From: utzoo!decvax!ucbvax!C70:info-cpm Newsgroups: fa.info-cpm Title: Deblocking Article-I.D.: ucb.1590 Posted: Sat Jul 24 17:22:57 1982 Received: Tue Jul 27 02:02:16 1982 >From JWP@Mit-Mc Sat Jul 24 17:22:45 1982 A while ago I tried to send a message to INFO-CPM but was having some problems getting it out. What follows is that message. My appolgies to those who may be getting this for the second time. ================ Up until recently, I had taken the deblocking algorithm for granted while doing some extensive (commercial) work with the BIOS/monitor for my SuperBrain. Without much thought and a few patches, I just inserted the DR supplied code. With all this talk of problems with the code lately, I decided that I should sit down and really look at what it does. I was especially interested because of a problem sometimes encountered while doing a wildcard file transfer in PIP where it would lose its place in the directory and end up skipping half the files. Checking for a patch in the BDOS, the lack of which might cause such a condition, I found that the patch had been implemented and so my illusive gremlin was still at large (and remains so today). I finally was able to comprehend how the blocking/deblocking algorithm worked and found nothing out of order except that in the 2.0 release of the algorithm, DR neglected to clear UNACNT in READ. One thing that gets me is that while the read algoritms are good and serve their purpose well, it seems that the write logic is a little lacking. Would it be proper thinking to write only when necessary (ie. the way reads are done)? Of course, the directory write can be used to force a write. This approach seems reasonable enough. The only time data would be lost is when either a cold boot is performed or the system goes down before the current buffer is written. When you think about it, entire extents are usually lost when this happens anyway - the unwritten buffer wouldn't be missed unless you know how to use DU to rebuild the extent. Files would be closed with the forced (directory) write function (1). Jonathan Platt@MIT-MC ================ Since then, I have found the problem with PIP. It was hardware. Any thoughts on the write-only-when-necessary philosophy?