- Change falloc() to acquire an fd from the process table last so that   it can do it w/o needing to hold the filelist_lock sx lock. - fdalloc() doesn't need Giant to call free() anymore.  It also doesn't   need to drop and reacquire the filedesc lock around free() now as a   result. - Try to make the code that copies fd tables when extending the fd table in   fdalloc() a bit more readable by performing assignments in separate   statements.  This is still a bit ugly though. - Use max() instead of an if statement so to figure out the starting point   in the search-for-a-free-fd loop in fdalloc() so it reads better next to   the min() in the previous line. - Don't grow nfiles in steps up to the size needed if we dup2() to some   really large number.  Go ahead and double 'nfiles' in a loop prior   to doing the malloc(). - malloc() doesn't need Giant now. - Use malloc() and free() instead of MALLOC() and FREE() in fdalloc(). - Check to see if the size we are going to grow to is too big, not if the   current size of the fd table is too big in the loop in fdalloc().  This   means if we are out of space or if dup2() requests too high of a fd,   then we will return an error before we go off and try to allocate some   huge table and copy the existing table into it. - Move all of the logic for dup'ing a file descriptor into do_dup() instead   of putting some of it in do_dup() and duplicating other parts in four   different places.  This makes dup(), dup2(), and fcntl(F_DUPFD) basically   wrappers of do_dup now.  fcntl() still has an extra check since it uses   a different error return value in one case then the other functions. - Add a KASSERT() for an assertion that may not always be true where the   fdcheckstd() function assumes that falloc() returns the fd requested and   not some other fd.  I think that the assertion is always true because we   are always single-threaded when we get to this point, but if one was   using rfork() and another process sharing the fd table were playing with   the fd table, there might could be a problem. - To handle the problem of a file descriptor we are dup()'ing being closed   out from under us in dup() in general, do_dup() now obtains a reference   on the file in question before calling fdalloc().  If after the call to   fdalloc() the file for the fd we are dup'ing is a different file, then   we drop our reference on the original file and return EBADF.  This   race was only handled in the dup2() case before and would just retry   the operation.  The error return allows the user to know they are being   stupid since they have a locking bug in their app instead of dup'ing   some other descriptor and returning it to them.
- Change falloc() to acquire an fd from the process table last so that
  it can do it w/o needing to hold the filelist_lock sx lock.
- fdalloc() doesn't need Giant to call free() anymore.  It also doesn't
  need to drop and reacquire the filedesc lock around free() now as a
  result.
- Try to make the code that copies fd tables when extending the fd table in
  fdalloc() a bit more readable by performing assignments in separate
  statements.  This is still a bit ugly though.
- Use max() instead of an if statement so to figure out the starting point
  in the search-for-a-free-fd loop in fdalloc() so it reads better next to
  the min() in the previous line.
- Don't grow nfiles in steps up to the size needed if we dup2() to some
  really large number.  Go ahead and double 'nfiles' in a loop prior
  to doing the malloc().
- malloc() doesn't need Giant now.
- Use malloc() and free() instead of MALLOC() and FREE() in fdalloc().
- Check to see if the size we are going to grow to is too big, not if the
  current size of the fd table is too big in the loop in fdalloc().  This
  means if we are out of space or if dup2() requests too high of a fd,
  then we will return an error before we go off and try to allocate some
  huge table and copy the existing table into it.
- Move all of the logic for dup'ing a file descriptor into do_dup() instead
  of putting some of it in do_dup() and duplicating other parts in four
  different places.  This makes dup(), dup2(), and fcntl(F_DUPFD) basically
  wrappers of do_dup now.  fcntl() still has an extra check since it uses
  a different error return value in one case then the other functions.
- Add a KASSERT() for an assertion that may not always be true where the
  fdcheckstd() function assumes that falloc() returns the fd requested and
  not some other fd.  I think that the assertion is always true because we
  are always single-threaded when we get to this point, but if one was
  using rfork() and another process sharing the fd table were playing with
  the fd table, there might could be a problem.
- To handle the problem of a file descriptor we are dup()'ing being closed
  out from under us in dup() in general, do_dup() now obtains a reference
  on the file in question before calling fdalloc().  If after the call to
  fdalloc() the file for the fd we are dup'ing is a different file, then
  we drop our reference on the original file and return EBADF.  This
  race was only handled in the dup2() case before and would just retry
  the operation.  The error return allows the user to know they are being
  stupid since they have a locking bug in their app instead of dup'ing
  some other descriptor and returning it to them.

Tested on:	i386, alpha, sparc64

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase