name+len);
+ } while (!has_zero(a, &adata, &constants));
+
+ adata = prep_zero_mask(a, adata, &constants);
+ mask = create_zero_mask(adata);
+ x ^= a & zero_bytemask(mask);
+
+ return hashlen_create(fold_hash(x, y), len + find_zero(mask));
+}
+EXPORT_SYMBOL(hashlen_string);
+
/*
* Calculate the length and hash of the path component, and
* return the "hash_len" as the result.
*/
static inline u64 hash_name(const char *name)
{
- unsigned long a, b, adata, bdata, mask, hash, len;
+ unsigned long a = 0, b, x = 0, y = 0, adata, bdata, mask, len;
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
- hash = a = 0;
len = -sizeof(unsigned long);
do {
- hash = mix_hash(hash + a);
+ HASH_MIX(x, y, a);
len += sizeof(unsigned long);
a = load_unaligned_zeropad(name+len);
b = a ^ REPEAT_BYTE('/');
@@ -1872,25 +1943,40 @@
adata = prep_zero_mask(a, adata, &constants);
bdata = prep_zero_mask(b, bdata, &constants);
-
mask = create_zero_mask(adata | bdata);
+ x ^= a & zero_bytemask(mask);
- hash += a & zero_bytemask(mask);
- len += find_zero(mask);
- return hashlen_create(fold_hash(hash), len);
+ return hashlen_create(fold_hash(x, y), len + find_zero(mask));
}
-#else
+#else /* !CONFIG_DCACHE_WORD_ACCESS: Slow, byte-at-a-time version */
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/* Return the hash of a string of known length */
+unsigned int full_name_hash(const char *name, unsigned int len)
{
unsigned long hash = init_name_hash();
while (len--)
- hash = partial_name_hash(*name++, hash);
+ hash = partial_name_hash((unsigned char)*name++, hash);
return end_name_hash(hash);
}
EXPORT_SYMBOL(full_name_hash);
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hash_string(const char *name)
+{
+ unsigned long hash = init_name_hash();
+ unsigned long len = 0, c;
+
+ c = (unsigned char)*name;
+ do {
+ len++;
+ hash = partial_name_hash(c, hash);
+ c = (unsigned char)name[len];
+ } while (c);
+ return hashlen_create(end_name_hash(hash), len);
+}
+EXPORT_SYMBOL(hash_string);
+
/*
* We know there's a real path component here of at least
* one character.
@@ -1934,7 +2020,7 @@
int type;
err = may_lookup(nd);
- if (err)
+ if (err)
return err;
hash_len = hash_name(name);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index f8506e8..484c879 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -10,6 +10,7 @@
#include <linux/cache.h>
#include <linux/rcupdate.h>
#include <linux/lockref.h>
+#include <linux/stringhash.h>
struct path;
struct vfsmount;
@@ -52,9 +53,6 @@
};
#define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
-#define hashlen_hash(hashlen) ((u32) (hashlen))
-#define hashlen_len(hashlen) ((u32)((hashlen) >> 32))
-#define hashlen_create(hash,len) (((u64)(len)<<32)|(u32)(hash))
struct dentry_stat_t {
long nr_dentry;
@@ -65,29 +63,6 @@
};
extern struct dentry_stat_t dentry_stat;
-/* Name hashing routines. Initial hash value */
-/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
-#define init_name_hash() 0
-
-/* partial hash update function. Assume roughly 4 bits per character */
-static inline unsigned long
-partial_name_hash(unsigned long c, unsigned long prevhash)
-{
- return (prevhash + (c << 4) + (c >> 4)) * 11;
-}
-
-/*
- * Finally: cut down the number of bits to a int value (and try to avoid
- * losing bits)
- */
-static inline unsigned long end_name_hash(unsigned long hash)
-{
- return (unsigned int) hash;
-}
-
-/* Compute the hash for a name string. */
-extern unsigned int full_name_hash(const unsigned char *, unsigned int);
-
/*
* Try to keep struct dentry aligned on 64 byte cachelines (this will
* give reasonable cacheline footprint with larger lines without the
diff --git a/include/linux/hash.h b/include/linux/hash.h
index 79c52fa..ad6fa21 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -3,92 +3,94 @@
/* Fast hashing routine for ints, longs and pointers.
