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Reworked lookahead buffer (again) to avoid shifting bits

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The main reason for this change is to allow keeping track of existing
known-free blocks while trying to find more free blocks. This makes it
so failed filesystem traversals don't result in negative progress, which
is nice.

This was difficult in the previous lookahead scheme, since we we'd need
to shift the lookahead buffer to keep off=0 rooted at the first bit.
Shifting bytes is relatively easily with memmove, but it gets tricky
when shifting bits:

  lookahead before: ???? ???? ???? ??00 1101 0101 00?? ????
                                     ^              ^
                                    off          off+size

  shift:            0011 0101 0100 ???? ???? ???? ???? ????
                    ^              ^
                   off          off+size

  traverse:         0011 0101 0100 0000 0000 0000 1100 0000
                    ^                                       ^
                   off                                   off+size

Instead, we now just let the lookahead buffer wrap around. No shifting
required:

  lookahead before: ???? ???? ???? ??00 1101 0101 00?? ????
                                     ^              ^
                                    off          off+size

  traverse:         0000 0000 1100 0000 1101 0101 0000 0000
                                     ^
                                    off
                                     ^
                                  off+size

This gets a bit confusing with the lookahead window also wrapping around
disk, but the math works out with enough modulos (if modulos are too
expensive, we should eventually be able to optimize these into simple
bit masks via compile-time config).

In the future, if we move away from the const config struct, it would
also be nice to try to reducing the number of modulos by storing the
lookahead buffer size in bits instead of bytes...

Note that if the lookahead buffer is larger than disk, the lookahead
window will sort of travel around the underlying buffer. This isn't
inherently a problem, but it did cause some bugs.

To avoid similar bit-related problems with zeroing, lfs_alloc_inc now
also zeros bits as we allocate/skip them, so bits should always be zero
when we start a lookahead traversal. Though note we still need to
manually memset the buffer when discarding lookahead state in init/grow.

---

The end result is surprisingly a net savings in terms of code size. I
guess mainly due to dropping all the lfs_alloc_shift calls:

