f2fs: add carve_out sysfs node

For several zoned storage devices, vendors will provide extra space
which was used for device level GC than specs and F2FS can use this
space for filesystem level GC. To do that, we can reserve the space
using reserved_blocks. However, it is not enough, since this extra
space should not be shown to users. So, with this new sysfs node,
we can hide the space by substracting reserved_blocks from total
bytes.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: Daeho Jeong

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -836,3 +836,13 @@ Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
 Description:	It reclaims the given KBs of file-backed pages registered by
 		ioctl(F2FS_IOC_DONATE_RANGE).
 		For example, writing N tries to drop N KBs spaces in LRU.
+
+What:		/sys/fs/f2fs/<disk>/carve_out
+Date:		March 2025
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	For several zoned storage devices, vendors will provide extra space which
+		was used for device level GC than specs and F2FS can use this space for
+		filesystem level GC. To do that, we can reserve the space using
+		reserved_blocks. However, it is not enough, since this extra space should
+		not be shown to users. So, with this new sysfs node, we can hide the space
+		by substracting reserved_blocks from total bytes.

fs/f2fs/f2fs.h

@@ -1813,6 +1813,9 @@ struct f2fs_sb_info {
 	u64 committed_atomic_block;
 	u64 revoked_atomic_block;
 
+	/* carve out reserved_blocks from total blocks */
+	bool carve_out;
+
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	struct kmem_cache *page_array_slab;	/* page array entry */
 	unsigned int page_array_slab_size;	/* default page array slab size */

fs/f2fs/super.c

@@ -1849,7 +1849,8 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	buf->f_blocks = total_count - start_count;
 
 	spin_lock(&sbi->stat_lock);
-
+	if (sbi->carve_out)
+		buf->f_blocks -= sbi->current_reserved_blocks;
 	user_block_count = sbi->user_block_count;
 	total_valid_node_count = valid_node_count(sbi);
 	avail_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;

fs/f2fs/sysfs.c

@@ -1122,6 +1122,7 @@ F2FS_SBI_GENERAL_RW_ATTR(max_read_extent_count);
 F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
 F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
 #endif
+F2FS_SBI_GENERAL_RW_ATTR(carve_out);
 
 /* STAT_INFO ATTR */
 #ifdef CONFIG_F2FS_STAT_FS
@@ -1309,6 +1310,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(warm_data_age_threshold),
 	ATTR_LIST(last_age_weight),
 	ATTR_LIST(max_read_extent_count),
+	ATTR_LIST(carve_out),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);