#include "tdb_private.h"
#include <limits.h>
-/*
- For each value, we flip F bits in a bitmap of size 2^B. So we can think
- of this as a F*B bit hash (this isn't quite true due to hash collisions,
- but it seems good enough for F << B).
-
- Assume that we only have a single error; this is *not* the birthday
- problem, since the question is: "does that error hash to the same as
- the correct value", ie. a simple 1 in 2^F*B. The chances of detecting
- multiple errors is even higher (since we only need to detect one of
- them).
-
- Given that ldb uses a hash size of 10000, using 512 bytes per hash chain
- (5M) seems reasonable. With 128 hashes, that's about 1 in a million chance
- of missing a single linked list error.
-*/
-#define NUM_HASHES 128
-#define BITMAP_BITS (512 * CHAR_BIT)
-
-/* We use the excellent Jenkins lookup3 hash; this is based on hash_word2.
- * See: http://burtleburtle.net/bob/c/lookup3.c
- */
-#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
-
-#define final(a,b,c) \
-{ \
- c ^= b; c -= rot(b,14); \
- a ^= c; a -= rot(c,11); \
- b ^= a; b -= rot(a,25); \
- c ^= b; c -= rot(b,16); \
- a ^= c; a -= rot(c,4); \
- b ^= a; b -= rot(a,14); \
- c ^= b; c -= rot(b,24); \
-}
-
-static void hash(uint32_t key, uint32_t *pc, uint32_t *pb)
-{
- uint32_t a,b,c;
-
- /* Set up the internal state */
- a = b = c = 0xdeadbeef + *pc;
- c += *pb;
-
- a += key;
- final(a,b,c);
- *pc=c; *pb=b;
-}
-
-static void bit_flip(unsigned char bits[], unsigned int idx)
-{
- bits[idx / CHAR_BIT] ^= (1 << (idx % CHAR_BIT));
-}
-
-static void add_to_hash(unsigned char bits[], tdb_off_t off)
-{
- uint32_t h1 = off, h2 = 0;
- unsigned int i;
- for (i = 0; i < NUM_HASHES / 2; i++) {
- hash(off, &h1, &h2);
- bit_flip(bits, h1 % BITMAP_BITS);
- bit_flip(bits, h2 % BITMAP_BITS);
- h2++;
- }
-}
-
/* Since we opened it, these shouldn't fail unless it's recent corruption. */
static bool tdb_check_header(struct tdb_context *tdb, tdb_off_t *recovery)
{
return false;
}
+/* Generic record header check. */
static bool tdb_check_record(struct tdb_context *tdb,
tdb_off_t off,
const struct list_struct *rec)
return false;
}
-static TDB_DATA get_data(struct tdb_context *tdb, tdb_off_t off, tdb_len_t len)
+/* Grab some bytes: may copy if can't use mmap.
+ Caller has already done bounds check. */
+static TDB_DATA get_bytes(struct tdb_context *tdb,
+ tdb_off_t off, tdb_len_t len)
{
TDB_DATA d;
d.dsize = len;
- /* We've already done bounds check here. */
if (tdb->transaction == NULL && tdb->map_ptr != NULL)
d.dptr = (unsigned char *)tdb->map_ptr + off;
else
return d;
}
-static void put_data(struct tdb_context *tdb, TDB_DATA d)
+/* Frees data if we're not able to simply use mmap. */
+static void put_bytes(struct tdb_context *tdb, TDB_DATA d)
{
if (tdb->transaction == NULL && tdb->map_ptr != NULL)
return;
free(d.dptr);
}
+/* We use the excellent Jenkins lookup3 hash; this is based on hash_word2.
+ * See: http://burtleburtle.net/bob/c/lookup3.c
+ */
+#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
+static void hash(uint32_t key, uint32_t *pc, uint32_t *pb)
+{
+ uint32_t a,b,c;
+
+ /* Set up the internal state */
+ a = b = c = 0xdeadbeef + *pc;
+ c += *pb;
+ a += key;
+ c ^= b; c -= rot(b,14);
+ a ^= c; a -= rot(c,11);
+ b ^= a; b -= rot(a,25);
+ c ^= b; c -= rot(b,16);
+ a ^= c; a -= rot(c,4);
+ b ^= a; b -= rot(a,14);
+ c ^= b; c -= rot(b,24);
+ *pc=c; *pb=b;
+}
+
+/*
+ We want to check that all free records are in the free list
+ (only once), and all free list entries are free records. Similarly
+ for each hash chain of used records.
