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littlefs/lfs_util.h
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Christopher Haster 9ac73ceb86 Reverted non-dag file bshrubs/btrees 
Ok so, funny story, looks like we won't actually need pure-tree
bshrubs/btrees.

It _is_ true that the single-parent constraint imposed by pure-trees can
enable a wider range of algorithms. But looking forward into the planned
design, we just happen to not need this constraint at all. I made a
mistake here:

1. Block allocation - On paper block allocation benefits the most from
   the single-parent constraint. But we have another daggish problem,
   how do we efficiently account for in-flight/open btrees?

   Naively, you might think we can just traverse all open btrees during
   allocation, since we shouldn't have _that_ many. But this scales
   O(n^2) when writing a large file. The key observation being that open
   files reference on-disk btrees and are _not_ RAM constrained.

   The current solution involves tree-diffing in order to figure out
   bmap updates. Which, humorously, works perfectly fine even if the
   trees are dags.

2. Error correction - I just completely forgot that the current plans
   for block redundancy require the ddtree.

   Each block gets mapped into the dense ddtree, with subranges of the
   ddtree grouped into parity groups backed by the ptree. Instead of
   bptrs, file btrees store indirect ddkeys into the ddtree. No bptrs?
   No dag problem!

   This is still a problem if we ever support naive data redund (redund
   blocks in a bptrs), but that's out of scope for other reasons
   (basically just a lot more code).

So reverting. Allowing dags allows for much faster random writes, at
least in theory.

---

For now I'm still keeping the dag-avoidance in lfsr_file_flush_ around
under the LFS_NONDAG ifdef. This will likely be dropped at some point,
but I'm curious how it affects benchmarks.

Ugh, and of course the unused label makes GCC unhappy. Added
-Wno-unused-label to CFLAGS because labels have other uses besides just
being goto targets (debug targets, code organization, etc).

We probably use labels more that other libraries because to littlefs's
no-recursion requirement.

Code changes minimal, still not sure where that stack difference comes
from:

           code          stack          ctx
  before: 35740           2424          640
  after:  35736 (-0.0%)   2440 (+0.7%)  640 (+0.0%)
2025-04-27 13:37:17 -05:00

