[PATCH] [RFC] mke2fs: handle flex_bg collision with backup descriptors

[Andreas Dilger <adilger@dilger.ca>]

If the flex_bg allocator is laying out block or inode bitmaps or
inode tables, and collides with previously allocated metadata (for
example the backup superblock or group descriptors) don't reset
the allocator to the beginning of the flex_bg, but rather skip the
intervening blocks if there aren't too many of them.

Otherwise, if a large flex_bg factor is specified (e.g. 131072) the
inode table will hit the backup descriptors in groups 1, 3, 5, 7, 9
and start interleaving with the block and inode bitmaps.  That ends
up producing poorly allocated bitmaps and inode tables that are
interleaved and not contiguous as was intended for flex_bg.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
---
 lib/ext2fs/alloc_tables.c |   17 ++++++++++++-----
 1 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/lib/ext2fs/alloc_tables.c b/lib/ext2fs/alloc_tables.c
index 9f3d4e0..6b4392a 100644
--- a/lib/ext2fs/alloc_tables.c
+++ b/lib/ext2fs/alloc_tables.c
@@ -47,16 +47,17 @@ static blk64_t flexbg_offset(ext2_filsys fs, dgrp_t group, blk64_t start_blk,
 	flexbg = group / flexbg_size;
 	size = rem_grp * elem_size;
 
-	if (size > (int) (fs->super->s_blocks_per_group / 8))
-		size = (int) fs->super->s_blocks_per_group / 8;
+	if (size > (int) (fs->super->s_blocks_per_group / 4))
+		size = (int) fs->super->s_blocks_per_group / 4;
 
 	/*
 	 * Don't do a long search if the previous block
 	 * search is still valid.
 	 */
-	if (start_blk && ext2fs_test_block_bitmap_range2(bmap, start_blk,
-							 elem_size))
-		return start_blk;
+	if (start_blk && ext2fs_get_free_blocks2(fs, start_blk,
+						 start_blk + size, elem_size,
+						 bmap, &first_free) == 0)
+		return first_free;
 
 	start_blk = ext2fs_group_first_block2(fs, flexbg_size * flexbg);
 	last_grp = group | (flexbg_size - 1);
@@ -126,6 +127,8 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
 
 		if (group % flexbg_size)
 			prev_block = ext2fs_block_bitmap_loc(fs, group - 1) + 1;
+		/* FIXME: Take backup group descriptor blocks into account
+		 * if the flexbg allocations will grow to overlap them... */
 		start_blk = flexbg_offset(fs, group, prev_block, bmap,
 					  rem_grps, 1);
 		last_blk = ext2fs_group_last_block2(fs, last_grp);
@@ -157,6 +160,8 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
 		else
 			prev_block = ext2fs_block_bitmap_loc(fs, group) +
 				flexbg_size;
+		/* FIXME: Take backup group descriptor blocks into account
+		 * if the flexbg allocations will grow to overlap them... */
 		start_blk = flexbg_offset(fs, group, prev_block, bmap,
 					  rem_grps, 1);
 		last_blk = ext2fs_group_last_block2(fs, last_grp);
@@ -194,6 +199,8 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
 			prev_block = ext2fs_inode_bitmap_loc(fs, group) +
 				flexbg_size;
 
+		/* FIXME: Take backup group descriptor blocks into account
+		 * if the flexbg allocations will grow to overlap them... */
 		group_blk = flexbg_offset(fs, group, prev_block, bmap,
 					  rem_grps, fs->inode_blocks_per_group);
 		last_blk = ext2fs_group_last_block2(fs, last_grp);
-- 
1.7.3.4