Add support for LogFS Fillesystem

[shiren00]

We would appreciate it if anyone with additional materials or actual dump files related to this could share them :D

• https://en.wikipedia.org/wiki/LogFS
• https://web.archive.org/web/20100105200111/http://logfs.org/logfs/LogFS
• https://android.googlesource.com/kernel/msm/+/android-msm-marlin-3.18-nougat-dr1/fs/logfs/
• https://android.googlesource.com/kernel/msm/+/android-msm-marlin-3.18-nougat-dr1/fs/logfs/logfs_abi.h

[shiren00]

I'm not sure how to mount it, but since only mkfs.logfs was successful, I'm sharing it just in case.
logfs.zip

Apparently, 7a3a8e5cb9d5bf67 is the signature.

LogFS Header (https://android.googlesource.com/kernel/msm/+/android-msm-marlin-3.18-nougat-dr1/fs/logfs/logfs_abi.h)

/**
 * struct logfs_disk_super - on-medium superblock
 *
 * @ds_magic:			magic number, must equal LOGFS_MAGIC

struct logfs_disk_super {
	struct logfs_segment_header ds_sh;
	__be64	ds_magic;

/**
 * struct logfs_segment_header - per-segment header in the ostore
 *
 * @crc:			crc32 of header (there is no data)
 * @pad:			unused, must be 0
 * @type:			segment type, see above
 * @level:			GC level for all objects in this segment
 * @segno:			segment number
 * @ec:				erase count for this segment
 * @gec:			global erase count at time of writing
 */

struct logfs_segment_header {
	__be32	crc;
	__be16	pad;
	__u8	type;
	__u8	level;
	__be32	segno;
	__be32	ec;
	__be64	gec;
};

#define LOGFS_MAGIC		0x7a3a8e5cb9d5bf67ull /* =ds_magic */