ext2fs: cache the superblock

Previously, the superblock was mmaped and a pointer stored in sblock
by map_hypermetadata.  This memory is backed by our disk pager.

This is rather unfortunate, as this means that whenever we read a
value from that location, we might generate a request our disk pager.
This amplifies the so-called thread-storm problem.

Rather than relying on a mmaped region of memory, just use the data
loaded by get_hypermetadata.

* ext2fs/hyper.c (get_hypermetadata): Do not free sblock.
(mapped_sblock): New variable.
(map_hypermetadata): Map the superblock to mapped_sblock instead.
(diskfs_set_hypermetadata): Copy superblock into mapped_superblock.
* ext2fs/ext2fs.h (get_hypermetadata, map_hypermetadata): Adjust
comments accordingly.

0 files changed, 0 insertions, 0 deletions