782 lines
18 KiB
C
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/*
* lfs utility functions
*
* Copyright (c) 2022, The littlefs authors.
* Copyright (c) 2017, Arm Limited. All rights reserved.
* SPDX-License-Identifier: BSD-3-Clause
*/
#ifndef LFS_UTIL_H
#define LFS_UTIL_H
// Users can override lfs_util.h with their own configuration by defining
// LFS_CONFIG as a header file to include (-DLFS_CONFIG=lfs_config.h).
//
// If LFS_CONFIG is used, none of the default utils will be emitted and must be
// provided by the config file. To start, I would suggest copying lfs_util.h
// and modifying as needed.
#ifdef LFS_CONFIG
#define LFS_STRINGIZE(x) LFS_STRINGIZE2(x)
#define LFS_STRINGIZE2(x) #x
#include LFS_STRINGIZE(LFS_CONFIG)
#else
// Some convenient macro aliases
// TODO move these to something like lfs_cfg.h?
// LFS_BIGGEST enables all opt-in features
#ifdef LFS_BIGGEST
#ifndef LFS_REVDBG
#define LFS_REVDBG
#endif
#ifndef LFS_REVNOISE
#define LFS_REVNOISE
#endif
#ifndef LFS_CKPROGS
#define LFS_CKPROGS
#endif
#ifndef LFS_CKFETCHES
#define LFS_CKFETCHES
#endif
#ifndef LFS_CKPARITY
#define LFS_CKPARITY
#endif
#ifndef LFS_CKDATACKSUMS
#define LFS_CKDATACKSUMS
#endif
#ifndef LFS_GC
#define LFS_GC
#endif
#endif
// LFS_YES_* variants imply the relevant LFS_* macro
#ifdef LFS_YES_RDONLY
#define LFS_RDONLY
#endif
#ifdef LFS_YES_REVDBG
#define LFS_REVDBG
#endif
#ifdef LFS_YES_REVNOISE
#define LFS_REVNOISE
#endif
#ifdef LFS_YES_CKPROGS
#define LFS_CKPROGS
#endif
#ifdef LFS_YES_CKFETCHES
#define LFS_CKFETCHES
#endif
#ifdef LFS_YES_CKPARITY
#define LFS_CKPARITY
#endif
#ifdef LFS_YES_CKDATACKSUMS
#define LFS_CKDATACKSUMS
#endif
#ifdef LFS_YES_CKDATACKSUMS
#define LFS_CKDATACKSUMS
#endif
// LFS_NO_LOG disables all logging macros
#ifdef LFS_NO_LOG
#ifndef LFS_NO_DEBUG
#define LFS_NO_DEBUG
#endif
#ifndef LFS_NO_INFO
#define LFS_NO_INFO
#endif
#ifndef LFS_NO_WARN
#define LFS_NO_WARN
#endif
#ifndef LFS_NO_ERROR
#define LFS_NO_ERROR
#endif
#endif
// System includes
#include <stdint.h>
#include <stdbool.h>
#include <sys/types.h>
#include <inttypes.h>
#ifndef LFS_NO_STRINGH
#include <string.h>
#endif
#ifndef LFS_NO_MALLOC
#include <stdlib.h>
#endif
#ifndef LFS_NO_ASSERT
#include <assert.h>
#endif
#if !defined(LFS_NO_DEBUG) || \
!defined(LFS_NO_INFO) || \
!defined(LFS_NO_WARN) || \
!defined(LFS_NO_ERROR) || \
defined(LFS_YES_TRACE)
#include <stdio.h>
#endif
// Macros, may be replaced by system specific wrappers. Arguments to these
// macros must not have side-effects as the macros can be removed for a smaller
// code footprint
// Logging functions
#ifndef LFS_TRACE
#ifdef LFS_YES_TRACE
#define LFS_TRACE_(fmt, ...) \
printf("%s:%d:trace: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
#define LFS_TRACE(...) LFS_TRACE_(__VA_ARGS__, "")
#else
#define LFS_TRACE(...)
#endif
#endif
#ifndef LFS_DEBUG
#ifndef LFS_NO_DEBUG
#define LFS_DEBUG_(fmt, ...) \
printf("%s:%d:debug: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
#define LFS_DEBUG(...) LFS_DEBUG_(__VA_ARGS__, "")
#else
#define LFS_DEBUG(...)
#endif
#endif
#ifndef LFS_INFO
#ifndef LFS_NO_INFO
#define LFS_INFO_(fmt, ...) \
printf("%s:%d:info: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
#define LFS_INFO(...) LFS_INFO_(__VA_ARGS__, "")
#else
#define LFS_INFO(...)
#endif
#endif
#ifndef LFS_WARN
#ifndef LFS_NO_WARN
#define LFS_WARN_(fmt, ...) \
printf("%s:%d:warn: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
