Re: Expected getdents behaviour

[tridge@samba.org]

At the risk of thowing a spanner in the works, Samba relies pretty
heavily on seekdir()/telldir()/unlink() interacting in "nice"
ways. 

The most problematic case is OS/2 clients, which use a bizarre pattern
for removing all files in a directory. I've coded up the equivalent
set of posix directory operations for a OS/2 client deleting a
directory in:

  http://samba.org/ftp/unpacked/junkcode/os2_delete.c

what they do is:

 1) open directory
 2) read 100 entries, asking for the 'telldir' location of each
 3) delete the first 4 of those entries
 4) seekdir to the offset returned by the 4th entry (now deleted)
 5) read another 100 entries
 6) go to step 3

this continues until the read of the directory returns no entries. At
this point the client assumes the directory is empty.

This works fine on Linux. On FreeBSD systems the way libc telldir()
works means that the above pattern uses a huge amount of memory, and
ends up not deleting all entries in the directory, so we ended up
replacing telldir() on FreeBSD inside Samba4. See:

  http://samba.org/ftp/unpacked/samba4/source/lib/replace/repdir/

So if this discussion leads to any changes in getdents(), please don't
use the FreeBSD method (it allocates a linked list of all telldir()
results, and doesn't correctly cope with deletions during a directory
scan). 

Cheers, Tridge