Properly calculate overhead in ext2fs_initialize()

For some odd geometries*, mkfs will try to allocate inode tables off
the end of the block group and fail, rather than warning that too
many inodes have been requested.

This is because when ext2fs_initialize calculates metadata overhead,
it is only adding in group descriptor blocks and the superblock
if the *last* bg contains them - but the first bg also has all of
the various metadata bits taking up space.

We need to calculate the overhead both for the first block group and
the last block groups separately, since the two different tests need
to know what the overheads are for those two cases, which may be
different.

*for example "mke2fs  -b 1024 -m 0 -g 256 -N 3745 fsfile 1024"

(Note, the test here is a little funky; the expected output is
actually a mkfs failure - but a proper failure instead of the
allocator catching the problem at the last minute)

Addresses-Red-Hat-Bugzilla: #241767

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
index 9cc3d12..16e9eaa 100644 (file)
--- a/lib/ext2fs/initialize.c
+++ b/lib/ext2fs/initialize.c
@@ -298,16 +298,13 @@ ipg_retry:
        }
 
        /*
-        * Overhead is the number of bookkeeping blocks per group.  It
-        * includes the superblock backup, the group descriptor
-        * backups, the inode bitmap, the block bitmap, and the inode
-        * table.
+        * Calculate the maximum number of bookkeeping blocks per
+        * group.  It includes the superblock, the block group
+        * descriptors, the block bitmap, the inode bitmap, the inode
+        * table, and the reserved gdt blocks.
         */
-
-       overhead = (int) (2 + fs->inode_blocks_per_group);
-
-       if (ext2fs_bg_has_super(fs, fs->group_desc_count - 1))
-               overhead += 1 + fs->desc_blocks + super->s_reserved_gdt_blocks;
+       overhead = (int) (3 + fs->inode_blocks_per_group +
+                         fs->desc_blocks + super->s_reserved_gdt_blocks);
 
        /* This can only happen if the user requested too many inodes */
        if (overhead > super->s_blocks_per_group)
@@ -316,8 +313,13 @@ ipg_retry:
        /*
         * See if the last group is big enough to support the
         * necessary data structures.  If not, we need to get rid of
-        * it.
+        * it.  We need to recalculate the overhead for the last block
+        * group, since it might or might not have a superblock
+        * backup.
         */
+       overhead = (int) (2 + fs->inode_blocks_per_group);
+       if (ext2fs_bg_has_super(fs, fs->group_desc_count - 1))
+               overhead += 1 + fs->desc_blocks + super->s_reserved_gdt_blocks;
        rem = ((super->s_blocks_count - super->s_first_data_block) %
               super->s_blocks_per_group);
        if ((fs->group_desc_count == 1) && rem && (rem < overhead))

diff --git a/tests/m_mkfs_overhead/expect.1 b/tests/m_mkfs_overhead/expect.1
new file mode 100644 (file)
index 0000000..fff3684
--- /dev/null
+++ b/tests/m_mkfs_overhead/expect.1
@@ -0,0 +1,10 @@
+./test.img: Cannot create filesystem with requested number of inodes while setting up superblock\r
+./test.img: Attempt to read block from filesystem resulted in short read while opening filesystem\r
+features: Filesystem not open\r
+ 
+../e2fsck/e2fsck: Attempt to read block from filesystem resulted in short read while trying to open ./test.img
+Could this be a zero-length partition?
+Exit status is 8
+
+../misc/dumpe2fs: Attempt to read block from filesystem resulted in short read while trying to open ./test.img\r
+Couldn't find valid filesystem superblock.

diff --git a/tests/m_mkfs_overhead/script b/tests/m_mkfs_overhead/script
new file mode 100644 (file)
index 0000000..8cd9134
--- /dev/null
+++ b/tests/m_mkfs_overhead/script
@@ -0,0 +1,5 @@
+DESCRIPTION="test bg overhead calculation"
+FS_SIZE=1024
+MKE2FS_OPTS="-b 1024 -m 0 -g 256 -N 3745"
+. $cmd_dir/run_mke2fs
+