#define LFS_WARN(...) LFS_WARN_(__VA_ARGS__, "")
#else
#define LFS_WARN(...)
#endif
#endif
#ifndef LFS_ERROR
#ifndef LFS_NO_ERROR
#define LFS_ERROR_(fmt, ...) \
printf("%s:%d:error: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
#define LFS_ERROR(...) LFS_ERROR_(__VA_ARGS__, "")
#else
#define LFS_ERROR(...)
#endif
#endif
// Runtime assertions
#ifndef LFS_ASSERT
#ifndef LFS_NO_ASSERT
#define LFS_ASSERT(test) assert(test)
#else
#define LFS_ASSERT(test)
#endif
#endif
#ifndef LFS_UNREACHABLE
#ifndef LFS_NO_ASSERT
#define LFS_UNREACHABLE() LFS_ASSERT(false)
#elif !defined(LFS_NO_BUILTINS)
#define LFS_UNREACHABLE() __builtin_unreachable()
#else
#define LFS_UNREACHABLE()
#endif
#endif
// We need to know the endianness of the system for some struct packing
#if (defined(BYTE_ORDER) \
&& defined(ORDER_LITTLE_ENDIAN) \
&& BYTE_ORDER == ORDER_LITTLE_ENDIAN) \
|| (defined(__BYTE_ORDER) \
&& defined(__ORDER_LITTLE_ENDIAN) \
&& __BYTE_ORDER == __ORDER_LITTLE_ENDIAN) \
|| (defined(__BYTE_ORDER__) \
&& defined(__ORDER_LITTLE_ENDIAN__) \
&& __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
#define LFS_LITTLE_ENDIAN
#elif (defined(BYTE_ORDER) \
&& defined(ORDER_BIG_ENDIAN) \
&& BYTE_ORDER == ORDER_BIG_ENDIAN) \
|| (defined(__BYTE_ORDER) \
&& defined(__ORDER_BIG_ENDIAN) \
&& __BYTE_ORDER == __ORDER_BIG_ENDIAN) \
|| (defined(__BYTE_ORDER__) \
&& defined(__ORDER_BIG_ENDIAN__) \
&& __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
#define LFS_BIG_ENDIAN
#else
#error "lfs: Unknown endianness?"
#endif
// Some ifdef conveniences
#ifdef LFS_REVDBG
#define LFS_IFDEF_REVDBG(a, b) (a)
#else
#define LFS_IFDEF_REVDBG(a, b) (b)
#endif
#ifdef LFS_REVNOISE
#define LFS_IFDEF_REVNOISE(a, b) (a)
#else
#define LFS_IFDEF_REVNOISE(a, b) (b)
#endif
#ifdef LFS_CKPROGS
#define LFS_IFDEF_CKPROGS(a, b) (a)
#else
#define LFS_IFDEF_CKPROGS(a, b) (b)
#endif
#ifdef LFS_CKFETCHES
#define LFS_IFDEF_CKFETCHES(a, b) (a)
#else
#define LFS_IFDEF_CKFETCHES(a, b) (b)
#endif
#ifdef LFS_CKPARITY
#define LFS_IFDEF_CKPARITY(a, b) (a)
#else
#define LFS_IFDEF_CKPARITY(a, b) (b)
#endif
#ifdef LFS_CKDATACKSUMS
#define LFS_IFDEF_CKDATACKSUMS(a, b) (a)
#else
#define LFS_IFDEF_CKDATACKSUMS(a, b) (b)
#endif
#ifdef LFS_GC
#define LFS_IFDEF_GC(a, b) (a)
#else
#define LFS_IFDEF_GC(a, b) (b)
#endif
#ifdef LFS_NONDAG
#define LFS_IFDEF_NONDAG(a, b) (a)
#else
#define LFS_IFDEF_NONDAG(a, b) (b)
#endif
// Some function attributes, no way around these
// Force a function to be inlined
#if !defined(LFS_NO_BUILTINS) && defined(__GNUC__)
#define LFS_FORCEINLINE __attribute__((always_inline))
#else
#define LFS_FORCEINLINE
#endif
// Builtin functions, these may be replaced by more efficient
// toolchain-specific implementations. LFS_NO_BUILTINS falls back to a more
// expensive basic C implementation for debugging purposes
//
// Most of the backup implementations are based on the infamous Bit
// Twiddling Hacks compiled by Sean Eron Anderson:
// https://graphics.stanford.edu/~seander/bithacks.html
//
// Compile time min/max
#define LFS_MIN(a, b) ((a < b) ? a : b)
#define LFS_MAX(a, b) ((a > b) ? a : b)
// Min/max functions for unsigned 32-bit numbers
static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
return (a < b) ? a : b;
}
static inline uint32_t lfs_max(uint32_t a, uint32_t b) {
return (a > b) ? a : b;
}
static inline int32_t lfs_smin(int32_t a, int32_t b) {
return (a < b) ? a : b;
