an application to upon a tape (yea, even the non-control device) even if
it cannot establish a mount session. If the open cannot establish a mount
session and O_NONBLOCK was specified, the tape becomes 'open pending mount'.
All I/O operations that would require access to a tape thereafter until
a close attempt to initiate the mount session. If the mount session succeeds,
the tape driver transitions to full open state, else returns an appropriate
I/O error (ENXIO).
At the same time, add a change that remembers whether tape is being opened
read-only. If so, disallow 'write' operations like writing filemarks that
bypass the normal read-only filtering operations that happen in the write(2)
syscall.
Reviewed by: ken, justin, grog
MFC after: 2 weeks
Suggested by: The Bacula Team
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