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>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 16ce1ad..65befc6 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -151,8 +151,10 @@ struct f2fs_mount_info {
 	unsigned char compress_level;		/* compress level */
 	bool compress_chksum;			/* compressed data chksum */
 	unsigned char compress_ext_cnt;		/* extension count */
+	unsigned char nocompress_ext_cnt;		/* nocompress extension count */
 	int compress_mode;			/* compression mode */
 	unsigned char extensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN];	/* extensions */
+	unsigned char noextensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* extensions */
 };
 
 #define F2FS_FEATURE_ENCRYPT		0x0001