}
static inline int32_t lfs_smax(int32_t a, int32_t b) {
return (a > b) ? a : b;
}
// Absolute value of signed numbers
static inline int32_t lfs_abs(int32_t a) {
return (a < 0) ? -a : a;
}
// Swap two variables
#define LFS_SWAP(_t, _a, _b) \
do { \
_t *a = _a; \
_t *b = _b; \
_t t = *a; \
*a = *b; \
*b = t; \
} while (0)
// Align to nearest multiple of a size
static inline uint32_t lfs_aligndown(uint32_t a, uint32_t alignment) {
return a - (a % alignment);
}
static inline uint32_t lfs_alignup(uint32_t a, uint32_t alignment) {
return lfs_aligndown(a + alignment-1, alignment);
}
// Find the smallest power of 2 greater than or equal to a
static inline uint32_t lfs_npw2(uint32_t a) {
// __builtin_clz of zero is undefined, so treat both 0 and 1 specially
if (a <= 1) {
return a;
}
#if !defined(LFS_NO_BUILTINS) && (defined(__GNUC__) || defined(__CC_ARM))
return 32 - __builtin_clz(a-1);
#else
uint32_t r = 0;
uint32_t s;
a -= 1;
s = (a > 0xffff) << 4; a >>= s; r |= s;
s = (a > 0xff ) << 3; a >>= s; r |= s;
s = (a > 0xf ) << 2; a >>= s; r |= s;
s = (a > 0x3 ) << 1; a >>= s; r |= s;
return (r | (a >> 1)) + 1;
#endif
}
// TODO we should eventually adopt this as the new name for npw2
// Find the ceiling of log base 2 of the given number
static inline uint32_t lfs_nlog2(uint32_t a) {
return lfs_npw2(a);
}
// Count the number of trailing binary zeros in a
// lfs_ctz(0) may be undefined
static inline uint32_t lfs_ctz(uint32_t a) {
#if !defined(LFS_NO_BUILTINS) && defined(__GNUC__)
return __builtin_ctz(a);
#else
return lfs_npw2((a & -a) + 1) - 1;
#endif
}
// Count the number of binary ones in a
static inline uint32_t lfs_popc(uint32_t a) {
#if !defined(LFS_NO_BUILTINS) && (defined(__GNUC__) || defined(__CC_ARM))
return __builtin_popcount(a);
#else
a = a - ((a >> 1) & 0x55555555);
a = (a & 0x33333333) + ((a >> 2) & 0x33333333);
a = (a + (a >> 4)) & 0x0f0f0f0f;
return (a * 0x1010101) >> 24;
#endif
}
// Returns true if there is an odd number of binary ones in a
static inline bool lfs_parity(uint32_t a) {
#if !defined(LFS_NO_BUILTINS) && (defined(__GNUC__) || defined(__CC_ARM))
return __builtin_parity(a);
#else
a ^= a >> 16;
a ^= a >> 8;
a ^= a >> 4;
return (0x6996 >> (a & 0xf)) & 1;
#endif
}
// Find the sequence comparison of a and b, this is the distance
// between a and b ignoring overflow
static inline int lfs_scmp(uint32_t a, uint32_t b) {
return (int)(unsigned)(a - b);
}
// Perform polynomial/carry-less multiplication
//
// This is a multiply where all adds are replaced with xors. If we view
// a and b as binary polynomials, xor is polynomial addition and pmul is
// polynomial multiplication.
static inline uint64_t lfs_pmul(uint32_t a, uint32_t b) {
uint64_t r = 0;
uint64_t a_ = a;
while (b) {
if (b & 1) {
r ^= a_;
}
a_ <<= 1;
b >>= 1;
}
return r;
}
// Convert between 32-bit little-endian and native order
static inline uint32_t lfs_fromle32(uint32_t a) {
#if !defined(LFS_NO_BUILTINS) && defined(LFS_LITTLE_ENDIAN)
return a;
#elif !defined(LFS_NO_BUILTINS)
return __builtin_bswap32(a);
#else
return (((uint8_t*)&a)[0] << 0) |
(((uint8_t*)&a)[1] << 8) |
(((uint8_t*)&a)[2] << 16) |
(((uint8_t*)&a)[3] << 24);
#endif
}
static inline uint32_t lfs_tole32(uint32_t a) {
return lfs_fromle32(a);
}
// Convert between 32-bit big-endian and native order
static inline uint32_t lfs_frombe32(uint32_t a) {
#if !defined(LFS_NO_BUILTINS) && defined(LFS_LITTLE_ENDIAN)
