1 SQUASHFS 4.3 - A squashed read-only filesystem for Linux 2 3 Copyright 2002-2014 Phillip Lougher <phillip (a] lougher.demon.co.uk> 4 5 Released under the GPL licence (version 2 or later). 6 7 Welcome to Squashfs 4.3. This is the first release in over 3 years, and 8 there are substantial improvements to stability, new compression options 9 and compressors, speed optimisations, and new options for Mksquashfs/Unsquashfs. 10 11 This is a tools only release, support for Squashfs filesystems is 12 in mainline (2.6.29 and later). 13 14 Changes in Squashfs-tools 4.3 15 ----------------------------- 16 17 1. Stability improvements. Better checking of user input for out of 18 range/invalid values. Better handling of corrupted Squashfs filesystems 19 (Mksquashfs append mode, and Unsquashfs). Better handling of buffer 20 overflow/underflow. 21 22 2. GZIP compressor now supports compression options, allowing different 23 compression levels to be used. 24 25 3. Rewritten LZO compressor with compression options, allowing different 26 LZO algorithms and different compression levels to be used. 27 28 4. New LZ4 compressor (note not yet in mainline kernel) 29 30 5. Better default memory usage for Mksquashfs. Mksquashfs by default now 31 uses 25% of physical memory. 32 33 6. Duplicate checking in Mksquashfs further optimised. With certain 34 "problem filesystems" greater than 2x performance improvement. 35 Filesystems with a lot of duplicates should see at least 10-20% speed 36 improvement. 37 38 7. The -stat option in Unsquashfs now displays the compression options 39 used to generate the original filesystem. Previously -stat only displayed 40 the compression algorithm used. 41 42 8. The file being compressed/uncompressed in Mksquashfs/Unsquashfs is now 43 displayed if CTRL-\ (SIGQUIT from keyboard) typed. 44 45 9. The status of the internal queues/caches in Mksquashfs/Unsquashfs is 46 now displayed if CTRL-\ (SIGQUIT from keyboard) is typed twice within 47 one second. Normally only useful for "power users", but it can be 48 used to discover if there's any bottlenecks affecting performance 49 (the bottleneck will normally be the compressors/fragment compressors). 50 51 10. Miscellaneous new options for Mksquashfs/Unsquashfs to fine tune behaviour. 52 53 11. Fixes for CVE-2012-4024 and CVE-2012-4025. 54 55 Compatiblity 56 ------------ 57 58 Mksquashfs 4.3 generates 4.0 filesystems. These filesystems are fully 59 compatible/interchangable with filesystems generated by Mksquashfs 4.0 and are 60 mountable on 2.6.29 and later kernels. 61 62 Compressors 63 ----------- 64 65 New compression options and compressors are now supported. 66 67 The new options and compressors are: 68 69 1. gzip 70 -Xcompression-level <compression-level> 71 <compression-level> should be 1 .. 9 (default 9) 72 -Xwindow-size <window-size> 73 <window-size> should be 8 .. 15 (default 15) 74 -Xstrategy strategy1,strategy2,...,strategyN 75 Compress using strategy1,strategy2,...,strategyN in turn 76 and choose the best compression. 77 Available strategies: default, filtered, huffman_only, 78 run_length_encoded and fixed 79 80 2. lzo 81 -Xalgorithm <algorithm> 82 Where <algorithm> is one of: 83 lzo1x_1 84 lzo1x_1_11 85 lzo1x_1_12 86 lzo1x_1_15 87 lzo1x_999 (default) 88 -Xcompression-level <compression-level> 89 <compression-level> should be 1 .. 9 (default 8) 90 Only applies to lzo1x_999 algorithm 91 92 3. lz4 93 -Xhc 94 Compress using LZ4 High Compression 95 96 The compression specific options are, obviously, specific to the compressor 97 in question, and you should read the compressor documentation and check 98 their web sites to understand their behaviour. 99 100 In general the defaults used by Mksquashfs for each compressor are optimised 101 to give the best performance for each compressor, where what constitutes 102 best depends on the compressor. For gzip/xz best means highest compression 103 (trying multiple filters/strategies can improve compression, but this is 104 extremely expensive computationally, and hence, not suitable for the defaults), 105 for LZO/LZ4 best means a tradeoff between compression and (de)-compression 106 overhead (LZO/LZ4 by definition are intended for weaker processors). 107 108 New Mksquashfs options 109 ---------------------- 110 111 1. -mem <size> 112 113 Set the amount of memory used by Mksquashfs to <size> bytes. G/M and K 114 post-fixes are supported. 115 116 By default Mksquashfs uses 25% of the physical memory. Increasing 117 this with the -mem option can increase performance (note it does not have 118 any effect on compression). Reducing it can prevent thrashing if the 119 system is busy and there is not 25% of physical memory free (again, note 120 it does not have any effect on compression). 121 122 2. -exit-on-error 123 124 By default Mksquashfs treats certain errors as benign, if these 125 errors occur Mksquashfs prints the error on the console but continues. 126 These errors are typically failure to read a file from the source filesystem. 127 This is deliberate, in many cases users prefer Mksquashfs to flag 128 the error but continue rather than abort what may be hours of compression. 129 130 But there are times where failure to read any file is considered critical, 131 and users (especially in the case of automated scripts where the 132 errors output to the console may be missed) prefer Mksquashfs to exit. 133 134 The new -exit-on-error option can be used in this scenario. This option 135 makes Mksquashfs treat all benign errors as fatal. 136 137 3. -progress 138 139 By default if -info is specified, the progress bar is disabled as it gets 140 in the way. Occasionally you might want the progress bar enabled whilst 141 -info is enabled. This option forces Mksquashfs to output the progress 142 bar when -info is specified. 143 144 4. -Xhelp 145 146 Display the usage text for the currently selected compressor. 147 148 New Unsquashfs options 149 ---------------------- 150 151 1. -u[ser-xattrs] 152 153 Only write user xattrs. This forces Unsquashfs to ignore system xattrs. 154 This is useful when Unsquashing a filesystem as a non-root user, and the 155 filesystem contains system xattrs which are only writable by root. 156 157 Major bugs fixed 158 ---------------- 159 160 1. If Mksquashfs ran out of space in the destination filesystem, this 161 would not cause Mksquashfs to immediately abort, and Mksquashfs would 162 continue to process the source filesystem. Mksquashfs now immediately 163 aborts on out of space in the destination filesystem. 164 165 2. Unsquashfs ignored the maximum number of open files limit, and if that 166 was lower than the default limit for Linux, it would run out of file 167 descriptors. Unsquashfs now limits the number of open files to the 168 limit currently in force (e.g. specified by setrlimit). 169 170 3. If huge numbers of dynamic pseudo files were specified, Mksquashfs 171 could exceed the maximum number of open files limit. This was because 172 Mksquashfs created all the dynamic file processes up front before 173 commencing source filesystem reading and compression. Mksquashfs 174 now creates the dynamic file processes on demand whilst reading 175 and compressing the source filesystem, thus limiting the number of 176 dynamic pseudo file processes in existence at any one time. 177 178 4. When outputting Unsquashfs used to set the permissions of directories 179 as it recursively descended. This in hindsight had an obvious oversight, 180 if a directory had only read permission (or was otherwise restricted), then 181 Unsquashfs would fail to write its contents when descending into it. Fixed 182 by setting directory permissions as Unsquashfs recursively unwinds. 183
