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https://github.com/eledio-devices/thirdparty-littlefs.git
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126ef8b07f
This implements the second step of full dynamic wear-leveling, block allocation randomization. This is the key part the uniformly distributes wear across the filesystem, even through reboots. The entropy actually comes from the filesystem itself, by xoring together all of the CRCs in the metadata-pairs on the filesystem. While this sounds like a ridiculous operation, it's easy to do when we already scan the metadata-pairs at mount time. This gives us a random number we can use for block allocation. Unfortunately it's not a great general purpose random generator as the output only changes every filesystem write. Fortunately that's exactly when we need our allocator. --- Additionally, the randomization created a mess for the testing framework. Fortunately, this method of randomization is deterministic. A very useful property for reproducing bugs.
92 lines
1.8 KiB
C
92 lines
1.8 KiB
C
/*
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* Block device emulated on standard files
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*
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* Copyright (c) 2017, Arm Limited. All rights reserved.
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#ifndef LFS_EMUBD_H
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#define LFS_EMUBD_H
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#include "lfs.h"
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#include "lfs_util.h"
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#ifdef __cplusplus
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extern "C"
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{
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#endif
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// Config options
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#ifndef LFS_EMUBD_READ_SIZE
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#define LFS_EMUBD_READ_SIZE 1
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#endif
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#ifndef LFS_EMUBD_PROG_SIZE
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#define LFS_EMUBD_PROG_SIZE 1
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#endif
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#ifndef LFS_EMUBD_ERASE_SIZE
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#define LFS_EMUBD_ERASE_SIZE 512
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#endif
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#ifndef LFS_EMUBD_TOTAL_SIZE
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#define LFS_EMUBD_TOTAL_SIZE 524288
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#endif
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// The emu bd state
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typedef struct lfs_emubd {
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char *path;
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char *child;
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struct {
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uint64_t read_count;
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uint64_t prog_count;
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uint64_t erase_count;
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} stats;
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struct {
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lfs_block_t blocks[4];
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} history;
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struct {
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uint32_t read_size;
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uint32_t prog_size;
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uint32_t block_size;
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uint32_t block_count;
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} cfg;
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} lfs_emubd_t;
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// Create a block device using path for the directory to store blocks
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int lfs_emubd_create(const struct lfs_config *cfg, const char *path);
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// Clean up memory associated with emu block device
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void lfs_emubd_destroy(const struct lfs_config *cfg);
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// Read a block
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int lfs_emubd_read(const struct lfs_config *cfg, lfs_block_t block,
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lfs_off_t off, void *buffer, lfs_size_t size);
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// Program a block
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//
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// The block must have previously been erased.
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int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
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lfs_off_t off, const void *buffer, lfs_size_t size);
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// Erase a block
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//
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// A block must be erased before being programmed. The
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// state of an erased block is undefined.
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int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block);
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// Sync the block device
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int lfs_emubd_sync(const struct lfs_config *cfg);
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#ifdef __cplusplus
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} /* extern "C" */
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#endif
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#endif
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