return __builtin_bswap32(a);
#elif !defined(LFS_NO_BUILTINS)
return a;
#else
return (((uint8_t*)&a)[0] << 24) |
(((uint8_t*)&a)[1] << 16) |
(((uint8_t*)&a)[2] << 8) |
(((uint8_t*)&a)[3] << 0);
#endif
}
static inline uint32_t lfs_tobe32(uint32_t a) {
return lfs_frombe32(a);
}
// Convert to/from 16-bit little-endian
static inline void lfs_tole16_(uint16_t word, void *buffer) {
((uint8_t*)buffer)[0] = word >> 0;
((uint8_t*)buffer)[1] = word >> 8;
}
static inline uint16_t lfs_fromle16_(const void *buffer) {
return (((uint8_t*)buffer)[0] << 0)
| (((uint8_t*)buffer)[1] << 8);
}
// Convert to/from 32-bit little-endian
static inline void lfs_tole32_(uint32_t word, void *buffer) {
((uint8_t*)buffer)[0] = word >> 0;
((uint8_t*)buffer)[1] = word >> 8;
((uint8_t*)buffer)[2] = word >> 16;
((uint8_t*)buffer)[3] = word >> 24;
}
static inline uint32_t lfs_fromle32_(const void *buffer) {
return (((uint8_t*)buffer)[0] << 0)
| (((uint8_t*)buffer)[1] << 8)
| (((uint8_t*)buffer)[2] << 16)
| (((uint8_t*)buffer)[3] << 24);
}
// Convert to/from leb128 encoding
// TODO should we really be using ssize_t here and not lfs_ssize_t?
ssize_t lfs_toleb128(uint32_t word, void *buffer, size_t size);
ssize_t lfs_fromleb128(uint32_t *word, const void *buffer, size_t size);
// Compare n bytes of memory
#if !defined(LFS_NO_STRINGH)
#define lfs_memcmp memcmp
#elif !defined(LFS_NO_BUILTINS)
#define lfs_memcmp __builtin_memcmp
#else
static inline int lfs_memcmp(const void *a, const void *b, size_t size) {
const uint8_t *a_ = a;
const uint8_t *b_ = b;
for (size_t i = 0; i < size; i++) {
if (a_[i] != b_[i]) {
return (int)a_[i] - (int)b_[i];
}
}
return 0;
}
#endif
// Copy n bytes from src to dst, src and dst must not overlap
#if !defined(LFS_NO_STRINGH)
#define lfs_memcpy memcpy
#elif !defined(LFS_NO_BUILTINS)
#define lfs_memcpy __builtin_memcpy
#else
static inline void *lfs_memcpy(
void *restrict dst, const void *restrict src, size_t size) {
uint8_t *dst_ = dst;
const uint8_t *src_ = src;
for (size_t i = 0; i < size; i++) {
dst_[i] = src_[i];
}
return dst_;
}
#endif
// Copy n bytes from src to dst, src and dst may overlap
#if !defined(LFS_NO_STRINGH)
#define lfs_memmove memmove
#elif !defined(LFS_NO_BUILTINS)
#define lfs_memmove __builtin_memmove
#else
static inline void *lfs_memmove(void *dst, const void *src, size_t size) {
uint8_t *dst_ = dst;
const uint8_t *src_ = src;
if (dst_ < src_) {
for (size_t i = 0; i < size; i++) {
dst_[i] = src_[i];
}
} else if (dst_ > src_) {
for (size_t i = 0; i < size; i++) {
dst_[(size-1)-i] = src_[(size-1)-i];
}
}
return dst_;
}
#endif
// Set n bytes to c
#if !defined(LFS_NO_STRINGH)
#define lfs_memset memset
#elif !defined(LFS_NO_BUILTINS)
#define lfs_memset __builtin_memset
#else
static inline void *lfs_memset(void *dst, int c, size_t size) {
uint8_t *dst_ = dst;
for (size_t i = 0; i < size; i++) {
dst_[i] = c;
}
return dst_;
}
#endif
// Find the first occurrence of c or NULL
#if !defined(LFS_NO_STRINGH)
#define lfs_memchr memchr
#else
static inline void *lfs_memchr(const void *a, int c, size_t size) {
const uint8_t *a_ = a;
for (size_t i = 0; i < size; i++) {
if (a_[i] == c) {
return (void*)&a_[i];
}
}
return NULL;
}
#endif
// Find the first occurrence of anything not c or NULL
static inline void *lfs_memcchr(const void *a, int c, size_t size) {
const uint8_t *a_ = a;
for (size_t i = 0; i < size; i++) {
if (a_[i] != c) {
return (void*)&a_[i];
}
