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The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm looking for a way to read a SquashFS filesystem from a program. So far, I've know about the in-kernel drivers for it, but I'm sure that a userspace library for it must exist somewhere.

Any language would be fine, but C is preferred. Just mounting the filesystem and using it that way is technically possible, but I'd rather avoid that route because the application I'm looking at would involve working with at least a few dozen archives at any given time. I just downloaded the code tarball from squashfs. Only userland code in C for mksquashfs and unsquashfs.

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There is a tool called unsquashfs which extracts the squashfs image akin to tar. It should be bundled with mksquashfs. It's pretty rough, but it works fine. Maybe I'll turn it into a better-designed C library someday. Squashfs is a highly compressed read-only filesystem for Linux. This package contains the utilities for manipulating squashfs filesystems. Be warned that squashing and unsquashing are painfully slow.

It takes several minutes for a script I wrote to unsquash, modify, and re-squash an 87M stage2.

squashfs header

Learn more. Asked 9 years, 11 months ago. Active 8 years, 5 months ago. Viewed 4k times. Andy Lester Active Oldest Votes. You could probably extract code from unsquashfs.

The SquasFS drivers are already mainlined into the soon to be 2. Yann Ramin Yann Ramin John Kugelman John Kugelman k 59 59 gold badges silver badges bronze badges. Sign up or log in Sign up using Google.A squashfs filesystem consists of a maximum of nine parts, packed together on a byte alignment:. The superblock is the first section of a squashfs archive, and contains important information about the archive, including the locations of other sections of the archive.

Metadata blocks are compressed in 8KiB blocks. A metadata block is prefixed by a u16 header. The highest bit of the header is set if the block is stored uncompressed this will happen if the block grew when compressed, or e. The lower 15 bits specifies the size of the metadata block not including the header on disk.

mksquashfs (1) - Linux Man Pages

To read a metadata block, read a u Read that many bytes. If the data is compressed, uncompress the data. In pseudocode:.

squashfs header

Neither the size on disk, nor the compressed size should exceed 8KiB. The uncompressed size should always be equal to 8KiB, with the exception of the last metadata block of a section, which may have an uncompressed size less than 8KiB. If this section is present, it consists of a single metadata blockwhich is always uncompressed. Datablocks and fragments contain the data which is contained by the files in this archive. A single file's data is stored in a number of data blocks, which are stored sequentially in this section.

Because blocks are stored sequentially, the inode for a file only needs to store the position of the first block, and the compressed sizes of each block. Datablocks do not have headers. Information about the size and position of datablocks is stored in the inode of the file to which the datablocks belong.

Information about the size and position of fragment blocks are stored in the Fragment Tableand the size and offset of fragments within the blocks are stored in the inode of the file to which the fragment belongs. In both the fragment table, and file inodes, the size of a data block is represented by a u The size of the block on disk is described by this u32 when this bit is masked out, though the value should always be less than the max block size 1MiB.

If an entire block is found to be full of zero bytes, the block isn't written to disk. Instead a size of zero is stored in the inode. In this range are stored enough metadata blocks to contain all inodes. All metablocks in the table except for the last block should have an uncompressed size of 8KiB.

Inodes are packed into metadata blocks. Inodes are not aligned to block boundaries, and can therefore span the boundary between metadata blocks. To maximise compression there are different inodes for each item type regular file, directory, device, etc.

To further maximise compression, inodes come in two flavors: simple inode types optimised for frequently occurring items, and extended inode types where extra information has to be stored. If the flag is not set, metadata blocks will be stored compressed if compression decreases the size of the block as described in the metadata block section. Entries in the Inode table are referenced for example, in directory entries with u64 values. The upper 16 bits are unused.

The next 32 bits describe the index of the metadata block. The lower 16 bits describe the uncompressed offset within the metadata block where the inode begins remember that an inode may straddle the border between two metadata blocks.

All Inodes share a common header, which contains some common information, as well as describing the type of Inode which follows. This header has the following structure:. There are seven types of inodes, and each type comes in two variants, a basic variant which is smaller and contains only the most-used properties, and an extended variant which has more properties, and will be used when those less used properties are required e.

Note that some inodes types are variable sized symlinks targets, sizes of file data blocks, etc.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Reverse Engineering Stack Exchange is a question and answer site for researchers and developers who explore the principles of a system through analysis of its structure, function, and operation. It only takes a minute to sign up.

Checking the image that the vendor provides I can see a SquashFS flag on it:. Once extracted the file and checking it with hexdump I found the folowing magic number shsq :. I can't test it since I don't have the image but here's a blog post with some description and source code links which is supposed to handle it:. EDIT : after some struggle with the download site I was able to get the decrypted shsq binary.

I could open it easily with 7-Zip 9. You can find the source code for handling SquashFS in 7z Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 6 years, 10 months ago.

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Active 6 months ago. Viewed 16k times. This is not the first time I found this header, but I couldn't find a solution for extract it. Things I tried so far: All versions of unsquashfs and firmware-mod-tools. Modify the header for a known one that the unsquash tool could recognize. Nucklear Nucklear 2 2 gold badges 7 7 silver badges 17 17 bronze badges. Have you looked to see if the vendor has any GPL code released for this device or others?

FWIW, the firmware-mod-kit was able to extract the squashfs image from the link in Igor Skochinsky's answer, which has the same magic bytes. Actually firmware-mod-kit does support LZMA.You can help to improve this page by adding explanations for the different firmware types below. If you are confused by the many different firmware types and extensions in the OpenWrt firmware downloads table, this pages tries to explain a bit about this topic.

