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 <[email protected]>님이 작성:
>
> On Tue, Dec 01, 2020 at 01:08:02PM +0900, Daeho Jeong wrote:
> > From: Daeho Jeong <[email protected]>
> >
> > 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 <[email protected]>
> > ---
> > 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