[PATCH] resize2fs: Make minimum size estimates more reliable for mounted fs

[Jan Kara <jack@suse.cz>]

Currently, the estimate of minimum filesystem size is using free blocks
counter in the superblock. The counter generally doesn't get updated
while the filesystem is mounted and thus the estimate is very unreliable
for a mounted filesystem. For some usecases such as automated
partitioning proposal to the user it is desirable that the estimate of
minimum filesystem size is reasonably accurate even for a mounted
filesystem. So use group descriptor counters of free blocks for the
estimate of minimum filesystem size. These get updated together with
block being allocated and so the resulting estimate is more accurate.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 resize/resize2fs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index c2e10471bfd1..8a3d08db19f3 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -2926,11 +2926,11 @@ blk64_t calculate_minimum_resize_size(ext2_filsys fs, int flags)
 			fs->super->s_reserved_gdt_blocks;
 
 	/* calculate how many blocks are needed for data */
-	data_needed = ext2fs_blocks_count(fs->super) -
-		ext2fs_free_blocks_count(fs->super);
-
-	for (grp = 0; grp < fs->group_desc_count; grp++)
+	data_needed = ext2fs_blocks_count(fs->super);
+	for (grp = 0; grp < fs->group_desc_count; grp++) {
 		data_needed -= calc_group_overhead(fs, grp, old_desc_blocks);
+		data_needed -= ext2fs_bg_free_blocks_count(fs, grp);
+	}
 #ifdef RESIZE2FS_DEBUG
 	if (flags & RESIZE_DEBUG_MIN_CALC)
 		printf("fs requires %llu data blocks.\n", data_needed);
-- 
2.16.4