The Ftape Installation Guide - File marks
This was Bas Laarhoven's original comment in the file `ftape-eof.c
'
of the ftape-2.x distribution. zftape doesn't use this technique anymore; Bas'
comment is included for reference only.
Note that the sftape module has vanished from the ftape-3.x distribution since version 3.04. This section is here merely to explain the differences between ftape-2.x and ftape-3.04d
Ftape (mis-)uses the bad sector log to record end-of-file marks. Initially (when the tape is erased) all entries in the bad sector log are added to the tape's bad sector map. The bad sector log then is cleared.
The bad sector log normally contains entries of the form: even 16-bit word: segment number of bad sector odd 16-bit word: encoded date There can be a total of 448 entries (1792 bytes).
my guess is that no program is using this bad sector log (the format seems useless as there is no indication of the bad sector itself, only the segment) However, if any program does use the bad sector log, the format used by ftape-2.x will let the program think there are some bad sectors and no harm is done.
The eof mark entries that ftape-2.x stores in the bad sector log: even 16-bit word: segment number of eof mark odd 16-bit word: sector number of eof mark [1..32]
The eof_map as maintained is a sorted list of eof mark entries.
The tape name field in the header segments is used to store a Linux tape identification string and a version number. This way the tape can be recognized as a Linux raw format tape when using tools under other OS's.
'Wide' QIC tapes (format code 4) don't have a failed sector list anymore. That space is used for the (longer) bad sector map that now is a variable length list too. We now store our end-of-file marker list after the bad-sector-map on tape. The list is delimited by a (__u32) 0 entry.
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