mirror of https://gitee.com/openkylin/linux.git
27 lines
1002 B
ReStructuredText
27 lines
1002 B
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.. SPDX-License-Identifier: GPL-2.0
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High Level Design
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=================
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An ext4 file system is split into a series of block groups. To reduce
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performance difficulties due to fragmentation, the block allocator tries
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very hard to keep each file's blocks within the same group, thereby
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reducing seek times. The size of a block group is specified in
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``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 \*
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``block_size_in_bytes``. With the default block size of 4KiB, each group
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will contain 32,768 blocks, for a length of 128MiB. The number of block
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groups is the size of the device divided by the size of a block group.
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All fields in ext4 are written to disk in little-endian order. HOWEVER,
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all fields in jbd2 (the journal) are written to disk in big-endian
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order.
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.. include:: blocks.rst
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.. include:: blockgroup.rst
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.. include:: special_inodes.rst
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.. include:: allocators.rst
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.. include:: checksums.rst
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.. include:: bigalloc.rst
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.. include:: inlinedata.rst
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.. include:: eainode.rst
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