lost free blocks on the UNIX PC

[David Solan]

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Last November John Chambers commented that there is an
"out-of-free-blocks" bug in UNIX for the UNIX PC (I also believe
this problem exists for other versions of System V UNIX on other
machines).  I am posting this to offer my full agreement.  The
problem can even occur in SINGLE-user mode!

If you allocate and write to many files (a 100 or more) in rapid
succession, such as within a C program in the space of a second or
less, AND then immediately unlink and remove all these files very
rapidly, AND then immediately reallocate and write to another 100
files or so very rapidly, AND then immediately unlink and remove
this second batch of files very rapidly, UNIX -- sometimes (NOT
ALWAYS!) -- will cough.  In the second mass file deletion, the
files will indeed be removed, but sometimes their data blocks will
not, I repeat *NOT*, be put on the free block list of UNIX.  I can
assure you, this is true.  Considering this happens in single-user
mode, this is clearly a bug in UNIX's file allocation/removal
algorithms, and has nothing to do with multi-user race conditions.

Upon the next running of fsck, the orphaned blocks are put back on
the free block list.  And the problem can be obviated entirely by
running lots of sync's and sleep's between the removals and
reallocations.

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David  Solan
Objective Programming Incorporated
Post Office Box 123
Norwalk,  CT  06856
Voice: (203) 866-6900
attmail: !dsolan
USENET: gizzmo!kdavid
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                                             {codas,u1100a}-----\
David Solan                         rutgers!rochester!pcid!kodak!gizzmo!kdavid
                                       {lazlo,ethos,fthood}-----/