           code          stack
  before: 36472           2680
  after:  36412 (-0.2%)   2680 (+0.0%)
This commit is contained in:
Christopher Haster
2024-07-16 17:04:53 -05:00
parent 4fe46a983f
commit 4fc03f95a7
4 changed files with 179 additions and 182 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lfs.c
+71 -74
View File
@@ -5934,7 +5934,9 @@ static bool lfsr_fs_isinconsistent(const lfs_t *lfs) {
}
static bool lfsr_fs_canlookahead(const lfs_t *lfs) {
return lfs->lookahead.next > 0 || lfs->lookahead.size == 0;
return lfs->lookahead.size < lfs_min(
8*lfs->cfg->lookahead_size,
lfs->cfg->block_size);
}
@@ -8704,6 +8706,9 @@ static int lfsr_mtree_gc(lfs_t *lfs, lfsr_traversal_t *t,
// swap dirty/mutated flags while in lfsr_mtree_gc
t->o.o.flags = lfsr_f_swapdirty(t->o.o.flags);
// checkpoint the allocator to maximize any lookahead scans
lfs_alloc_ckpoint(lfs);
dropped:;
lfsr_tag_t tag;
lfsr_bptr_t bptr;
@@ -8907,43 +8912,33 @@ static void lfs_alloc_ckpoint(lfs_t *lfs) {
// discard any lookahead state, this is necessary if block_count changes
static void lfs_alloc_discard(lfs_t *lfs) {
// go ahead shift to next available block, we probably want the next
// scan to start here
lfs->lookahead.start = (lfs->lookahead.start + lfs->lookahead.next)
% lfs->block_count;
lfs->lookahead.next = 0;
lfs->lookahead.size = 0;
}
// shift the lookahead buffer to try to allocate more blocks, may do nothing
static void lfs_alloc_shift(lfs_t *lfs) {
// do nothing if shifting would make no progress
if (lfs->lookahead.next > 0) {
// discard already shifts to the next block
lfs_alloc_discard(lfs);
}
// zero lookahead buffer
if (lfs->lookahead.size == 0) {
lfs_memset(lfs->lookahead.buffer, 0, lfs->cfg->lookahead_size);
}
// don't update size until a successful lookahead scan
}
// mark a block as in-use
static void lfs_alloc_markinuse(lfs_t *lfs, lfs_block_t block) {
// translate to lookahead-relative
lfs_block_t mark = (block + lfs->block_count - lfs->lookahead.start)
% lfs->block_count;
if (mark < 8*lfs->cfg->lookahead_size) {
lfs_block_t block_ = ((
(lfs_sblock_t)(block
- (lfs->lookahead.window + lfs->lookahead.off))
// we only need this mess because C's mod is actually rem, and
// we want real mod in case block_ goes negative
% (lfs_sblock_t)lfs->block_count)
+ (lfs_sblock_t)lfs->block_count)
% (lfs_sblock_t)lfs->block_count;
if (block_ < 8*lfs->cfg->lookahead_size) {
// mark as in-use
lfs->lookahead.buffer[mark / 8] |= 1 << (mark % 8);
lfs->lookahead.buffer[
((lfs->lookahead.off + block_) / 8)
% lfs->cfg->lookahead_size]
|= 1 << ((lfs->lookahead.off + block_) % 8);
}
}
// needed in lfs_alloc_markfree
static lfs_sblock_t lfs_alloc_findnext(lfs_t *lfs);
static lfs_sblock_t lfs_alloc_findfree(lfs_t *lfs);
// mark any not-in-use blocks as free
static void lfs_alloc_markfree(lfs_t *lfs) {
@@ -8952,22 +8947,44 @@ static void lfs_alloc_markfree(lfs_t *lfs) {
8*lfs->cfg->lookahead_size,
lfs->lookahead.ckpoint);
// eagerly find the next free block so shift can make progress
lfs_alloc_findnext(lfs);
// eagerly find the next free block so lookahead scans can make
// the most progress
lfs_alloc_findfree(lfs);
}
// find next free block in lookahead buffer, if there is one
static lfs_sblock_t lfs_alloc_findnext(lfs_t *lfs) {
while (lfs->lookahead.next < lfs->lookahead.size) {
if (!(lfs->lookahead.buffer[lfs->lookahead.next / 8]
& (1 << (lfs->lookahead.next % 8)))) {
// found a free block
return (lfs->lookahead.start + lfs->lookahead.next)
// increment lookahead buffer
static void lfs_alloc_inc(lfs_t *lfs) {
LFS_ASSERT(lfs->lookahead.size > 0);
// clear lookahead as we increment
lfs->lookahead.buffer[lfs->lookahead.off / 8]
&= ~(1 << (lfs->lookahead.off % 8));
// increment next/off
lfs->lookahead.off += 1;
if (lfs->lookahead.off == 8*lfs->cfg->lookahead_size) {
lfs->lookahead.off = 0;
lfs->lookahead.window = (lfs->lookahead.window
+ 8*lfs->cfg->lookahead_size)
% lfs->block_count;
}
lfs->lookahead.next += 1;
// decrement size/ckpoint
lfs->lookahead.size -= 1;
lfs->lookahead.ckpoint -= 1;
}
// find next free block in lookahead buffer, if there is one
static lfs_sblock_t lfs_alloc_findfree(lfs_t *lfs) {
while (lfs->lookahead.size > 0) {
if (!(lfs->lookahead.buffer[lfs->lookahead.off / 8]