+
+ Doing that naively (without walking hash chains, since we want to be
+ linear) means keeping a list of records which have been seen in each
+ hash chain, and another of records pointed to (ie. next pointers
+ from records and the initial hash chain heads). These two lists
+ should be equal. This will take 8 bytes per record, and require
+ sorting at the end.
+
+ So instead, we record each offset in a bitmap such a way that
+ recording it twice will cancel out. Since each offset should appear
+ exactly twice, the bitmap should be zero at the end.
+
+ The approach was inspired by Bloom Filters (see Wikipedia). For
+ each value, we flip K bits in a bitmap of size N. The number of
+ distinct arrangements is:
+
+ N! / (K! * (N-K)!)
+
+ Of course, not all arrangements are actually distinct, but testing
+ shows this formula to be close enough.
+
+ So, if K == 8 and N == 256, the probability of two things flipping the same
+ bits is 1 in 409,663,695,276,000.
+
+ Given that ldb uses a hash size of 10000, using 32 bytes per hash chain
+ (320k) seems reasonable.
+*/
+#define NUM_HASHES 8
+#define BITMAP_BITS 256
+
+static void bit_flip(unsigned char bits[], unsigned int idx)
+{
+ bits[idx / CHAR_BIT] ^= (1 << (idx % CHAR_BIT));
+}
+
+/* We record offsets in a bitmap for the particular chain it should be in. */
+static void record_offset(unsigned char bits[], tdb_off_t off)
+{
+ uint32_t h1 = off, h2 = 0;
+ unsigned int i;
+
+ /* We get two good hash values out of jhash2, so we use both. Then
+ * we keep going to produce further hash values. */
+ for (i = 0; i < NUM_HASHES / 2; i++) {
+ hash(off, &h1, &h2);
+ bit_flip(bits, h1 % BITMAP_BITS);
+ bit_flip(bits, h2 % BITMAP_BITS);
+ h2++;
+ }
+}
+
+/* Check that an in-use record is valid. */
static bool tdb_check_used_record(struct tdb_context *tdb,
tdb_off_t off,
const struct list_struct *rec,
if (rec->key_len + rec->data_len + sizeof(tdb_off_t) > rec->rec_len)
return false;
- key = get_data(tdb, off + sizeof(*rec), rec->key_len);
+ key = get_bytes(tdb, off + sizeof(*rec), rec->key_len);
if (!key.dptr)
return false;
if (tdb->hash_fn(&key) != rec->full_hash)
goto fail_put_key;
- add_to_hash(hashes[BUCKET(rec->full_hash)+1], off);
+ /* Mark this offset as a known value for this hash bucket. */
+ record_offset(hashes[BUCKET(rec->full_hash)+1], off);
+ /* And similarly if the next pointer is valid. */
if (rec->next)
- add_to_hash(hashes[BUCKET(rec->full_hash)+1], rec->next);
+ record_offset(hashes[BUCKET(rec->full_hash)+1], rec->next);
- /* If they supply a check function, get data. */
- if (check) {
- data = get_data(tdb, off + sizeof(*rec) + rec->key_len,
- rec->data_len);
+ /* If they supply a check function and this record isn't dead,
+ get data and feed it. */
+ if (check && rec->magic != TDB_DEAD_MAGIC) {
+ data = get_bytes(tdb, off + sizeof(*rec) + rec->key_len,
+ rec->data_len);
if (!data.dptr)
goto fail_put_key;
if (check(key, data, private) == -1)
goto fail_put_data;
- put_data(tdb, data);
+ put_bytes(tdb, data);
}
- put_data(tdb, key);
+ put_bytes(tdb, key);
return true;
fail_put_data:
- put_data(tdb, data);
+ put_bytes(tdb, data);
fail_put_key:
- put_data(tdb, key);
+ put_bytes(tdb, key);
return false;
}
+/* Check that an unused record is valid. */
static bool tdb_check_free_record(struct tdb_context *tdb,
tdb_off_t off,
const struct list_struct *rec,
if (!tdb_check_record(tdb, off, rec))
return false;
- add_to_hash(hashes[0], off);
+ /* Mark this offset as a known value for the free list. */
+ record_offset(hashes[0], off);
+ /* And similarly if the next pointer is valid. */
if (rec->next)
- add_to_hash(hashes[0], rec->next);
+ record_offset(hashes[0], rec->next);
return true;
}
-/* We do this via linear scan, even though it's not 100% accurate. */
int tdb_check(struct tdb_context *tdb,
int (*check)(TDB_DATA key, TDB_DATA data, void *private),
void *private)
/* Make sure we know true size of the underlying file. */
tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);
+ /* Header must be OK: also gets us the recovery ptr, if any. */
if (!tdb_check_header(tdb, &recovery_start))
goto unlock;
+ /* We should have the whole header, too. */
if (tdb->map_size < TDB_DATA_START(tdb->header.hash_size)) {
tdb->ecode = TDB_ERR_CORRUPT;
goto unlock;
for (h = 1; h < 1+tdb->header.hash_size; h++)
hashes[h] = hashes[h-1] + BITMAP_BITS / CHAR_BIT;
- /* Freelist and hash headers are all in a row. */
+ /* Freelist and hash headers are all in a row: read them. */
for (h = 0; h < 1+tdb->header.hash_size; h++) {
if (tdb_ofs_read(tdb, FREELIST_TOP + h*sizeof(tdb_off_t),
&off) == -1)
goto free;
if (off)
- add_to_hash(hashes[h], off);
+ record_offset(hashes[h], off);
}
+ /* For each record, read it in and check it's ok. */
for (off = TDB_DATA_START(tdb->header.hash_size);
off < tdb->map_size;
off += sizeof(rec) + rec.rec_len) {
}
}
- /* We must have found recovery area. */
+ /* We must have found recovery area if there was one. */
if (recovery_start != 0 && !found_recovery)
goto free;
return 0;
}
-int main(int argc, char *argv[])
+static void tdb_flip_bit(struct tdb_context *tdb, unsigned int bit)
+{
+ unsigned int off = bit / CHAR_BIT;
+ unsigned char mask = (1 << (bit % CHAR_BIT));
+
+ if (tdb->map_ptr)
+ ((unsigned char *)tdb->map_ptr)[off] ^= mask;
+ else {
+ unsigned char c;
+ pread(tdb->fd, &c, 1, off);
+ c ^= mask;
+ pwrite(tdb->fd, &c, 1, off);
+ }
+}
+
+static void check_test(struct tdb_context *tdb)
{
- struct tdb_context *tdb;
TDB_DATA key, data;
unsigned int i, verifiable, corrupt, sizes[2], dsize, ksize;
- plan_tests(2);
- tdb = tdb_open("/tmp/test6.tdb", 2, TDB_CLEAR_IF_FIRST,
- O_CREAT|O_TRUNC|O_RDWR, 0600);
-
- if (!tdb)
- abort();
ok1(tdb_check(tdb, NULL, NULL) == 0);
key.dptr = (void *)"hello";
/* Flip one bit at a time, make sure it detects verifiable bytes. */
for (i = 0, corrupt = 0; i < tdb->map_size * CHAR_BIT; i++) {
- bit_flip(tdb->map_ptr, i);
+ tdb_flip_bit(tdb, i);
memset(sizes, 0, sizeof(sizes));
if (tdb_check(tdb, check, sizes) != 0)
corrupt++;
else if (sizes[0] != ksize || sizes[1] != dsize)
corrupt++;
- bit_flip(tdb->map_ptr, i);
+ tdb_flip_bit(tdb, i);
}
ok(corrupt == verifiable * CHAR_BIT, "corrupt %u should be %u",
corrupt, verifiable * CHAR_BIT);
+}
+
+int main(int argc, char *argv[])
+{
+ struct tdb_context *tdb;
+
+ plan_tests(4);
+ /* This should use mmap. */
+ tdb = tdb_open("/tmp/test6.tdb", 2, TDB_CLEAR_IF_FIRST,
+ O_CREAT|O_TRUNC|O_RDWR, 0600);
+
+ if (!tdb)
+ abort();
+ check_test(tdb);
+ tdb_close(tdb);
+
+ /* This should not. */
+ tdb = tdb_open("/tmp/test6.tdb", 2, TDB_CLEAR_IF_FIRST|TDB_NOMMAP,
+ O_CREAT|O_TRUNC|O_RDWR, 0600);
+
+ if (!tdb)
+ abort();
+ check_test(tdb);
tdb_close(tdb);
return exit_status();
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