Re: [f2fs-dev] [PATCH v2 1/2] f2fs: add compress_mode mount option

[Daeho Jeong <daeho43@gmail.com>]

compression enabled regular files have different formats of node
metadata on disk. So, using the
"compress_mode=user,compress_extension=*" mount option, we want to
make the metadata of files ready for compression and make them
compressed whenever the user wants using new ioctls.

2020년 12월 8일 (화) 오후 12:51, Eric Biggers <ebiggers@kernel.org>님이 작성:
>
> On Tue, Dec 01, 2020 at 01:08:02PM +0900, Daeho Jeong wrote:
> > From: Daeho Jeong <daehojeong@google.com>
> >
> > We will add a new "compress_mode" mount option to control file
> > compression mode. This supports "fs" and "user". In "fs" mode (default),
> > f2fs does automatic compression on the compression enabled files.
> > In "user" mode, f2fs disables the automaic compression and gives the
> > user discretion of choosing the target file and the timing. It means
> > the user can do manual compression/decompression on the compression
> > enabled files using ioctls.
> >
> > Signed-off-by: Daeho Jeong <daehojeong@google.com>
> > ---
> > v2: changed mount option name and added more explanation of mount option
> > ---
> >  Documentation/filesystems/f2fs.rst | 35 ++++++++++++++++++++++++++++++
> >  fs/f2fs/compress.c                 |  2 +-
> >  fs/f2fs/data.c                     |  2 +-
> >  fs/f2fs/f2fs.h                     | 30 +++++++++++++++++++++++++
> >  fs/f2fs/segment.c                  |  2 +-
> >  fs/f2fs/super.c                    | 23 ++++++++++++++++++++
> >  6 files changed, 91 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> > index b8ee761c9922..5eb8d63439ec 100644
> > --- a/Documentation/filesystems/f2fs.rst
> > +++ b/Documentation/filesystems/f2fs.rst
> > @@ -260,6 +260,13 @@ compress_extension=%s     Support adding specified extension, so that f2fs can enab
> >                        For other files, we can still enable compression via ioctl.
> >                        Note that, there is one reserved special extension '*', it
> >                        can be set to enable compression for all files.
> > +compress_mode=%s      Control file compression mode. This supports "fs" and "user"
> > +                      modes. In "fs" mode (default), f2fs does automatic compression
> > +                      on the compression enabled files. In "user" mode, f2fs disables
> > +                      the automaic compression and gives the user discretion of
> > +                      choosing the target file and the timing. The user can do manual
> > +                      compression/decompression on the compression enabled files using
> > +                      ioctls.
> >  inlinecrypt           When possible, encrypt/decrypt the contents of encrypted
> >                        files using the blk-crypto framework rather than
> >                        filesystem-layer encryption. This allows the use of
> > @@ -810,6 +817,34 @@ Compress metadata layout::
> >       | data length | data chksum | reserved |      compressed data       |
> >       +-------------+-------------+----------+----------------------------+
> >
> > +Compression mode
> > +--------------------------
> > +
> > +f2fs supports "fs" and "user" compression modes with "compression_mode" mount option.
> > +With this option, f2fs provides a choice to select the way how to compress the
> > +compression enabled files (refer to "Compression implementation" section for how to
> > +enable compression on a regular inode).
> > +
> > +1) compress_mode=fs
> > +This is the default option. f2fs does automatic compression in the writeback of the
> > +compression enabled files.
> > +
> > +2) compress_mode=user
> > +This disables the automaic compression and gives the user discretion of choosing the
> > +target file and the timing. The user can do manual compression/decompression on the
> > +compression enabled files using F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
> > +ioctls like the below.
> > +
> > +To decompress a file,
> > +
> > +fd = open(filename, O_WRONLY, 0);
> > +ret = ioctl(fd, F2FS_IOC_DECOMPRESS_FILE);
> > +
> > +To compress a file,
> > +
> > +fd = open(filename, O_WRONLY, 0);
> > +ret = ioctl(fd, F2FS_IOC_COMPRESS_FILE);
> > +
>
> Why doesn't compress_mode=user just cause regular files to not inherit the
> compression flag?  Then users could set or clear the compression flag using
> FS_IOC_SETFLAGS, without any need for these new ioctls.
>
> - Eric