Re: [RFC PATCH v3 00/12] fs: interface for directly reading/writing compressed data

[Omar Sandoval <osandov@osandov.com>]

On Wed, Nov 20, 2019 at 10:24:20AM -0800, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> Hello,
> 
> This series adds an API for reading compressed data on a filesystem
> without decompressing it as well as support for writing compressed data
> directly to the filesystem. As with the previous submissions, I've
> included a man page patch describing the API, and test cases and example
> programs are available [1].
> 
> This version reworks the VFS interface to be backward and forward
> compatible and support for writing inline and bookend extents to the
> Btrfs implementation.
> 
> Patches 1-3 add the VFS support. Patches 4-7 are Btrfs cleanups
> necessary for the encoded I/O support that can go in independently of
> this series. Patches 8-10 are Btrfs prep patches. Patch 11 adds Btrfs
> encoded read support and patch 12 adds Btrfs encoded write support.
> 
> A few TODOs remain:
> 
> - Once we've settled on the interface, I'll add RWF_ENCODED support to
>   fsstress and friends and send up the xfstests patches in [1].
> - btrfs_encoded_read() still doesn't implement repair.
> 
> Changes from v2 [2]:
> 
> - Rebase on v5.4-rc8
> - Add patch 1 introducing copy_struct_from_iter() as suggested by Aleksa
> - Rename O_ENCODED to O_ALLOW_ENCODED as suggested by Amir
> - Add arch-specific definitions of O_ALLOW_ENCODED for alpha, parisc,
>   and sparc
> - Rework the VFS interface to be backward and forward compatible
> - Document the VFS interface as requested by Dave
> - Use __aligned_u64 for struct encoded_iov as noted by Aleksa
> - Fix len/unencoded_len mixup in mm/filemap.c as noted by Nikolay
> - Add support for writing inline and bookend extents to Btrfs
> - Use ENOBUFS for "buffers not big enough for encoded extent" case and
>   E2BIG for "encoded_iov has unsupported fields" case
> 
> Please share any comments on the API or implementation. Thanks!
> 
> 1: https://github.com/osandov/xfstests/tree/rwf-encoded
> 2: https://lore.kernel.org/linux-btrfs/cover.1571164762.git.osandov@fb.com/
> 
> Omar Sandoval (12):
>   iov_iter: add copy_struct_from_iter()
>   fs: add O_ALLOW_ENCODED open flag
>   fs: add RWF_ENCODED for reading/writing compressed data
>   btrfs: get rid of trivial __btrfs_lookup_bio_sums() wrappers
>   btrfs: don't advance offset for compressed bios in
>     btrfs_csum_one_bio()
>   btrfs: remove dead snapshot-aware defrag code
>   btrfs: make btrfs_ordered_extent naming consistent with
>     btrfs_file_extent_item
>   btrfs: add ram_bytes and offset to btrfs_ordered_extent
>   btrfs: support different disk extent size for delalloc
>   btrfs: optionally extend i_size in cow_file_range_inline()
>   btrfs: implement RWF_ENCODED reads
>   btrfs: implement RWF_ENCODED writes
> 
>  Documentation/filesystems/encoded_io.rst |   79 +
>  Documentation/filesystems/index.rst      |    1 +
>  arch/alpha/include/uapi/asm/fcntl.h      |    1 +
>  arch/parisc/include/uapi/asm/fcntl.h     |    1 +
>  arch/sparc/include/uapi/asm/fcntl.h      |    1 +
>  fs/btrfs/compression.c                   |   15 +-
>  fs/btrfs/compression.h                   |    5 +-
>  fs/btrfs/ctree.h                         |   13 +-
>  fs/btrfs/delalloc-space.c                |   38 +-
>  fs/btrfs/delalloc-space.h                |    4 +-
>  fs/btrfs/file-item.c                     |   54 +-
>  fs/btrfs/file.c                          |   61 +-
>  fs/btrfs/inode.c                         | 2463 +++++++++++-----------
>  fs/btrfs/ordered-data.c                  |  106 +-
>  fs/btrfs/ordered-data.h                  |   28 +-
>  fs/btrfs/relocation.c                    |    9 +-
>  fs/fcntl.c                               |   10 +-
>  fs/namei.c                               |    4 +
>  include/linux/fcntl.h                    |    2 +-
>  include/linux/fs.h                       |   16 +
>  include/linux/uio.h                      |    2 +
>  include/trace/events/btrfs.h             |    6 +-
>  include/uapi/asm-generic/fcntl.h         |    4 +
>  include/uapi/linux/fs.h                  |   33 +-
>  lib/iov_iter.c                           |   82 +
>  mm/filemap.c                             |  165 +-
>  26 files changed, 1807 insertions(+), 1396 deletions(-)
>  create mode 100644 Documentation/filesystems/encoded_io.rst

Ping. Al, would you mind taking a look at the generic bits/interface?