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Subject[PATCH 00/25] staging: erofs: introduce erofs file system

This is actually the 2nd patchset of erofs file system,
the original patchset can be found at


In order to keep up with the mainline linux-kernel changes and
improve it in a more active and timely manner, we put forword
this upstream proposal for linux-staging.

EROFS file system is a read-only file system with compression
support designed for certain devices (especially embeded
devices) with very limited physical memory and lots of memory
consumers, such as Android devices. It aimes to provide
a complete compression solution for such devices focuing
on high performance and little extra memory overhead.

It is perferred to select larger compressed cluster sizes
(generally >= 128k) for traditional compression file systems.
It reads and decompresses a large compressed cluster at once,
which has a good-looking random read number when memory
is sufficient because all historial decompressed data
is expected to be cached in memory. However, it also
induces destructive effects when such devices have no enough
spare memory for caching and decompression.

EROFS file system acts in some different way. It uses
fixed-sized compressed size rather than fixed-sized input
size, namely VLE (variable-length extent) compression,
which has at least three adventages:

1) all data read from block device at once can be
utilized, and read amplification can be easier to
estimate and control;
2) generally, it has a better compression ratio than
fixed-sized input compression approaches configured
with the same size;
3) aggressively optimized paths such as partial page
read can be implemented to gain better performance
for page-unaligned read (unimplemented yet, in TODO list).

As can be seen, VLE compression does a great job in small
compressed cluster sizes, which is of course suitable for
devices with limited memory. In this patchset, an in-place
decompresion is also introduced to minimize extra memory usage.

Apart from compression, EROFS also has the following features
available and some limits:
o page-sized block support (currently, and no buffer-head);
o 32-bit block address (16TB for 4KB block);
o selectable v1 (32 bytes) / v2 (64 bytes) inode;
o 32-bit / 64-bit file size;
o 64-bit node number for addressing inodes;
o 64-bit s and 32-bit ns timestamps;
o inline data support;
o inline and shared xattr support;
o metadata and data can be mixed (optional);
o special inode support;
o posix acl support.

The file system is still actively WIP, see _TODO_ for more details.

Any comments are welcome. :)

Change log from the original patchset

o Introduce a new erofs decompression subsystem, which has
better sequencial read than the original patchset, and
its random read remains almost the same (note that erofs
still only fully support page-sized compressed cluster as
the compression unit, however some additional code enabling
larger compressed clustersizes is also added in this version);

o Avoid LINUX_VERSION macros for linux-staging upstream

o several bugfix and cleanup

Short log

Chao Yu (3):
staging: erofs: support special inode
staging: erofs: introduce error injection infrastructure
staging: erofs: support tracepoint

Gao Xiang (22):
staging: erofs: add on-disk layout
staging: erofs: add erofs in-memory stuffs
staging: erofs: add super block operations
staging: erofs: add raw address_space operations
staging: erofs: add inode operations
staging: erofs: add directory operations
staging: erofs: add namei functions
staging: erofs: update Kconfig and Makefile
staging: erofs: introduce xattr & acl support
staging: erofs: <linux/tagptr.h>: introduce tagged pointer
staging: erofs: introduce pagevec for unzip subsystem
staging: erofs: add erofs_map_blocks_iter
staging: erofs: add erofs_allocpage
staging: erofs: globalize prepare_bio and __submit_bio
staging: erofs: introduce a customized LZ4 decompression
staging: erofs: add a generic z_erofs VLE decompressor
staging: erofs: introduce superblock registration
staging: erofs: introduce erofs shrinker
staging: erofs: introduce workstation for decompression
staging: erofs: introduce VLE decompression support
staging: erofs: introduce cached decompression
staging: erofs: add a TODO and update MAINTAINERS for staging

drivers/staging/Kconfig | 2 +
drivers/staging/Makefile | 1 +
drivers/staging/erofs/Kconfig | 141 ++
drivers/staging/erofs/Makefile | 13 +
drivers/staging/erofs/TODO | 45 +
drivers/staging/erofs/data.c | 385 +++++
drivers/staging/erofs/dir.c | 145 ++
drivers/staging/erofs/erofs_fs.h | 266 ++++
drivers/staging/erofs/include/linux/tagptr.h | 110 ++
drivers/staging/erofs/include/trace/events/erofs.h | 240 +++
drivers/staging/erofs/inode.c | 283 ++++
drivers/staging/erofs/internal.h | 556 +++++++
drivers/staging/erofs/lz4defs.h | 227 +++
drivers/staging/erofs/namei.c | 251 +++
drivers/staging/erofs/super.c | 649 ++++++++
drivers/staging/erofs/unzip_lz4.c | 251 +++
drivers/staging/erofs/unzip_pagevec.h | 172 +++
drivers/staging/erofs/unzip_vle.c | 1634 ++++++++++++++++++++
drivers/staging/erofs/unzip_vle.h | 239 +++
drivers/staging/erofs/unzip_vle_lz4.c | 209 +++
drivers/staging/erofs/utils.c | 270 ++++
drivers/staging/erofs/xattr.c | 579 +++++++
drivers/staging/erofs/xattr.h | 93 ++
24 files changed, 6768 insertions(+)
create mode 100644 drivers/staging/erofs/Kconfig
create mode 100644 drivers/staging/erofs/Makefile
create mode 100644 drivers/staging/erofs/TODO
create mode 100644 drivers/staging/erofs/data.c
create mode 100644 drivers/staging/erofs/dir.c
create mode 100644 drivers/staging/erofs/erofs_fs.h
create mode 100644 drivers/staging/erofs/include/linux/tagptr.h
create mode 100644 drivers/staging/erofs/include/trace/events/erofs.h
create mode 100644 drivers/staging/erofs/inode.c
create mode 100644 drivers/staging/erofs/internal.h
create mode 100644 drivers/staging/erofs/lz4defs.h
create mode 100644 drivers/staging/erofs/namei.c
create mode 100644 drivers/staging/erofs/super.c
create mode 100644 drivers/staging/erofs/unzip_lz4.c
create mode 100644 drivers/staging/erofs/unzip_pagevec.h
create mode 100644 drivers/staging/erofs/unzip_vle.c
create mode 100644 drivers/staging/erofs/unzip_vle.h
create mode 100644 drivers/staging/erofs/unzip_vle_lz4.c
create mode 100644 drivers/staging/erofs/utils.c
create mode 100644 drivers/staging/erofs/xattr.c
create mode 100644 drivers/staging/erofs/xattr.h

Gao Xiang


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