[PATCH v2] libf2fs: Fix calculation of usable segments for single

[Yonggil Song <yonggil.song@samsung.com>]

There was a problem that did not subtract the super block area when calculating
the usable segments for a single zoned device with a conventional zone.
This resulted in incorrect the overprovision and reserved area.

	<256MiB legacy block + zoned block w/ 32MiB zone size>
	Info: Overprovision ratio = 3.570%
	Info: Overprovision segments = 656 (GC reserved = 560)

	<8 conventional zone + 1016 sequential zone w/ 32MiB zone size>
	Info: Overprovision ratio = 3.700%
	Info: Overprovision segments = 676 (GC reserved = 578)

This patch addresses the problem by subtracting the super block area when
there is only one zoned device.

Signed-off-by: Yonggil Song <yonggil.song@samsung.com>
---
 lib/libf2fs_zoned.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/libf2fs_zoned.c b/lib/libf2fs_zoned.c
index 89ba5ad73a76..1a0985378789 100644
--- a/lib/libf2fs_zoned.c
+++ b/lib/libf2fs_zoned.c
@@ -555,6 +555,11 @@ uint32_t f2fs_get_usable_segments(struct f2fs_super_block *sb)
 	}
 	usable_segs -= (get_sb(main_blkaddr) - get_sb(segment0_blkaddr)) >>
 						get_sb(log_blocks_per_seg);
+
+	/* single zoned device needs to remove a super block area */
+	if (c.ndevs == 1 && c.devices[0].zoned_model == F2FS_ZONED_HM)
+		usable_segs -= (get_sb(segment0_blkaddr) >> get_sb(log_blocks_per_seg));
+
 	return usable_segs;
 #endif
 	return get_sb(segment_count_main);
-- 
2.43.0