/**
* Make sure vector of block numbers is ordered and points to allocated data,
* but was not already flagged as being used by another key / value.
*
* @param what string describing what is being tested (key or value)
* @param db the sdbm database
* @param bvec vector where allocated block numbers are stored
* @param bcnt amount of blocks in vector
*
* @return TRUE on success.
*/
static gboolean
big_file_check(const char *what, DBM *db, const void *bvec, int bcnt)
{
size_t prev_bno = 0; /* 0 is invalid: it's the first bitmap */
const void *q;
int n;
if (!big_check_start(db))
return TRUE; /* Cannot validate, assume it's OK */
for (q = bvec, n = bcnt; n > 0; n--) {
size_t bno = peek_be32(q);
bit_field_t *map;
long bmap;
size_t bit;
if (!big_block_is_allocated(db, bno)) {
g_warning("sdbm: \"%s\": "
"%s from .pag refers to unallocated block %lu in .dat",
sdbm_name(db), what, (unsigned long) bno);
return FALSE;
}
if (prev_bno != 0 && bno <= prev_bno) {
g_warning("sdbm: \"%s\": "
"%s from .pag lists unordered block list (corrupted file?)",
sdbm_name(db), what);
return FALSE;
}
q = const_ptr_add_offset(q, sizeof(guint32));
prev_bno = bno;
/*
* Make sure block is not used by someone else.
*
* Because we mark blocks as used in big keys and values only after
* we validated both the key and the value for a given pair, we cannot
* detect shared blocks between the key and value of a pair.
*/
bmap = bno / BIG_BITCOUNT; /* Bitmap handling this block */
bit = bno & (BIG_BITCOUNT - 1); /* Index within bitmap */
g_assert(bmap < db->big->bitmaps);
map = ptr_add_offset(db->big->bitcheck, bmap * BIG_BLKSIZE);
if (bit_field_get(map, bit)) {
g_warning("sdbm: \"%s\": "
"%s from .pag refers to already seen block %lu in .dat",
sdbm_name(db), what, (unsigned long) bno);
return FALSE;
}
}
return TRUE;
}
/**
* Read n-th bitmap page.
*
* @return TRUE on success.
*/
static gboolean
fetch_bitbuf(DBM *db, long num)
{
DBMBIG *dbg = db->big;
long bno = num * BIG_BITCOUNT; /* address of n-th bitmap in file */
dbg->bitfetch++;
if (bno != dbg->bitbno) {
ssize_t got;
if (dbg->bitbuf_dirty && !flush_bitbuf(db))
return FALSE;
dbg->bitread++;
got = compat_pread(dbg->fd, dbg->bitbuf, BIG_BLKSIZE, OFF_DAT(bno));
if (got < 0) {
g_warning("sdbm: \"%s\": could not read bitmap block #%ld: %s",
sdbm_name(db), num, g_strerror(errno));
ioerr(db, FALSE);
return FALSE;
}
if (0 == got) {
memset(dbg->bitbuf, 0, BIG_BLKSIZE);
}
dbg->bitbno = bno;
dbg->bitbuf_dirty = FALSE;
} else {
dbg->bitbno_hit++;
}
return TRUE;
}
static void
log_lrustats(DBM *db)
{
struct lru_cache *cache = db->cache;
unsigned long raccesses = cache->rhits + cache->rmisses;
unsigned long waccesses = cache->whits + cache->wmisses;
g_info("sdbm: \"%s\" LRU cache size = %ld page%s, %s writes, %s DB",
sdbm_name(db), cache->pages, 1 == cache->pages ? "" : "s",
cache->write_deferred ? "deferred" : "synchronous",
db->is_volatile ? "volatile" : "persistent");
g_info("sdbm: \"%s\" LRU read cache hits = %.2f%% on %lu request%s",
sdbm_name(db), cache->rhits * 100.0 / MAX(raccesses, 1), raccesses,
