f2fs: compress: add nocompress extensions support

When we create a directory with enable compression, all file write into
directory will try to compress.But sometimes we may know, new file
cannot meet compression ratio requirements.
We need a nocompress extension to skip those files to avoid unnecessary
compress page test.

After add nocompress_extension, the priority should be:
dir_flag < comp_extention,nocompress_extension < comp_file_flag,
no_comp_file_flag.

Priority in between FS_COMPR_FL, FS_NOCOMP_FS, extensions:
   * compress_extension=so; nocompress_extension=zip; chattr +c dir;
     touch dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so
     and baz.txt should be compresse, bar.zip should be non-compressed.
     chattr +c dir/bar.zip can enable compress on bar.zip.
   * compress_extension=so; nocompress_extension=zip; chattr -c dir;
     touch dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so
     should be compresse, bar.zip and baz.txt should be non-compressed.
     chattr+c dir/bar.zip; chattr+c dir/baz.txt; can enable compress on
     bar.zip and baz.txt.

Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 30 insertions, 1 deletions

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index b91e5a8444d5..ff9e7cc97c65 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -281,6 +281,18 @@ 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.
+nocompress_extension=%s	   Support adding specified extension, so that f2fs can disable
+			 compression on those corresponding files, just contrary to compression extension.
+			 If you know exactly which files cannot be compressed, you can use this.
+			 The same extension name can't appear in both compress and nocompress
+			 extension at the same time.
+			 If the compress extension specifies all files, the types specified by the
+			 nocompress extension will be treated as special cases and will not be compressed.
+			 Don't allow use '*' to specifie all file in nocompress extension.
+			 After add nocompress_extension, the priority should be:
+			 dir_flag < comp_extention,nocompress_extension < comp_file_flag,no_comp_file_flag.
+			 See more in compression sections.
+
 compress_chksum		 Support verifying chksum of raw data in compressed cluster.
 compress_mode=%s	 Control file compression mode. This supports "fs" and "user"
 			 modes. In "fs" mode (default), f2fs does automatic compression
@@ -817,13 +829,30 @@ Compression implementation
   all logical blocks in cluster contain valid data and compress ratio of
   cluster data is lower than specified threshold.
 
-- To enable compression on regular inode, there are three ways:
+- To enable compression on regular inode, there are four ways:
 
   * chattr +c file
   * chattr +c dir; touch dir/file
   * mount w/ -o compress_extension=ext; touch file.ext
   * mount w/ -o compress_extension=*; touch any_file
 
+- To disable compression on regular inode, there are two ways:
+
+  * chattr -c file
+  * mount w/ -o nocompress_extension=ext; touch file.ext
+
+- Priority in between FS_COMPR_FL, FS_NOCOMP_FS, extensions:
+
+  * compress_extension=so; nocompress_extension=zip; chattr +c dir; touch
+    dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so and baz.txt
+    should be compresse, bar.zip should be non-compressed. chattr +c dir/bar.zip
+    can enable compress on bar.zip.
+  * compress_extension=so; nocompress_extension=zip; chattr -c dir; touch
+    dir/foo.so; touch dir/bar.zip; touch dir/baz.txt; then foo.so should be
+    compresse, bar.zip and baz.txt should be non-compressed.
+    chattr+c dir/bar.zip; chattr+c dir/baz.txt; can enable compress on bar.zip
+    and baz.txt.
+
 - At this point, compression feature doesn't expose compressed space to user
   directly in order to guarantee potential data updates later to the space.
   Instead, the main goal is to reduce data writes to flash disk as much as