(C) 2002 Nadia Yvette Chambers, IBM */
-/*
- * Knuth recommends primes in approximately golden ratio to the maximum
- * integer representable by a machine word for multiplicative hashing.
- * Chuck Lever verified the effectiveness of this technique:
- * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
- *
- * These primes are chosen to be bit-sparse, that is operations on
- * them can use shifts and additions instead of multiplications for
- * machines where multiplications are slow.
- */
-
#include <asm/types.h>
#include <linux/compiler.h>
-/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
-#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
-/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
-#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
-
+/*
+ * The "GOLDEN_RATIO_PRIME" is used in ifs/btrfs/brtfs_inode.h and
+ * fs/inode.c. It's not actually prime any more (the previous primes
+ * were actively bad for hashing), but the name remains.
+ */
#if BITS_PER_LONG == 32
-#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_32
#define hash_long(val, bits) hash_32(val, bits)
#elif BITS_PER_LONG == 64
#define hash_long(val, bits) hash_64(val, bits)
-#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_64
#else
#error Wordsize not 32 or 64
#endif
/*
- * The above primes are actively bad for hashing, since they are
- * too sparse. The 32-bit one is mostly ok, the 64-bit one causes
- * real problems. Besides, the "prime" part is pointless for the
- * multiplicative hash.
+ * This hash multiplies the input by a large odd number and takes the
+ * high bits. Since multiplication propagates changes to the most
+ * significant end only, it is essential that the high bits of the
+ * product be used for the hash value.
+ *
+ * Chuck Lever verified the effectiveness of this technique:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
*
* Although a random odd number will do, it turns out that the golden
* ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
- * properties.
+ * properties. (See Knuth vol 3, section 6.4, exercise 9.)
*
- * These are the negative, (1 - phi) = (phi^2) = (3 - sqrt(5))/2.
- * (See Knuth vol 3, section 6.4, exercise 9.)
+ * These are the negative, (1 - phi) = phi**2 = (3 - sqrt(5))/2,
+ * which is very slightly easier to multiply by and makes no
+ * difference to the hash distribution.
*/
#define GOLDEN_RATIO_32 0x61C88647
#define GOLDEN_RATIO_64 0x61C8864680B583EBull
-static __always_inline u64 hash_64(u64 val, unsigned int bits)
-{
- u64 hash = val;
-
-#if BITS_PER_LONG == 64
- hash = hash * GOLDEN_RATIO_64;
-#else
- /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
- u64 n = hash;
- n <<= 18;
- hash -= n;
- n <<= 33;
- hash -= n;
- n <<= 3;
- hash += n;
- n <<= 3;
- hash -= n;
- n <<= 4;
- hash += n;
- n <<= 2;
- hash += n;
+#ifdef CONFIG_HAVE_ARCH_HASH
+/* This header may use the GOLDEN_RATIO_xx constants */
+#include <asm/hash.h>
#endif
- /* High bits are more random, so use them. */
- return hash >> (64 - bits);
-}
-
-static inline u32 hash_32(u32 val, unsigned int bits)
+/*
+ * The _generic versions exist only so lib/test_hash.c can compare
+ * the arch-optimized versions with the generic.
+ *
+ * Note that if you change these, any <asm/hash.h> that aren't updated
+ * to match need to have their HAVE_ARCH_* define values updated so the
+ * self-test will not false-positive.