1 == raccesses ? "" : "s");
g_info("sdbm: \"%s\" LRU write cache hits = %.2f%% on %lu request%s",
sdbm_name(db), cache->whits * 100.0 / MAX(waccesses, 1), waccesses,
1 == waccesses ? "" : "s");
}
static void
log_bigstats(DBM *db)
{
DBMBIG *dbg = db->big;
if (-1 == dbg->fd)
return; /* The .dat file was never used */
g_info("sdbm: \"%s\" bitmap reads = %lu, bitmap writes = %lu "
"(deferred %lu)",
sdbm_name(db), dbg->bitread, dbg->bitwrite, dbg->bitwdelayed);
g_info("sdbm: \"%s\" bitmap blocknum hits = %.2f%% on %lu request%s",
sdbm_name(db), dbg->bitbno_hit * 100.0 / MAX(dbg->bitfetch, 1),
dbg->bitfetch, 1 == dbg->bitfetch ? "" : "s");
g_info("sdbm: \"%s\" large key short matches = %.2f%% on %lu attempt%s",
sdbm_name(db),
dbg->key_short_match * 100.0 / MAX(dbg->key_matching, 1),
dbg->key_matching, 1 == dbg->key_matching ? "" : "s");
g_info("sdbm: \"%s\" large key full matches = %.2f%% on %lu attempt%s",
sdbm_name(db),
dbg->key_full_match * 100.0 / MAX(dbg->key_short_match, 1),
dbg->key_short_match, 1 == dbg->key_short_match ? "" : "s");
g_info("sdbm: \"%s\" big blocks read = %lu (%lu system call%s)",
sdbm_name(db),
dbg->bigread_blk, dbg->bigread, 1 == dbg->bigread ? "" : "s");
g_info("sdbm: \"%s\" big blocks written = %lu (%lu system call%s)",
sdbm_name(db),
dbg->bigwrite_blk, dbg->bigwrite, 1 == dbg->bigwrite ? "" : "s");
}
/**
* Mark .dat blocks used to hold the value described in the .pag space as
* being allocated in the bitmap checking array.
*
* @param db the sdbm database
* @param bval start of big value in the page
* @param blen length of big value in the page
*/
void
bigval_mark_used(DBM *db, const char *bval, size_t blen)
{
size_t len = big_length(bval);
if (bigval_length(len) != blen) {
g_carp("sdbm: \"%s\": %s: inconsistent value length %lu in .pag",
sdbm_name(db), G_STRFUNC, (unsigned long) len);
return;
}
big_file_mark_used(db, bigval_blocks(bval), bigblocks(len));
}
/**
* Shrink .dat file on disk to remove needlessly allocated blocks.
*
* @return TRUE if we were able to successfully shrink the file.
*/
gboolean
big_shrink(DBM *db)
{
DBMBIG *dbg = db->big;
long i;
filesize_t offset = 0;
if (-1 == dbg->fd) {
/*
* We do not want to call big_open() unless the .dat file already
* exists because that would create it and it was not needed so far.
*/
if (-1 == big_open_lazy(dbg, TRUE))
return 0 == errno;
}
g_assert(dbg->fd != -1);
/*
* Loop through all the currently existing bitmaps, starting from the last
* one, looking for the last set bit indicating the last used page.
*/
for (i = dbg->bitmaps - 1; i >= 0; i--) {
size_t bno;
if (!fetch_bitbuf(db, i))
return FALSE;
bno = bit_field_last_set(dbg->bitbuf, 0, BIG_BITCOUNT - 1);
if ((size_t) -1 == bno) {
g_warning("sdbm: \"%s\": corrupted bitmap #%ld, considered empty",
sdbm_name(db), i);
} else if (bno != 0) {
bno = size_saturate_add(bno, size_saturate_mult(BIG_BITCOUNT, i));
offset = OFF_DAT(bno + 1);
break;
}
}
if (-1 == ftruncate(dbg->fd, offset))
return FALSE;
dbg->bitmaps = i + 1; /* Possibly reduced the amount of bitmaps */
return TRUE;
}
/**
* Flush page to disk.
