Lines Matching +full:cache +full:- +full:block +full:- +full:size
1 .. SPDX-License-Identifier: GPL-2.0
7 Squashfs is a compressed read-only filesystem for Linux.
11 minimise data overhead. Block sizes greater than 4K are supported up to a
12 maximum of 1Mbytes (default block size 128K).
14 Squashfs is intended for general read-only filesystem use, for archival
16 block device/memory systems (e.g. embedded systems) where low overhead is
19 Mailing list (kernel code): linux-fsdevel@vger.kernel.org
20 Web site: github.com/plougher/squashfs-tools
23 ----------------------
30 Max filesystem size 2^64 256 MiB
31 Max file size ~ 2 TiB 16 MiB
35 Max block size 1 MiB 4 KiB
39 Tail-end packing (fragments) yes no
44 32-bit uids/gids yes no
53 file type, i.e. regular file, directory, symbolic link, and block/char device
57 -----------------
59 As squashfs is a read-only filesystem, the mksquashfs program must be used to
61 are very likely packaged by your linux distribution (called squashfs-tools).
62 The source code can be obtained from github.com/plougher/squashfs-tools.
66 -----------------
86 single use single-threaded decompression (default)
88 Only one block (data or metadata) can be
104 decompression is load-balanced across the
126 -----------------------------
131 ---------------
133 |---------------|
136 |---------------|
139 |---------------|
141 |---------------|
144 |---------------|
147 |---------------|
150 |---------------|
153 |---------------|
156 ---------------
164 -----------------------
167 dictionary size). If non-default compression options have been used, then
171 ----------
174 compressed block is prefixed by a two byte length, the top bit is set if the
175 block is uncompressed. A block will be uncompressed if the -noI option is set,
176 or if the compressed block was larger than the uncompressed block.
178 Inodes are packed into the metadata blocks, and are not aligned to block
180 by a 48-bit number which encodes the location of the compressed metadata block
181 containing the inode, and the byte offset into that block where the inode is
182 placed (<block, offset>).
194 ---------------
199 decompressed block (<block, offset>).
204 compressed metadata block, and therefore, can share the start block.
206 header containing the shared start block value, and a sequence of directory
207 entries, each of which share the shared start block. A new directory header
208 is written once/if the inode start block changes. The directory
214 in each metadata block. Directories are sorted in alphabetical order,
217 location of the metadata block the filename is in has been found.
218 The general idea of the index is to ensure only one metadata block needs to be
224 -------------
227 compressed fragment block (tail-end packed block). The compressed size
228 of each datablock is stored in a block list contained within the
232 larger), the code implements an index cache that caches the mapping from
233 block index to datablock location on disk.
235 The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
236 retaining a simple and space-efficient block list on disk. The cache
239 The index cache is designed to be memory efficient, and by default uses
243 -------------------------
246 location on disk and compressed size using a fragment lookup table. This
253 ------------------------
256 converted to 32-bit uids/gids using an id look up table. This table is
262 ----------------
265 can optionally (disabled with the -no-exports Mksquashfs option) contain
276 ---------------
287 also allows values to be de-duplicated, the value being stored once, and
291 To reduce overhead in inodes, rather than storing the on-disk
292 location of the xattr list inside each inode, a 32-bit xattr id
297 -------------------------------
300 -------------
304 4.2 Squashfs Internal Cache
305 ---------------------------
310 The cache is not used for file datablocks, these are decompressed and cached in
311 the page-cache in the normal way. The cache is used to temporarily cache
316 which have been packed with it, these because of locality-of-reference may be
320 In the future this internal cache may be replaced with an implementation which
321 uses the kernel page cache. Because the page cache operates on page sized