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3893854000
Pull erofs updates from Gao Xiang:
"In this cycle, inode page cache sharing among filesystems on the same
machine is now supported, which is particularly useful for
high-density hosts running tens of thousands of containers.
In addition, we fully isolate the EROFS core on-disk format from other
optional encoded layouts since the core on-disk part is designed to be
simple, effective, and secure. Users can use the core format to build
unique golden immutable images and import their filesystem trees
directly from raw block devices via DMA, page-mapped DAX devices,
and/or file-backed mounts without having to worry about unnecessary
intrinsic consistency issues found in other generic filesystems by
design. However, the full vision is still working in progress and will
spend more time to achieve final goals.
There are other improvements and bug fixes as usual, as listed below:
- Support inode page cache sharing among filesystems
- Formally separate optional encoded (aka compressed) inode layouts
(and the implementations) from the EROFS core on-disk aligned plain
format for future zero-trust security usage
- Improve performance by caching the fact that an inode does not have
a POSIX ACL
- Improve LZ4 decompression error reporting
- Enable LZMA by default and promote DEFLATE and Zstandard algorithms
out of EXPERIMENTAL status
- Switch to inode_set_cached_link() to cache symlink lengths
- random bugfixes and minor cleanups"
* tag 'erofs-for-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs: (31 commits)
erofs: fix UAF issue for file-backed mounts w/ directio option
erofs: update compression algorithm status
erofs: fix inline data read failure for ztailpacking pclusters
erofs: avoid some unnecessary #ifdefs
erofs: handle end of filesystem properly for file-backed mounts
erofs: separate plain and compressed filesystems formally
erofs: use inode_set_cached_link()
erofs: mark inodes without acls in erofs_read_inode()
erofs: implement .fadvise for page cache share
erofs: support compressed inodes for page cache share
erofs: support unencoded inodes for page cache share
erofs: pass inode to trace_erofs_read_folio
erofs: introduce the page cache share feature
erofs: using domain_id in the safer way
erofs: add erofs_inode_set_aops helper to set the aops
erofs: support user-defined fingerprint name
erofs: decouple `struct erofs_anon_fs_type`
fs: Export alloc_empty_backing_file
erofs: tidy up erofs_init_inode_xattrs()
erofs: add missing documentation about `directio` mount option
...
This part of the documentation inside Documentation/ABI directory attempts to document the ABI between the Linux kernel and userspace, and the relative stability of these interfaces. Due to the everchanging nature of Linux, and the differing maturity levels, these interfaces should be used by userspace programs in different ways. We have four different levels of ABI stability, as shown by the four different subdirectories in this location. Interfaces may change levels of stability according to the rules described below. The different levels of stability are: stable/ This directory documents the interfaces that the developer has defined to be stable. Userspace programs are free to use these interfaces with no restrictions, and backward compatibility for them will be guaranteed for at least 2 years. Most interfaces (like syscalls) are expected to never change and always be available. testing/ This directory documents interfaces that are felt to be stable, as the main development of this interface has been completed. The interface can be changed to add new features, but the current interface will not break by doing this, unless grave errors or security problems are found in them. Userspace programs can start to rely on these interfaces, but they must be aware of changes that can occur before these interfaces move to be marked stable. Programs that use these interfaces are strongly encouraged to add their name to the description of these interfaces, so that the kernel developers can easily notify them if any changes occur (see the description of the layout of the files below for details on how to do this.) obsolete/ This directory documents interfaces that are still remaining in the kernel, but are marked to be removed at some later point in time. The description of the interface will document the reason why it is obsolete and when it can be expected to be removed. removed/ This directory contains a list of the old interfaces that have been removed from the kernel. Every file in these directories will contain the following information: What: Short description of the interface Date: Date created KernelVersion: (Optional) Kernel version this feature first showed up in. Note: git history often provides more accurate version info, so this field may be omitted. Contact: Primary contact for this interface (may be a mailing list) Description: Long description of the interface and how to use it. Users: All users of this interface who wish to be notified when it changes. This is very important for interfaces in the "testing" stage, so that kernel developers can work with userspace developers to ensure that things do not break in ways that are unacceptable. It is also important to get feedback for these interfaces to make sure they are working in a proper way and do not need to be changed further. Note: The fields should be use a simple notation, compatible with ReST markup. Also, the file **should not** have a top-level index, like:: === foo === How things move between levels: Interfaces in stable may move to obsolete, as long as the proper notification is given. Interfaces may be removed from obsolete and the kernel as long as the documented amount of time has gone by. Interfaces in the testing state can move to the stable state when the developers feel they are finished. They cannot be removed from the kernel tree without going through the obsolete state first. It's up to the developer to place their interfaces in the category they wish for it to start out in. Notable bits of non-ABI, which should not under any circumstances be considered stable: - Kconfig. Userspace should not rely on the presence or absence of any particular Kconfig symbol, in /proc/config.gz, in the copy of .config commonly installed to /boot, or in any invocation of the kernel build process. - Kernel-internal symbols. Do not rely on the presence, absence, location, or type of any kernel symbol, either in System.map files or the kernel binary itself. See Documentation/process/stable-api-nonsense.rst.