* @return TRUE on success
*/
gboolean
flushpag(DBM *db, char *pag, long num)
{
ssize_t w;
g_assert(num >= 0);
db->pagwrite++;
w = compat_pwrite(db->pagf, pag, DBM_PBLKSIZ, OFF_PAG(num));
if (w < 0 || w != DBM_PBLKSIZ) {
if (w < 0)
g_warning("sdbm: \"%s\": cannot flush page #%ld: %s",
sdbm_name(db), num, g_strerror(errno));
else
g_warning("sdbm: \"%s\": could only flush %u bytes from page #%ld",
sdbm_name(db), (unsigned) w, num);
ioerr(db, TRUE);
db->flush_errors++;
return FALSE;
}
return TRUE;
}
/**
* Validate .dat blocks used to hold the value described in the .pag space.
*
* @param db the sdbm database
* @param bval start of big value in the page
* @param blen length of big value in the page
*
* @return TRUE on success.
*/
gboolean
bigval_check(DBM *db, const char *bval, size_t blen)
{
size_t len = big_length(bval);
if (bigval_length(len) != blen) {
g_warning("sdbm: \"%s\": found inconsistent value length %lu, "
"would span %lu bytes in .pag instead of the %lu present",
sdbm_name(db), (unsigned long) len,
(unsigned long) bigkey_length(len), (unsigned long) blen);
return FALSE;
}
return big_file_check("value", db, bigval_blocks(bval), bigblocks(len));
}
/**
* Free .dat blocks used to hold the value described in the .pag space.
*
* @param db the sdbm database
* @param bval start of big value in the page
* @param blen length of big value in the page
*
* @return TRUE on success.
*/
gboolean
bigval_free(DBM *db, const char *bval, size_t blen)
{
size_t len = big_length(bval);
if (bigval_length(len) != blen) {
g_warning("sdbm: \"%s\": "
"bigval_free: inconsistent key length %lu in .pag",
sdbm_name(db), (unsigned long) len);
return FALSE;
}
big_file_free(db, bigval_blocks(bval), bigblocks(len));
return TRUE;
}
/**
* Get value data from the block numbers held in the .pag value.
*
* @param db the sdbm database
* @param bval start of big value in the page
* @param blen length of big value in the page
*
* @return pointer to read value (scratch buffer) if OK, NULL on error.
*/
char *
bigval_get(DBM *db, const char *bval, size_t blen)
{
size_t len = big_length(bval);
DBMBIG *dbg = db->big;
if (bigval_length(len) != blen) {
g_warning("sdbm: \"%s\": "
"bigval_get: inconsistent value length %lu in .pag",
sdbm_name(db), (unsigned long) len);
return NULL;
}
if (-1 == big_fetch(db, bigval_blocks(bval), len))
return NULL;
return dbg->scratch;
}
/**
* End bitmap allocation checks that have been started by the usage of one
* of the bigkey_mark_used() and bigval_mark_used() routines.
*
* @return the amount of corrections brought to the bitmap, 0 meaning
* everything was consistent.
*/
size_t
big_check_end(DBM *db)
{
DBMBIG *dbg = db->big;
long i;
size_t adjustments = 0;
if (NULL == dbg->bitcheck)
return 0;
for (i = 0; i < dbg->bitmaps; i++) {
if (!fetch_bitbuf(db, i)) {
adjustments += BIG_BITCOUNT; /* Say, everything was wrong */
} else {
guint8 *p = ptr_add_offset(dbg->bitcheck, i * BIG_BLKSIZE);
guint8 *q = dbg->bitbuf;
size_t j;
size_t old_adjustments = adjustments;
for (j = 0; j < BIG_BLKSIZE; j++, p++, q++) {
guint8 mismatch = *p ^ *q;
if (mismatch) {
adjustments += bits_set(mismatch);
*q = *p;
}
}
if (old_adjustments != adjustments) {
size_t adj = adjustments - old_adjustments;
flush_bitbuf(db);
g_warning("sdbm: \"%s\": adjusted %lu bit%s in bitmap #%ld",
sdbm_name(db), (unsigned long) adj, 1 == adj ? "" : "s", i);
}
}
}
HFREE_NULL(dbg->bitcheck);
return adjustments;
}
/**
* Flush bitmap to disk.
