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Re: GNU rm now works around Darwin 0.7.9 (MaxOS X 10.3.9) readdir bug

From: Jim Meyering
Subject: Re: GNU rm now works around Darwin 0.7.9 (MaxOS X 10.3.9) readdir bug
Date: Fri, 29 Sep 2006 17:06:16 +0200

Bruno Haible <address@hidden> wrote:

> Hi Jim,
> The Darwin HFS+ bug is even reproducible on Linux, on NFS mounts from a
> Darwin 10.3.9 machine. Here is that same directory, of which Darwin's
> readdir() bug occurred after 178 removals. Here it occurs already after
> 13 removals on average:
> $ ll charmaps | wc -l
> 195
> $ rm -r charmaps
> rm: cannot remove directory `charmaps': Directory not empty
> This means one has to enable the workaround with 8% speed penalty on all
> systems, not just Darwin...

Thanks for trying that.

I've been considering doing just that. Luckily, the 8% doesn't apply here,
since we needn't always do the rewind.  It's necessary only when rm has
removed enough files in a directory to provoke the bug.

That 8% was performing the rewind even when there was only
one entry in a directory, and with the very worst case
directory "shape", and on the very worst case type of file system
(tmpfs), where I/O overhead is very low, so normally insignificant
factors like that one would appear.

With the current choice of 10 (assuming rm imposes the cost for everyone)
that means for non-buggy systems, rm would perform an unnecessary rewind
upon end of dirstream only when it has removed 10 or more files from a
given directory.

In fact, I am unable to measure any significant performance difference.
I created a hierarchy of 30000 directories, each containing 11 files
on a tmpfs file system:

  seq --format=a/%g $n|xargs mkdir -p
  for i in $(seq $n); do seq --format=a/$i/%g 11;done|xargs touch

Then remove them all via "rm -rf a".
[The first has the work-around rewindir call, the second doesn't.]

  $ /usr/bin/time /cu/src/rm -rf a
  0.34user 3.45system 0:03.85elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+167minor)pagefaults 0swaps

  $ /usr/bin/time /p/bin/rm -rf a
  0.39user 3.37system 0:03.80elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+164minor)pagefaults 0swaps

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