Use when flashing from OEM non-openwrt 1. If only a sysupgrade image is available for your router, either the router is already running some kind of OpenWrt fork which understands the sysupgrade format natively or web flash via the OEM UI is not possible… Please consult the Table of Hardware for your device for installation instructions from OEM firmware. Commonly used when upgrading. This firmware contains a type of partition that is compressed and mounts read-only. All modifications file edit, new files, deleted files are committed to an overlay.

`squashfs-tools` creates incorrectly compressed file

Can be loaded from an arbitrary location most often tftp and is self-contained in memory. This is like a Linux LiveCD. Often used to test firmware, as the first part of a multi-stage installation or as a recovery tool.

Optimizing SquashFS at the Kernel Level (up to Android 9)

An initramfs and initrd are basically the same. Both can have a uHeader, to let uBoot know what it is. The initramfs-kernel image is used for development or special situations as a one-time boot as a stepping stone toward installing the regular sysupgrade version. Since the initramfs version runs entirely from RAM, it does not store any settings in flash, so it is not suitable for operational use.

Designed to be loaded from tftp server. Device in recovery mode? This is an image format designed for U-Boot loader. Same as initramfs-or-uImage? This is an image format designed for U-Boot loader, generally consisting of a kernel with a header for information.

Further is contains a description of the actual contents linux kernel, version, …. Some extra code which can decompress the kernel before booting it. SDK Toolchain for compiling single userspace packages 4. To build custom images without compiling 5. For OpenWrt Flash Layout see: flash. Binwalk can help to analyze unknown formats. User Tools Register Log In.

Site Tools Search. Sidebar Welcome to the OpenWrt Project. Supported Devices. Quick start guide. User guide. Developer guide. Submitting patches. Wiki contribution guide. Table of Contents Image formats.The result would be less data to download for the end user. This describes how to test the boot of a squashfs root image, including build of image and boot in kvm.

Do note that above the '1. The filesystem shows approximately M taken on a wily image. Skip to content.

Instantly share code, notes, and snippets. Code Revisions Embed What would you like to do? Embed Embed this gist in your website. Share Copy sharable link for this gist. Learn more about clone URLs. Download ZIP. To accomplish this, the following work items would need to be done: cloud-images build to produce a squashfs image as lxd-root. Alternatively, the cloud-image build process could produce these artifacts and maas-images simply mirror them also.

This is admittedly primarily dev use only.

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Essentially this does a boot and then a full read of the filesystem. TarInfo t. Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. You signed in with another tab or window.

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Reload to refresh your session. You signed out in another tab or window. Start of a "squashfs to tar" program.SquashFS is a compressed read-only filesystem for Linux. The file system is read-only by design and thus suitable for use on the system partition. Many Android devices may benefit from using this file system for their system partition, for example, the following:.

The following optimizations have been implemented to improve the performance of SquashFS. When reading a block default KSquashFS tries to grab all the pages covering this block. If a single page is up-to-date or locked, it falls back to allocating a full block, submitting a read request, and then copying its content to the pages. This approach is very ineffective; after some time the page cache is likely to contain pages that are up-to-date even if the adjacent pages are not.

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This improves performance in the following ways:. There are two problems with this approach:. SquashFS does not implement. Now that our read requests are asynchronous, the kernel can truly prefetch pages using its asynchronous read-ahead mechanism. Modern systems such as Android contain a lot of files that are already compressed. As a consequence, the image contains a lot of blocks that can't be compressed.

SquashFS handles compressed and uncompressed blocks using the same logic: when asked to read a single page, it actually reads a full block default k. While this is necessary for compressed blocks, it is just a waste of resources for uncompressed blocks.

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Instead of reading a full block, SquashFS now just reads what is advised by the readahead algorithm. Content and code samples on this page are subject to the licenses described in the Content License.

Overview Modular System Components. Modular Kernels. HIDL General. HIDL Java. ConfigStore HAL. Device Tree Overlays.

Vendor NDK. Vendor Interface Object. Many Android devices may benefit from using this file system for their system partition, for example, the following: Devices with a low capacity storage such as Android Watch.

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Unfortunately the performance of SquashFS lags behind ext4. Optimizations The following optimizations have been implemented to improve the performance of SquashFS. Reduce the memory usage and memcpy When reading a block default KSquashFS tries to grab all the pages covering this block. There are two problems with this approach: As the name implies, the function waits for the reads to complete before returning. This is redundant since.You seem to have CSS turned off. Please don't fill out this field.

Please provide the ad click URL, if possible:. Help Create Join Login. Operations Management. IT Management. Project Management. Services Business VoIP. Resources Blog Articles Deals. Menu Help Create Join Login. Home Browse squashfs - a compressed fs for Linux Mailing Lists.

Re: [Squashfs-devel] squashfs xattr support? Attachments: Add-extended-attributes-for-squashfs.

squashfs header

Attachments: squashfs-xattr-filesystem-layout. Re: [Squashfs-devel] [RFC] mksquashfs support for xattr. Oh no! Some styles failed to load. Sign Up No, Thank you. Thanks for helping keep SourceForge clean. X You seem to have CSS turned off.

Briefly describe the problem required :. Upload screenshot of ad required :. Vyatta uses squashfs both for livecd and installed image mode, and in order to support SELinux properly we need xattr supported on squashfs. I know the current version of squashfs doesn't support xattr, and there are hints of future support. But we need it sooner, does anybody have a "back of the envelope" description of how they expect it to work data formats etcI am perfectly willing to fill in the missing code.

I have similar requirements and have a tentative squashfs xattr implementation. I will clean up the code and publish it for review tomorrow, so you are welcome to try it out and comment on it. This allows up to Kb of compressed xattr data per filesystem, and a conceptually unlimited size of individual attributes and attribute sets.