+ */
+#ifndef HAVE_ARCH__HASH_32
+#define __hash_32 __hash_32_generic
+#endif
+static inline u32 __hash_32_generic(u32 val)
{
- /* On some cpus multiply is faster, on others gcc will do shifts */
- u32 hash = val * GOLDEN_RATIO_PRIME_32;
-
- /* High bits are more random, so use them. */
- return hash >> (32 - bits);
+ return val * GOLDEN_RATIO_32;
}
-static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
+#ifndef HAVE_ARCH_HASH_32
+#define hash_32 hash_32_generic
+#endif
+static inline u32 hash_32_generic(u32 val, unsigned int bits)
+{
+ /* High bits are more random, so use them. */
+ return __hash_32(val) >> (32 - bits);
+}
+
+#ifndef HAVE_ARCH_HASH_64
+#define hash_64 hash_64_generic
+#endif
+static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
+{
+#if BITS_PER_LONG == 64
+ /* 64x64-bit multiply is efficient on all 64-bit processors */
+ return val * GOLDEN_RATIO_64 >> (64 - bits);
+#else
+ /* Hash 64 bits using only 32x32-bit multiply. */
+ return hash_32((u32)val ^ __hash_32(val >> 32), bits);
+#endif
+}
+
+static inline u32 hash_ptr(const void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);
}
+/* This really should be called fold32_ptr; it does no hashing to speak of. */
static inline u32 hash32_ptr(const void *ptr)
{
unsigned long val = (unsigned long)ptr;
diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h
new file mode 100644
index 0000000..451771d
--- /dev/null
+++ b/include/linux/stringhash.h
@@ -0,0 +1,76 @@
+#ifndef __LINUX_STRINGHASH_H
+#define __LINUX_STRINGHASH_H
+
+#include <linux/compiler.h> /* For __pure */
+#include <linux/types.h> /* For u32, u64 */
+
+/*
+ * Routines for hashing strings of bytes to a 32-bit hash value.
+ *
+ * These hash functions are NOT GUARANTEED STABLE between kernel
+ * versions, architectures, or even repeated boots of the same kernel.
+ * (E.g. they may depend on boot-time hardware detection or be
+ * deliberately randomized.)
+ *
+ * They are also not intended to be secure against collisions caused by
+ * malicious inputs; much slower hash functions are required for that.
+ *
+ * They are optimized for pathname components, meaning short strings.
+ * Even if a majority of files have longer names, the dynamic profile of
+ * pathname components skews short due to short directory names.
+ * (E.g. /usr/lib/libsesquipedalianism.so.3.141.)
+ */
+
+/*
+ * Version 1: one byte at a time. Example of use:
+ *
+ * unsigned long hash = init_name_hash;
+ * while (*p)
+ * hash = partial_name_hash(tolower(*p++), hash);
+ * hash = end_name_hash(hash);
+ *
+ * Although this is designed for bytes, fs/hfsplus/unicode.c
+ * abuses it to hash 16-bit values.
+ */
+
+/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
+#define init_name_hash() 0
+
+/* partial hash update function. Assume roughly 4 bits per character */
+static inline unsigned long
+partial_name_hash(unsigned long c, unsigned long prevhash)
+{
+ return (prevhash + (c << 4) + (c >> 4)) * 11;
+}
+
+/*
+ * Finally: cut down the number of bits to a int value (and try to avoid
+ * losing bits)
+ */
+static inline unsigned long end_name_hash(unsigned long hash)
+{
+ return (unsigned int)hash;
+}
+
+/*
+ * Version 2: One word (32 or 64 bits) at a time.
+ * If CONFIG_DCACHE_WORD_ACCESS is defined (meaning <asm/word-at-a-time.h>
+ * exists, which describes major Linux platforms like x86 and ARM), then
+ * this computes a different hash function much faster.
+ *
+ * If not set, this falls back to a wrapper around the preceding.
+ */
+extern unsigned int __pure full_name_hash(const char *, unsigned int);
+
+/*
+ * A hash_len is a u64 with the hash of a string in the low
+ * half and the length in the high half.
