f2fs: expose # of overprivision segments

This is useful when checking conditions during checkpoint=disable in Android.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -409,3 +409,8 @@ Description:	Give a way to change checkpoint merge daemon's io priority.
 		I/O priority "3". We can select the class between "rt" and "be",
 		and set the I/O priority within valid range of it. "," delimiter
 		is necessary in between I/O class and priority number.
+
+What:		/sys/fs/f2fs/<disk>/ovp_segments
+Date:		March 2021
+Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
+Description:	Shows the number of overprovision segments.

fs/f2fs/sysfs.c

@@ -91,6 +91,13 @@ static ssize_t free_segments_show(struct f2fs_attr *a,
 			(unsigned long long)(free_segments(sbi)));
 }
 
+static ssize_t ovp_segments_show(struct f2fs_attr *a,
+		struct f2fs_sb_info *sbi, char *buf)
+{
+	return sprintf(buf, "%llu\n",
+			(unsigned long long)(overprovision_segments(sbi)));
+}
+
 static ssize_t lifetime_write_kbytes_show(struct f2fs_attr *a,
 		struct f2fs_sb_info *sbi, char *buf)
 {
@@ -629,6 +636,7 @@ F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, node_io_flag, node_io_flag);
 F2FS_RW_ATTR(CPRC_INFO, ckpt_req_control, ckpt_thread_ioprio, ckpt_thread_ioprio);
 F2FS_GENERAL_RO_ATTR(dirty_segments);
 F2FS_GENERAL_RO_ATTR(free_segments);
+F2FS_GENERAL_RO_ATTR(ovp_segments);
 F2FS_GENERAL_RO_ATTR(lifetime_write_kbytes);
 F2FS_GENERAL_RO_ATTR(features);
 F2FS_GENERAL_RO_ATTR(current_reserved_blocks);
@@ -715,6 +723,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(ckpt_thread_ioprio),
 	ATTR_LIST(dirty_segments),
 	ATTR_LIST(free_segments),
+	ATTR_LIST(ovp_segments),
 	ATTR_LIST(unusable),
 	ATTR_LIST(lifetime_write_kbytes),
 	ATTR_LIST(features),