LogFS take four

[Jörn Engel]

This round the patch is split into file-sized hunks.  There actually
seem to be kernel developers not manly enough to digest 6000+ lines of
code at once.  An I thought I was the only wimp around.

Again, anyone giving comments in the last round is on Cc:.

I'll try to respond to comments but the next round of patches may take a
while longer, due to other responsibilities.


Changed since take three:
o one blank line between functions
o depend on MTD
o use LOGFS_BLOCKSHIFT in logfs_index
o #define EOF to 512
o moved BUILD_BUG_ON() into an inline function
o declare completion futility on the stack
o 64bit nanoseconds time format
o created logfs_compare_inode()
o created struct logfs_device_ops
o truncate() to zero sets embedded flag
o unwrap logfs_memcpy()
o add FS_READONLY flag to superblock
o create blockdev_device_ops
  This one still needs some infrastructure and testing.
o Fix data corruption bug.


Unchanged:
o convert #define's to enums.
  Afaics one of those has to be cast to u8, the other has to go through
  cpu_to_be64.  I don't see how enums are an advantage under such circumstances
  and Thomas didn't seem to be sure either.
o generic function for logfs_type()
o generic helper for logfs_prepare_write()
o removed EOF
o error handling
o move rootdir generation back to mkfs
o replace kmap() with kmap_atomic()
o document logfs_new_meta_inode()
o Use KMEM_CACHE() helper for kmem_cache_create()
o read object header first, then read or read&uncompress object data
o shrink inodes to 200 bytes


Won't happen (unless I get convinced to do otherwise):
o lowercase LOGFS_SUPER and LOGFS_INODE
  These simply match the common pattern used is many Linux filesystems.
o remove "extern"
  For structures, this keyword actually serves a purpose and makes sense.
  On the other hand, it is completely bogus for functions and I won't be
  bullied into adding bogus crud either.
o Move fs/logfs/Locking to Documentation/
  At least JFFS2 has such documentation in its own directory as well.
  I can see good arguments for either side and no strong consensus.  While
  I ultimately just don't case, doing nothing is a good option in cases
  of great uncertainty.
o change (void*) to "proper" cast
  Neither variant is much better than the other.  I'm open for suggestions
  to completely remove the casts, though.
o Change LOGFS_BUG() and LOGFS_BUG_ON() to inline functions
  These are macros for very much the same reasons BUG() and BUG_ON() are.

Jörn

-- 
A victorious army first wins and then seeks battle.
-- Sun Tzu