& (1 << (lfs->lookahead.off % 8)))) {
// found a free block
return (lfs->lookahead.window + lfs->lookahead.off)
% lfs->block_count;
}
lfs_alloc_inc(lfs);
}
return LFS_ERR_NOSPC;
@@ -8976,7 +8993,7 @@ static lfs_sblock_t lfs_alloc_findnext(lfs_t *lfs) {
static lfs_sblock_t lfs_alloc(lfs_t *lfs, bool erase) {
while (true) {
// scan our lookahead buffer for free blocks
lfs_sblock_t block = lfs_alloc_findnext(lfs);
lfs_sblock_t block = lfs_alloc_findfree(lfs);
if (block < 0 && block != LFS_ERR_NOSPC) {
return block;
}
@@ -8991,8 +9008,7 @@ static lfs_sblock_t lfs_alloc(lfs_t *lfs, bool erase) {
if (err) {
// bad erase? try another block
if (err == LFS_ERR_CORRUPT) {
lfs->lookahead.next += 1;
lfs->lookahead.ckpoint -= 1;
lfs_alloc_inc(lfs);
continue;
}
return err;
@@ -9001,33 +9017,31 @@ static lfs_sblock_t lfs_alloc(lfs_t *lfs, bool erase) {
// eagerly find the next free block to maximize how many blocks
// lfs_alloc_ckpoint makes available for scanning
lfs->lookahead.next += 1;
lfs->lookahead.ckpoint -= 1;
lfs_alloc_findnext(lfs);
lfs_alloc_inc(lfs);
lfs_alloc_findfree(lfs);
return block;
}
// In order to keep our block allocator from spinning forever when our
// in order to keep our block allocator from spinning forever when our
// filesystem is full, we mark points where there are no in-flight
// allocations with a checkpoint before starting a set of allocations.
// allocations with a checkpoint before starting a set of allocations
//
// If we've looked at all blocks since the last checkpoint, we report
// the filesystem as out of storage.
// if we've looked at all blocks since the last checkpoint, we report
// the filesystem as out of storage
//
if (lfs->lookahead.ckpoint <= 0) {
LFS_ERROR("No more free space 0x%"PRIx32,
(lfs->lookahead.start + lfs->lookahead.next)
LFS_ERROR("No more free space (0x%"PRIx32")",
(lfs->lookahead.window + lfs->lookahead.off)
% lfs->block_count);
return LFS_ERR_NOSPC;
}
// no blocks in our lookahead buffer, we need to scan the filesystem
// for unused blocks in the next lookahead window
lfs_alloc_shift(lfs);
// no blocks in our lookahead buffer?
//
// traverse the filesystem, building up knowledge of what blocks are
// in use in our lookahead window
// in use in the next lookahead window
//
lfsr_traversal_t t = LFSR_TRAVERSAL(LFS_T_LOOKAHEAD);
while (true) {
int err = lfsr_mtree_traverse(lfs, &t,
@@ -11901,10 +11915,11 @@ static int lfs_init(lfs_t *lfs, uint32_t flags,
goto failed;
}
}
lfs->lookahead.start = 0;
lfs->lookahead.window = 0;
lfs->lookahead.off = 0;
lfs->lookahead.size = 0;
lfs->lookahead.next = 0;
lfs->lookahead.ckpoint = 0;
lfs_alloc_discard(lfs);
// check that the size limits are sane
LFS_ASSERT(lfs->cfg->name_limit <= LFS_NAME_MAX);
@@ -12551,7 +12566,7 @@ static int lfsr_mountinited(lfs_t *lfs) {
// the purpose of this is to avoid bad wear patterns such as always
// allocating blocks near the beginning of disk after a power-loss
//
lfs->lookahead.start = lfs->seed % lfs->block_count;
lfs->lookahead.window = lfs->seed % lfs->block_count;
// TODO should the consumegdelta above take gstate/gdelta as a parameter?
// keep track of the current gstate on disk
@@ -12687,12 +12702,6 @@ int lfsr_mount(lfs_t *lfs, uint32_t flags,
lfsr_traversal_t t = LFSR_TRAVERSAL(flags_);
lfsr_omdir_open(lfs, &t.o.o);
// shift the lookahead buffer if requested
if (lfsr_t_islookahead(t.o.o.flags)) {
lfs_alloc_shift(lfs);
lfs_alloc_ckpoint(lfs);
}
while (true) {
err = lfsr_mtree_gc(lfs, &t,
NULL, NULL);
@@ -13133,12 +13142,6 @@ int lfsr_fs_gc(lfs_t *lfs, uint32_t flags) {
} else {
lfs->gc = LFSR_TRAVERSAL(flags);
lfsr_omdir_open(lfs, &lfs->gc.o.o);
// shift the lookahead buffer if requested
if (lfsr_t_islookahead(lfs->gc.o.o.flags)) {
lfs_alloc_shift(lfs);
lfs_alloc_ckpoint(lfs);
}
}
for (uint32_t i = 0;
@@ -13385,12 +13388,6 @@ static int lfsr_traversal_rewind_(lfs_t *lfs, lfsr_traversal_t *t) {
t->blocks[0] = -1;
t->blocks[1] = -1;
// shift the lookahead buffer if requested
if (lfsr_t_islookahead(t->o.o.flags)) {
lfs_alloc_shift(lfs);
lfs_alloc_ckpoint(lfs);
}
return 0;
}
lfs.h
+2 -2
View File
@@ -764,9 +764,9 @@ typedef struct lfs {
} pcache;
struct lfs_lookahead {
lfs_block_t start;
lfs_block_t window;
lfs_block_t off;