}
return NULL;
}
// Find the minimum length that includes all non-zero bytes
static inline size_t lfs_memlen(const void *a, size_t size) {
const uint8_t *a_ = a;
while (size > 0 && a_[size-1] == 0) {
size -= 1;
}
return size;
}
// Xor n bytes from b into a
static inline void *lfs_memxor(
void *restrict a, const void *restrict b, size_t size) {
uint8_t *a_ = a;
const uint8_t *b_ = b;
for (size_t i = 0; i < size; i++) {
a_[i] ^= b_[i];
}
return a_;
}
// Find the length of a null-terminated string
#if !defined(LFS_NO_STRINGH)
#define lfs_strlen strlen
#else
static inline size_t lfs_strlen(const char *a) {
const char *a_ = a;
while (*a_) {
a_++;
}
return a_ - a;
}
#endif
// Compare two null-terminated strings
#if !defined(LFS_NO_STRINGH)
#define lfs_strcmp strcmp
#else
static inline int lfs_strcmp(const char *a, const char *b) {
while (*a && *a == *b) {
a++;
b++;
}
return (int)*a - (int)*b;
}
#endif
// Copy a null-terminated string from src to dst
#if !defined(LFS_NO_STRINGH)
#define lfs_strcpy strcpy
#else
static inline char *lfs_strcpy(
char *restrict dst, const char *restrict src) {
char *dst_ = dst;
while (*src) {
*dst_ = *src;
dst_++;
src++;
}
*dst_ = '\0';
return dst;
}
#endif
// Find first occurrence of c or NULL
#ifndef LFS_NO_STRINGH
#define lfs_strchr strchr
#else
static inline char *lfs_strchr(const char *a, int c) {
while (*a) {
if (*a == c) {
return (char*)a;
}
a++;
}
return NULL;
}
#endif
// Find first occurrence of anything not c or NULL
static inline char *lfs_strcchr(const char *a, int c) {
while (*a) {
if (*a != c) {
return (char*)a;
}
a++;
}
return NULL;
}
// Find length of a that does not contain any char in cs
#ifndef LFS_NO_STRINGH
#define lfs_strspn strspn
#else
static inline size_t lfs_strspn(const char *a, const char *cs) {
const char *a_ = a;
while (*a_) {
const char *cs_ = cs;
while (*cs_) {
if (*a_ != *cs_) {
return a_ - a;
}
cs_++;
}
a_++;
}
return a_ - a;
}
#endif
// Find length of a that only contains chars in cs
#ifndef LFS_NO_STRINGH
#define lfs_strcspn strcspn
#else
static inline size_t lfs_strcspn(const char *a, const char *cs) {
const char *a_ = a;
while (*a_) {
const char *cs_ = cs;
while (*cs_) {
if (*a_ == *cs_) {
return a_ - a;
}
cs_++;
}
a_++;
}
return a_ - a;
}
#endif
//// Calculate CRC-32 with polynomial = 0x04c11db7
//uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size);
// Odd-parity and even-parity zeros in our crc32c ring
#define LFS_CRC32C_ODDZERO 0xfca42daf
#define LFS_CRC32C_EVENZERO 0x00000000
// Calculate crc32c incrementally
//
// polynomial = 0x11edc6f41
// init = 0xffffffff
// fini = 0xffffffff
//
uint32_t lfs_crc32c(uint32_t crc, const void *buffer, size_t size);
// Multiply two crc32cs in the crc32c ring
uint32_t lfs_crc32c_mul(uint32_t a, uint32_t b);
// Find the cube of a crc32c in the crc32c ring
static inline uint32_t lfs_crc32c_cube(uint32_t a) {
return lfs_crc32c_mul(lfs_crc32c_mul(a, a), a);
}
// Allocate memory, only used if buffers are not provided to littlefs
// Note, memory must be 64-bit aligned
#ifndef LFS_NO_MALLOC
#define lfs_malloc malloc
#else
static inline void *lfs_malloc(size_t size) {
(void)size;
return NULL;
}
#endif
// Deallocate memory, only used if buffers are not provided to littlefs
#ifndef LFS_NO_MALLOC
#define lfs_free free
#else
static inline void lfs_free(void *p) {
(void)p;
}
#endif
#endif
#endif
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