Block Device Logger which writes and reads directly to or from a block device (e.g. USB-memory) without using a filesystem. It can also use a fixed size file. BDL tries to minimize the strain on individual parts of a device by using the whole device in a round-robin fashion, with metadata to aid searcing spread around at fixed points.
A BDL structure consist of a header at the start of the device which is only written to when first initializing the device. Fixed size blocks of data are then written after this header. A region consists of many blocks (usually 128MB) before ending with a hint block which contains information about where to find the most recent block before it. The hint blocks and other blocks are not pre- initialized, and BDL merely considers any block with invalid checksum to be free space.
Backup hint blocks are placed half way inside each region. If a hintblock is corrupt, we attempt to recover the backup.
The data blocks have a timestamp and a user defined identifier. When writing a new entry, BDL searches the hint blocks to find unused space. If the device was full, the oldest data block is overwritten, and the rest of this region is also invalidated. The hint blocks are always updated on writes. Timestamp of new entries must be larger than all exisiting entries.
To initialize a device, the user must first overwrite the start of it with zeros. This is to prevent accidental overwrites of filesystems. It is possible to choose which block size to use, and data written has to be less than the block size minus the block header size.
Only the master header is written at initialization, the rest of the structure is created dynamically on data writes. If an existing structure is present on a device, it can be used if the block size happen to match the new blocksize. To prevent this, the hint blocks has to be overwritten.
All blocks are checksummed with CRC32. If the master header is corrupted, no operations may be performed. If a hint block or data block is corrupted, it is considered free space.
Initializes a device by writing a new header.
dev Device or file to initialize
May specify @SIZE to reduce the space actually used
bs The fixed size of blocks and hint blocks,
must be dividable by 256
hpad The size of the master header, can be used to change the
position of hint blocks if desirable.
padchar The character to use for padding blocks in hex, defaults to 0xff.
Correct value may relieve strain on some memory chips.Write a new data block to the next free location or overwrite oldest entry.
appdata Save application-specific data ignored by BDL. Default is 0.
timestamp Set a timestamp manually in microseconds. Default is current time.
faketimestamp If the timestamp is equal to the last entry, increment it by 1
up to NUM times. Error occurs when NUM is exceeded.Read blocks and print to STDOUT.
ts_gteq Specifiy a minimum timestamp of blocks to print. Default is 0.
limit Stop after this many entries are found. 0 means no limit (default).Opens an interactive session. Device specified is kept open until "close" is called. Commands which require dev={DEVICE} now uses the open device instead, and attempts to specify it will fail the program.
Clear all hint blocks