In message <19990823152849.h83...@freebie.lemis.com>, Greg Lehey writes:

>> Why should it be made unavailable ?
>
>So that certain multiple accesses can be done atomically.

You don't need that.  You initialize a index to 0, and whenever
the sector with that index is written, you increment it.

At any one time you know that all parityblocks <= your index
are valid.

All you need to do to recover you index then is to have an
ioctl which will read one sector at a time, mark the buffer
dirty write it out again.

I have seen sources for two well-respected RAID-5 products
which do it this way.

>I'm a little surprised that there's any objection to the concept of
>mandatory locking.

Too many of us have had wedged systems because of it I guess...

--
Poul-Henning Kamp             FreeBSD coreteam member
p...@freebsd.org               "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!


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