* @return TRUE on sucess
*/
static gboolean
flush_bitbuf(DBM *db)
{
DBMBIG *dbg = db->big;
ssize_t w;
dbg->bitwrite++;
w = compat_pwrite(dbg->fd, dbg->bitbuf, BIG_BLKSIZE, OFF_DAT(dbg->bitbno));
if (BIG_BLKSIZE == w) {
dbg->bitbuf_dirty = FALSE;
return TRUE;
}
g_warning("sdbm: \"%s\": cannot flush bitmap #%ld: %s",
sdbm_name(db), dbg->bitbno / BIG_BITCOUNT,
-1 == w ? g_strerror(errno) : "partial write");
ioerr(db, TRUE);
return FALSE;
}
/**
* Set the page cache size.
* @return 0 if OK, -1 on failure with errno set.
*/
int
setcache(DBM *db, long pages)
{
struct lru_cache *cache = db->cache;
bool wdelay;
sdbm_lru_check(cache);
if (pages <= 0) {
errno = EINVAL;
return -1;
}
if (NULL == cache)
return init_cache(db, pages, FALSE);
/*
* Easiest case: the size identical.
*/
if (pages == cache->pages)
return 0;
/*
* Cache size is changed.
*
* This means the arena will be reallocated, so we must invalidate the
* current db->pagbuf pointer, which lies within the old arena. It is
* sufficient to reset db->pagbno, forcing a reload from the upper layers.
* Note than when the cache size is enlarged, the old page is still cached
* so reloading will be just a matter of recomputing db->pagbuf. We could
* do so here, but cache size changes should only be infrequent.
*
* We also reset all the cache statistics, since a different cache size
* will imply a different set of hit/miss ratio.
*/
db->pagbno = -1; /* Current page address will become invalid */
db->pagbuf = NULL;
if (common_stats) {
s_info("sdbm: \"%s\" LRU cache size %s from %ld page%s to %ld",
sdbm_name(db), pages > cache->pages ? "increased" : "decreased",
cache->pages, plural(cache->pages), pages);
log_lrustats(db);
}
cache->rhits = cache->rmisses = 0;
cache->whits = cache->wmisses = 0;
/*
* Straightforward: the size is increased.
*/
if (pages > cache->pages) {
char *new_arena = vmm_alloc(pages * DBM_PBLKSIZ);
if (NULL == new_arena)
return -1;
memmove(new_arena, cache->arena, cache->pages * DBM_PBLKSIZ);
vmm_free(cache->arena, cache->pages * DBM_PBLKSIZ);
cache->arena = new_arena;
cache->dirty = wrealloc(cache->dirty, cache->pages, pages);
cache->numpag = wrealloc(cache->numpag,
cache->pages * sizeof(long), pages * sizeof(long));
cache->pages = pages;
return 0;
}
/*
* Difficult: the size is decreased.
*
* The current page buffer could point in a cache area that is going
* to disappear, and the internal data structures must forget about
* all the old indices that are greater than the new limit.
*
* We do not try to optimize anything here, as this call should happen
* only infrequently: we flush the current cache (in case there are
* deferred writes), destroy the LRU cache data structures, recreate a
* new one and invalidate the current DB page.
*/
wdelay = cache->write_deferred;
flush_dirtypag(db);
free_cache(cache);
return setup_cache(cache, pages, wdelay);
}
/**
* Store big value in the .dat file, writing to the supplied block numbers.
*
* @param db the sdbm database
* @param bvec start of block vector, containing block numbers
* @param data start of data to write
* @param len length of data to write
*
* @return -1 on error with errno set, 0 if OK.
*/
static int
big_store(DBM *db, const void *bvec, const void *data, size_t len)
{
DBMBIG *dbg = db->big;
int bcnt = bigbcnt(len);
int n;
const void *p;
const char *q;
size_t remain;
g_return_val_if_fail(NULL == dbg->bitcheck, -1);
if (-1 == dbg->fd && -1 == big_open(dbg))
return -1;
/*
* Look at the amount of consecutive block numbers we have to be able
* to write into them via a single system call.
