f2fs: add a sysfs entry to show zone capacity

This patch adds a sysfs entry showing the unusable space in a section
made by zone capacity.
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -580,3 +580,9 @@ Date:		January 2022
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
 Description:	Controls max # of node block writes to be used for roll forward
 		recovery. This can limit the roll forward recovery time.
+
+What:		/sys/fs/f2fs/<disk>/unusable_blocks_per_sec
+Date:		June 2022
+Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
+Description:	Shows the number of unusable blocks in a section which was defined by
+		the zone capacity reported by underlying zoned device.

fs/f2fs/sysfs.c

@@ -713,6 +713,11 @@ static struct f2fs_attr f2fs_attr_##_name = {			\
 	.offset = _offset					\
 }
 
+#define F2FS_RO_ATTR(struct_type, struct_name, name, elname)	\
+	F2FS_ATTR_OFFSET(struct_type, name, 0444,		\
+		f2fs_sbi_show, NULL,				\
+		offsetof(struct struct_name, elname))
+
 #define F2FS_RW_ATTR(struct_type, struct_name, name, elname)	\
 	F2FS_ATTR_OFFSET(struct_type, name, 0644,		\
 		f2fs_sbi_show, f2fs_sbi_store,			\
@@ -811,6 +816,8 @@ F2FS_FEATURE_RO_ATTR(encrypted_casefold);
 #endif /* CONFIG_FS_ENCRYPTION */
 #ifdef CONFIG_BLK_DEV_ZONED
 F2FS_FEATURE_RO_ATTR(block_zoned);
+F2FS_RO_ATTR(F2FS_SBI, f2fs_sb_info, unusable_blocks_per_sec,
+					unusable_blocks_per_sec);
 #endif
 F2FS_FEATURE_RO_ATTR(atomic_write);
 F2FS_FEATURE_RO_ATTR(extra_attr);
@@ -919,6 +926,9 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(moved_blocks_background),
 	ATTR_LIST(avg_vblocks),
 #endif
+#ifdef CONFIG_BLK_DEV_ZONED
+	ATTR_LIST(unusable_blocks_per_sec),
+#endif
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	ATTR_LIST(compr_written_block),
 	ATTR_LIST(compr_saved_block),