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
5fc3031366