*/
n = bcnt;
p = bvec;
q = data;
remain = len;
while (n > 0) {
size_t towrite = MIN(remain, BIG_BLKSIZE);
guint32 bno = peek_be32(p);
guint32 prev_bno = bno;
p = const_ptr_add_offset(p, sizeof(guint32));
n--;
remain = size_saturate_sub(remain, towrite);
while (n > 0) {
guint32 next_bno = peek_be32(p);
size_t amount;
if (next_bno <= prev_bno) /* Block numbers are sorted */
goto corrupted_page;
if (next_bno - prev_bno != 1)
break; /* Not consecutive */
prev_bno = next_bno;
p = const_ptr_add_offset(p, sizeof(guint32));
amount = MIN(remain, BIG_BLKSIZE);
towrite += amount;
n--;
remain = size_saturate_sub(remain, amount);
}
dbg->bigwrite++;
if (-1 == compat_pwrite(dbg->fd, q, towrite, OFF_DAT(bno))) {
g_warning("sdbm: \"%s\": "
"could not write %lu bytes starting at data block #%u: %s",
sdbm_name(db), (unsigned long) towrite, bno, g_strerror(errno));
ioerr(db, TRUE);
return -1;
}
q += towrite;
dbg->bigwrite_blk += bigblocks(towrite);
g_assert(ptr_diff(q, data) <= len);
}
g_assert(ptr_diff(q, data) == len);
return 0;
corrupted_page:
g_warning("sdbm: \"%s\": corrupted page: %d big data block%s not sorted",
sdbm_name(db), bcnt, 1 == bcnt ? "" : "s");
ioerr(db, FALSE);
errno = EFAULT; /* Data corrupted somehow (.pag file) */
return -1;
}
/**
* Is a big key stored at bkey in an SDBM .pag file equal to a siz-byte key?
*
* @param db the sdbm database
* @param bkey start of big key in the page
* @param blen length of big key in the page
* @param key the key we're trying to match against
* @param siz length of the key
*
* @return TRUE if the key matches.
*/
gboolean
bigkey_eq(DBM *db, const char *bkey, size_t blen, const char *key, size_t siz)
{
size_t len = big_length(bkey);
DBMBIG *dbg = db->big;
g_assert(bigkey_length(len) == blen);
/*
* Comparing a key in memory with a big key on disk is potentially a
* costly operation because it requires some I/O to fetch the key from
* the .dat file, which may involve several system calls, simply to find
* out that the key is not matching.
*
* To avoid useless reads as much as possible, we store the length of
* the big key at the beginning of the .pag key indirection data. If the
* size does not match, there's no need to go further.
*
* Then we keep the first and last BIG_KEYSAVED bytes of the key as part
* of the .pag data so that we may quickly filter out keys that are
* obviously not matching.
*
* Only when things look like it could be a match do we engage in the
* process of fetching the big key data to perform the actual comparison.
*
* Nonetheless this means fetching data indexed by large keys requires
* extra I/Os and therefore large keys should be avoided if possible.
* In practice, keys are shorthand to the actual data and therefore are
* likely to be kept short enough so that they are always expanded in the
* .pag data and never stored as big keys.
*/
if (siz != len)
return FALSE;
dbg->key_matching++;
if (0 != memcmp(key, bigkey_head(bkey), BIG_KEYSAVED))
return FALSE;
if (0 != memcmp(key + (siz-BIG_KEYSAVED), bigkey_tail(bkey), BIG_KEYSAVED))
return FALSE;
dbg->key_short_match++;
/*
* Need to read the key to make sure it's an exact match.
*
* There is a high probability as the head and the tail already match,
* and the length is the same.
*/
if (-1 == big_fetch(db, bigkey_blocks(bkey), siz))
return FALSE;
/*
* Data stored in the .dat file must match what the .pag had for the key
*/
if (
0 != memcmp(db->big->scratch, bigkey_head(bkey), BIG_KEYSAVED) ||
0 != memcmp(db->big->scratch + (siz-BIG_KEYSAVED),
bigkey_tail(bkey), BIG_KEYSAVED)
) {
g_warning("sdbm: \"%s\": found %lu-byte key page/data inconsistency",
sdbm_name(db), (unsigned long) siz);
return FALSE;
}
if (0 == memcmp(db->big->scratch, key, siz)) {
dbg->key_full_match++;
return TRUE;
}
return FALSE;
}
/**
* Fetch data block from the .dat file, reading from the supplied block numbers.
*
* @param db the sdbm database
* @param bvec start of block vector, containing block numbers
* @param len length of the data to be read
*
* @return -1 on error with errno set, 0 if OK. Read data is left in the
* scratch buffer.
*/
static int
big_fetch(DBM *db, const void *bvec, size_t len)
{
int bcnt = bigbcnt(len);
DBMBIG *dbg = db->big;
int n;
const void *p;
char *q;
size_t remain;
guint32 prev_bno;
if (-1 == dbg->fd && -1 == big_open(dbg))
return -1;
if (dbg->scratch_len < len)
big_scratch_grow(dbg, len);
/*
* Read consecutive blocks in one single system call.
*/
n = bcnt;
p = bvec;
q = dbg->scratch;
remain = len;
while (n > 0) {
size_t toread = MIN(remain, BIG_BLKSIZE);
guint32 bno = peek_be32(p);
prev_bno = bno;
if (!big_block_is_allocated(db, prev_bno))
goto corrupted_database;
p = const_ptr_add_offset(p, sizeof(guint32));
n--;
remain = size_saturate_sub(remain, toread);
while (n > 0) {
guint32 next_bno = peek_be32(p);
size_t amount;
if (next_bno <= prev_bno) /* Block numbers are sorted */
goto corrupted_page;
if (next_bno - prev_bno != 1)
break; /* Not consecutive */
prev_bno = next_bno;
if (!big_block_is_allocated(db, prev_bno))
goto corrupted_database;
p = const_ptr_add_offset(p, sizeof(guint32));
amount = MIN(remain, BIG_BLKSIZE);
toread += amount;
n--;
remain = size_saturate_sub(remain, amount);
}
dbg->bigread++;
if (-1 == compat_pread(dbg->fd, q, toread, OFF_DAT(bno))) {
g_warning("sdbm: \"%s\": "
"could not read %lu bytes starting at data block #%u: %s",
sdbm_name(db), (unsigned long) toread, bno, g_strerror(errno));
ioerr(db, FALSE);
return -1;
}
q += toread;
dbg->bigread_blk += bigblocks(toread);
g_assert(UNSIGNED(q - dbg->scratch) <= dbg->scratch_len);
}
g_assert(UNSIGNED(q - dbg->scratch) == len);
return 0;
corrupted_database:
g_warning("sdbm: \"%s\": cannot read unallocated data block #%u",
sdbm_name(db), prev_bno);
goto fault;
corrupted_page:
g_warning("sdbm: \"%s\": corrupted page: %d big data block%s not sorted",
sdbm_name(db), bcnt, 1 == bcnt ? "" : "s");
/* FALL THROUGH */
fault:
ioerr(db, FALSE);
errno = EFAULT; /* Data corrupted somehow (.pag or .dat file) */
return -1;
}
/**
* Free a block from file.
*/
static void
big_ffree(DBM *db, size_t bno)
{
DBMBIG *dbg = db->big;
long bmap;
size_t i;
STATIC_ASSERT(IS_POWER_OF_2(BIG_BITCOUNT));
if (-1 == dbg->fd && -1 == big_open(dbg)) {
g_warning("sdbm: \"%s\": cannot free block #%ld",
sdbm_name(db), (long) bno);
return;
}
/*
* Block number must be positive, and we cannot free a bitmap block.
* If we end-up doing it, then it means data in the .pag was corrupted,
* so we do not assert but fail gracefully.
*/
if (!size_is_positive(bno) || 0 == (bno & (BIG_BITCOUNT - 1))) {
g_warning("sdbm: \"%s\": attempt to free invalid block #%ld",
sdbm_name(db), (long) bno);
return;
}
g_assert(size_is_positive(bno)); /* Can never free block 0 (bitmap!) */
g_assert(bno & (BIG_BITCOUNT - 1)); /* Cannot be a bitmap block */
bmap = bno / BIG_BITCOUNT; /* Bitmap handling this block */
i = bno & (BIG_BITCOUNT - 1); /* Index within bitmap */
/*
* Likewise, if the block falls in a bitmap we do not know about yet,
* the .pag was corrupted.
*/
if (bmap >= dbg->bitmaps) {
g_warning("sdbm: \"%s\": "
"freed block #%ld falls within invalid bitmap #%ld (max %ld)",
sdbm_name(db), (long) bno, bmap, dbg->bitmaps - 1);
return;
}
if (!fetch_bitbuf(db, bmap))
return;
/*
* Again, freeing a block that is already marked as being freed is
* a severe error but can happen if the bitmap cannot be flushed to disk
* at some point, hence it cannot be an assertion.
*/
if (!bit_field_get(dbg->bitbuf, i)) {
g_warning("sdbm: \"%s\": freed block #%ld was already marked as free",
sdbm_name(db), (long) bno);
return;
}
bit_field_clear(dbg->bitbuf, i);
dbg->bitbuf_dirty = TRUE;
}
/**
* Get a new index in the cache, and update LRU data structures.
*
* @param db the database
* @param num page number in the DB for which we want a cache index
*
*
* @return -1 on error, or the allocated cache index.
*/
static int
getidx(DBM *db, long num)
{
struct lru_cache *cache = db->cache;
long n; /* Cache index */
/*
* If we invalidated pages, reuse their indices.
* If we have not used all the pages yet, get the next one.
* Otherwise, use the least-recently requested page.
*/
if (slist_length(cache->available)) {
void *v = slist_shift(cache->available);
n = pointer_to_int(v);
g_assert(n >= 0 && n < cache->pages);
g_assert(!cache->dirty[n]);
g_assert(-1 == cache->numpag[n]);
hash_list_prepend(cache->used, int_to_pointer(n));
} else if (cache->next < cache->pages) {
n = cache->next++;
cache->dirty[n] = FALSE;
hash_list_prepend(cache->used, int_to_pointer(n));
} else {
void *last = hash_list_tail(cache->used);
long oldnum;
gboolean had_ioerr = booleanize(db->flags & DBM_IOERR_W);
hash_list_moveto_head(cache->used, last);
n = pointer_to_int(last);
/*
* This page is no longer cached as its cache index is being reused
* Flush it to disk if dirty before discarding it.
*/
g_assert(n >= 0 && n < cache->pages);
oldnum = cache->numpag[n];
if (cache->dirty[n] && !writebuf(db, oldnum, n)) {
hash_list_iter_t *iter;
void *item;
gboolean found = FALSE;
/*
* Cannot flush dirty page now, probably because we ran out of
* disk space. Look through the cache whether we can reuse a
* non-dirty page instead, which would let us keep the dirty
* page a little longer in the cache, in the hope it can then
* be properly flushed later.
*/
iter = hash_list_iterator_tail(cache->used);
while (NULL != (item = hash_list_iter_previous(iter))) {
long i = pointer_to_int(item);
g_assert(i >= 0 && i < cache->pages);
if (!cache->dirty[i]) {
found = TRUE; /* OK, reuse cache slot #i then */
n = i;
oldnum = cache->numpag[i];
break;
}
}
hash_list_iter_release(&iter);
if (found) {
g_assert(item != NULL);
hash_list_moveto_head(cache->used, item);
/*
* Clear error condition if we had none prior to the flush
* attempt, since we can do without it for now.
*/
if (!had_ioerr)
db->flags &= ~DBM_IOERR_W;
g_warning("sdbm: \"%s\": "
"reusing cache slot used by clean page #%ld instead",
sdbm_name(db), oldnum);
} else {
g_warning("sdbm: \"%s\": cannot discard dirty page #%ld",
sdbm_name(db), oldnum);
return -1;
}
}
g_hash_table_remove(cache->pagnum, ulong_to_pointer(oldnum));
cache->dirty[n] = FALSE;
}
/*
* Record the association between the cache index and the page number.
*/
g_assert(n >= 0 && n < cache->pages);
cache->numpag[n] = num;
g_hash_table_insert(cache->pagnum,
ulong_to_pointer(num), int_to_pointer(n));
return n;
}