+ */
+#define hashlen_hash(hashlen) ((u32)(hashlen))
+#define hashlen_len(hashlen) ((u32)((hashlen) >> 32))
+#define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash))
+
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+extern u64 __pure hashlen_string(const char *name);
+
+#endif /* __LINUX_STRINGHASH_H */
diff --git a/include/linux/sunrpc/svcauth.h b/include/linux/sunrpc/svcauth.h
index c00f53a..91d5a5d 100644
--- a/include/linux/sunrpc/svcauth.h
+++ b/include/linux/sunrpc/svcauth.h
@@ -16,6 +16,7 @@
#include <linux/sunrpc/cache.h>
#include <linux/sunrpc/gss_api.h>
#include <linux/hash.h>
+#include <linux/stringhash.h>
#include <linux/cred.h>
struct svc_cred {
@@ -165,41 +166,18 @@
extern int unix_gid_cache_create(struct net *net);
extern void unix_gid_cache_destroy(struct net *net);
-static inline unsigned long hash_str(char *name, int bits)
+/*
+ * The <stringhash.h> functions are good enough that we don't need to
+ * use hash_32() on them; just extracting the high bits is enough.
+ */
+static inline unsigned long hash_str(char const *name, int bits)
{
- unsigned long hash = 0;
- unsigned long l = 0;
- int len = 0;
- unsigned char c;
- do {
- if (unlikely(!(c = *name++))) {
- c = (char)len; len = -1;
- }
- l = (l << 8) | c;
- len++;
- if ((len & (BITS_PER_LONG/8-1))==0)
- hash = hash_long(hash^l, BITS_PER_LONG);
- } while (len);
- return hash >> (BITS_PER_LONG - bits);
+ return hashlen_hash(hashlen_string(name)) >> (32 - bits);
}
-static inline unsigned long hash_mem(char *buf, int length, int bits)
+static inline unsigned long hash_mem(char const *buf, int length, int bits)
{
- unsigned long hash = 0;
- unsigned long l = 0;
- int len = 0;
- unsigned char c;
- do {
- if (len == length) {
- c = (char)len; len = -1;
- } else
- c = *buf++;
- l = (l << 8) | c;
- len++;
- if ((len & (BITS_PER_LONG/8-1))==0)
- hash = hash_long(hash^l, BITS_PER_LONG);
- } while (len);
- return hash >> (BITS_PER_LONG - bits);
+ return full_name_hash(buf, length) >> (32 - bits);
}
#endif /* __KERNEL__ */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e707ab3..77d7d03 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1849,6 +1849,17 @@
If unsure, say N.
+config TEST_HASH
+ tristate "Perform selftest on hash functions"
+ default n
+ help
+ Enable this option to test the kernel's integer (<linux/hash,h>)
+ and string (<linux/stringhash.h>) hash functions on boot
+ (or module load).
+
+ This is intended to help people writing architecture-specific
+ optimized versions. If unsure, say N.
+
endmenu # runtime tests
config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index 42b6918..499fb35 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -48,6 +48,7 @@
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o
obj-$(CONFIG_TEST_KASAN) += test_kasan.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/test_hash.c b/lib/test_hash.c
new file mode 100644
index 0000000..c9549c8
--- /dev/null
+++ b/lib/test_hash.c
@@ -0,0 +1,250 @@
+/*
+ * Test cases for <linux/hash.h> and <linux/stringhash.h>
+ * This just verifies that various ways of computing a hash
+ * produce the same thing and, for cases where a k-bit hash
+ * value is requested, is of the requested size.
+ *
+ * We fill a buffer with a 255-byte null-terminated string,
+ * and use both full_name_hash() and hashlen_string() to hash the
+ * substrings from i to j, where 0 <= i < j < 256.
+ *
+ * The returned values are used to check that __hash_32() and
+ * __hash_32_generic() compute the same thing. Likewise hash_32()
+ * and hash_64().
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt "\n"
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/hash.h>
+#include <linux/stringhash.h>
+#include <linux/printk.h>
+
+/* 32-bit XORSHIFT generator. Seed must not be zero. */
+static u32 __init __attribute_const__
+xorshift(u32 seed)
+{
+ seed ^= seed << 13;
+ seed ^= seed >> 17;
+ seed ^= seed << 5;
+ return seed;
+}
+
+/* Given a non-zero x, returns a non-zero byte. */
+static u8 __init __attribute_const__
+mod255(u32 x)
+{
+ x = (x & 0xffff) + (x >> 16); /* 1 <= x <= 0x1fffe */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x2fd */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x100 */
+ x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0xff */
+ return x;
+}
+
+/* Fill the buffer with non-zero bytes. */
+static void __init
+fill_buf(char *buf, size_t len, u32 seed)
+{
+ size_t i;
+
+ for (i = 0; i < len; i++) {
+ seed = xorshift(seed);
+ buf[i] = mod255(seed);
+ }
+}
+
+/*
+ * Test the various integer hash functions. h64 (or its low-order bits)
+ * is the integer to hash. hash_or accumulates the OR of the hash values,
+ * which are later checked to see that they cover all the requested bits.
+ *
+ * Because these functions (as opposed to the string hashes) are all
+ * inline, the code being tested is actually in the module, and you can
+ * recompile and re-test the module without rebooting.
+ */
+static bool __init
+test_int_hash(unsigned long long h64, u32 hash_or[2][33])
+{
+ int k;
+ u32 h0 = (u32)h64, h1, h2;
+
+ /* Test __hash32 */
+ hash_or[0][0] |= h1 = __hash_32(h0);
+#ifdef HAVE_ARCH__HASH_32
+ hash_or[1][0] |= h2 = __hash_32_generic(h0);
+#if HAVE_ARCH__HASH_32 == 1
+ if (h1 != h2) {
+ pr_err("__hash_32(%#x) = %#x != __hash_32_generic() = %#x",
+ h0, h1, h2);
+ return false;
+ }
+#endif
+#endif
+
+ /* Test k = 1..32 bits */
+ for (k = 1; k <= 32; k++) {
+ u32 const m = ((u32)2 << (k-1)) - 1; /* Low k bits set */
+
+ /* Test hash_32 */
+ hash_or[0][k] |= h1 = hash_32(h0, k);
+ if (h1 > m) {
+ pr_err("hash_32(%#x, %d) = %#x > %#x", h0, k, h1, m);
+ return false;
+ }
+#ifdef HAVE_ARCH_HASH_32
+ h2 = hash_32_generic(h0, k);
+#if HAVE_ARCH_HASH_32 == 1
+ if (h1 != h2) {
+ pr_err("hash_32(%#x, %d) = %#x != hash_32_generic() "
+ " = %#x", h0, k, h1, h2);
+ return false;
+ }
+#else
+ if (h2 > m) {
+ pr_err("hash_32_generic(%#x, %d) = %#x > %#x",
+ h0, k, h1, m);
+ return false;
+ }
+#endif
+#endif
+ /* Test hash_64 */
+ hash_or[1][k] |= h1 = hash_64(h64, k);
+ if (h1 > m) {
+ pr_err("hash_64(%#llx, %d) = %#x > %#x", h64, k, h1, m);
+ return false;
+ }
+#ifdef HAVE_ARCH_HASH_64
+ h2 = hash_64_generic(h64, k);
+#if HAVE_ARCH_HASH_64 == 1
+ if (h1 != h2) {
+ pr_err("hash_64(%#llx, %d) = %#x != hash_64_generic() "
+ "= %#x", h64, k, h1, h2);
+ return false;
+ }
+#else
+ if (h2 > m) {
+ pr_err("hash_64_generic(%#llx, %d) = %#x > %#x",
+ h64, k, h1, m);
+ return false;
+ }
+#endif
+#endif
+ }
+
+ (void)h2; /* Suppress unused variable warning */
+ return true;
+}
+
+#define SIZE 256 /* Run time is cubic in SIZE */
+
+static int __init
+test_hash_init(void)
+{
+ char buf[SIZE+1];
+ u32 string_or = 0, hash_or[2][33] = { 0 };
+ unsigned tests = 0;
+ unsigned long long h64 = 0;
+ int i, j;
+
+ fill_buf(buf, SIZE, 1);
+
+ /* Test every possible non-empty substring in the buffer. */
+ for (j = SIZE; j > 0; --j) {
+ buf[j] = '\0';
+
+ for (i = 0; i <= j; i++) {
+ u64 hashlen = hashlen_string(buf+i);
+ u32 h0 = full_name_hash(buf+i, j-i);
+
+ /* Check that hashlen_string gets the length right */
+ if (hashlen_len(hashlen) != j-i) {
+ pr_err("hashlen_string(%d..%d) returned length"
+ " %u, expected %d",
+ i, j, hashlen_len(hashlen), j-i);
+ return -EINVAL;
+ }
+ /* Check that the hashes match */
+ if (hashlen_hash(hashlen) != h0) {
+ pr_err("hashlen_string(%d..%d) = %08x != "
+ "full_name_hash() = %08x",
+ i, j, hashlen_hash(hashlen), h0);
+ return -EINVAL;
+ }
+
+ string_or |= h0;
+ h64 = h64 << 32 | h0; /* For use with hash_64 */
+ if (!test_int_hash(h64, hash_or))
+ return -EINVAL;
+ tests++;
+ } /* i */
+ } /* j */
+
+ /* The OR of all the hash values should cover all the bits */
+ if (~string_or) {
+ pr_err("OR of all string hash results = %#x != %#x",
+ string_or, -1u);
+ return -EINVAL;
+ }
+ if (~hash_or[0][0]) {
+ pr_err("OR of all __hash_32 results = %#x != %#x",
+ hash_or[0][0], -1u);
+ return -EINVAL;
+ }
+#ifdef HAVE_ARCH__HASH_32
+#if HAVE_ARCH__HASH_32 != 1 /* Test is pointless if results match */
+ if (~hash_or[1][0]) {
+ pr_err("OR of all __hash_32_generic results = %#x != %#x",
+ hash_or[1][0], -1u);
+ return -EINVAL;
+ }
+#endif
+#endif
+
+ /* Likewise for all the i-bit hash values */
+ for (i = 1; i <= 32; i++) {
+ u32 const m = ((u32)2 << (i-1)) - 1; /* Low i bits set */
+
+ if (hash_or[0][i] != m) {
+ pr_err("OR of all hash_32(%d) results = %#x "
+ "(%#x expected)", i, hash_or[0][i], m);
+ return -EINVAL;
+ }
+ if (hash_or[1][i] != m) {
+ pr_err("OR of all hash_64(%d) results = %#x "
+ "(%#x expected)", i, hash_or[1][i], m);
+ return -EINVAL;
+ }
+ }
+
+ /* Issue notices about skipped tests. */
+#ifndef HAVE_ARCH__HASH_32
+ pr_info("__hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH__HASH_32 != 1
+ pr_info("__hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_32
+ pr_info("hash_32() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_32 != 1
+ pr_info("hash_32() is arch-specific; not compared to generic.");
+#endif
+#ifndef HAVE_ARCH_HASH_64
+ pr_info("hash_64() has no arch implementation to test.");
+#elif HAVE_ARCH_HASH_64 != 1
+ pr_info("hash_64() is arch-specific; not compared to generic.");
+#endif
+
+ pr_notice("%u tests passed.", tests);
+
+ return 0;
+}
+
+static void __exit test_hash_exit(void)
+{
+}
+
+module_init(test_hash_init); /* Does everything */
+module_exit(test_hash_exit); /* Does nothing */
+
+MODULE_LICENSE("GPL");
