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@@ -177,39 +177,41 @@ struct lfs_config {
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lfs_size_t prog_size;
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// Size of an erasable block. This does not impact ram consumption and
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- // may be larger than the physical erase size. However, this should be
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- // kept small as each file currently takes up an entire block.
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- // Must be a multiple of the read, program, and cache sizes.
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+ // may be larger than the physical erase size. However, non-inlined files
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+ // take up at minimum one block. Must be a multiple of the read
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+ // and program sizes.
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lfs_size_t block_size;
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// Number of erasable blocks on the device.
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lfs_size_t block_count;
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// Number of erase cycles before we should move data to another block.
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- // May be zero to never move data, in which case no block-level
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- // wear-leveling is performed.
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+ // May be zero, in which case no block-level wear-leveling is performed.
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uint32_t block_cycles;
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// Size of block caches. Each cache buffers a portion of a block in RAM.
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- // This determines the size of the read cache, the program cache, and a
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+ // The littlefs needs a read cache, a program cache, and one additional
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// cache per file. Larger caches can improve performance by storing more
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- // data. Must be a multiple of the read and program sizes.
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+ // data and reducing the number of disk accesses. Must be a multiple of
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+ // the read and program sizes, and a factor of the block size.
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lfs_size_t cache_size;
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- // Number of blocks to lookahead during block allocation. A larger
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- // lookahead reduces the number of passes required to allocate a block.
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- // The lookahead buffer requires only 1 bit per block so it can be quite
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- // large with little ram impact. Should be a multiple of 32.
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- lfs_size_t lookahead;
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+ // Size of the lookahead buffer in bytes. A larger lookahead buffer
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+ // increases the number of blocks found during an allocation pass. The
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+ // lookahead buffer is stored as a compact bitmap, so each byte of RAM
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+ // can track 8 blocks. Must be a multiple of 4.
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+ lfs_size_t lookahead_size;
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- // Optional, statically allocated read buffer. Must be read sized.
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+ // Optional statically allocated read buffer. Must be cache_size.
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+ // By default lfs_malloc is used to allocate this buffer.
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void *read_buffer;
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- // Optional, statically allocated program buffer. Must be program sized.
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+ // Optional statically allocated program buffer. Must be cache_size.
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+ // By default lfs_malloc is used to allocate this buffer.
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void *prog_buffer;
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- // Optional, statically allocated lookahead buffer. Must be 1 bit per
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- // lookahead block.
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+ // Optional statically allocated program buffer. Must be lookahead_size.
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+ // By default lfs_malloc is used to allocate this buffer.
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void *lookahead_buffer;
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// Optional upper limit on length of file names in bytes. No downside for
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@@ -266,11 +268,11 @@ struct lfs_attr {
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// Optional configuration provided during lfs_file_opencfg
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struct lfs_file_config {
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- // Optional, statically allocated buffer for files. Must be program sized.
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- // If NULL, malloc will be used by default.
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+ // Optional statically allocated file buffer. Must be cache_size.
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+ // By default lfs_malloc is used to allocate this buffer.
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void *buffer;
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- // Optional, linked list of custom attributes related to the file. If the
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+ // Optional linked list of custom attributes related to the file. If the
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// file is opened with read access, the attributes will be read from
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// during the open call. If the file is opened with write access, the
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// attributes will be written to disk every file sync or close. This
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Christopher Haster