lfs_block_t size;
lfs_block_t next;
lfs_block_t ckpoint;
uint8_t *buffer;
} lookahead;
tests/test_badblocks.toml
+6 -6
View File
@@ -52,10 +52,10 @@ code = '''
CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -1787,10 +1787,10 @@ code = '''
CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -3522,10 +3522,10 @@ code = '''
CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
tests/test_btree.toml
+100 -100
View File
@@ -13,10 +13,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create an empty tree
@@ -44,10 +44,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -85,10 +85,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -134,10 +134,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -184,10 +184,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -242,10 +242,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -303,10 +303,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -353,10 +353,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -405,10 +405,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -487,10 +487,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -555,10 +555,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -690,10 +690,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -735,10 +735,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -793,10 +793,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -865,10 +865,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -922,10 +922,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -1008,10 +1008,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -1081,10 +1081,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -1224,10 +1224,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -1280,10 +1280,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -1352,10 +1352,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -1424,10 +1424,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -1515,10 +1515,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -1594,10 +1594,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -1676,10 +1676,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -1764,10 +1764,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -1870,10 +1870,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -2020,10 +2020,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -2079,10 +2079,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -2168,10 +2168,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -2228,10 +2228,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -2404,10 +2404,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree
@@ -2471,10 +2471,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree
@@ -2541,10 +2541,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree
@@ -2604,10 +2604,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree
@@ -2684,10 +2684,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -2790,10 +2790,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -2956,10 +2956,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a zero-entry tree
@@ -2989,10 +2989,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a single-entry tree
@@ -3041,10 +3041,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -3107,10 +3107,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -3187,10 +3187,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a two-entry tree
@@ -3268,10 +3268,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -3341,10 +3341,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -3455,10 +3455,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -3529,10 +3529,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -3685,10 +3685,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -3842,10 +3842,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree
@@ -4047,10 +4047,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a tree with N elements
@@ -4170,10 +4170,10 @@ code = '''
lfs_init(&lfs, LFS_M_RDWR, CFG) => 0;
// create free lookahead
memset(lfs.lookahead.buffer, 0, CFG->lookahead_size);
lfs.lookahead.start = 2;
lfs.lookahead.window = 2;
lfs.lookahead.off = 0;
lfs.lookahead.size = lfs_min(8*CFG->lookahead_size,
CFG->block_count-2);
lfs.lookahead.next = 2;
lfs_alloc_ckpoint(&lfs);
// create a btree