NAME
        LockDosList -- Locks the specified Dos Lists for use (V36)

   SYNOPSIS
        dlist = LockDosList(flags)
        D0                   D1

        struct doslist *lockdoslist(ulong)

   FUNCTION
        Locks the dos device list in preparation to walk the list.
        If the list is 'busy' then this routine will not return until it is
        available.  This routine "nests": you can call it multiple times, and
        then must unlock it the same number of times.  The dlist
        returned is NOT a valid entry: it is a special value.  Note that
        for 1.3 compatibility, it also does a forbid() - this will probably
        be removed at some future time.  The 1.3 forbid() locking of this
        list had some race conditions.  The pointer returned by this is NOT
        an actual doslist pointer - you should use on of the other dosentry
        calls to get actual pointers to doslist structures (such as
        nextdosentry()), passing the value returned by lockdoslist()
        as the dlist value.

        Note for handler writers: you should never call this function with
        LDF_WRITE, since it can deadlock you (if someone has it read-locked
        and they're trying to send you a packet).  Use attemptlockdoslist()
        instead, and effectively busy-wait with delays for the list to be
        available.  The other option is that you can spawn a process to
        add the entry safely.

        As an example, here's how you can search for all volumes of a specific
        name and do something with them:

        2.0 way:

                dl = LockDosList(LDF_VOLUMES|LDF_READ);
                while (dl = FindDosEntry(dl,name,LDF_VOLUMES))
                {
                        Add to list of volumes to process or break out of
                        the while loop.
                        (You could try using it here, but I advise
                        against it for compatability reasons if you
                        are planning on continuing to examine the list.)
                }

                process list of volumes saved above, or current entry if
                you're only interested in the first one of that name.

                UnLockDosList(LDF_VOLUMES|LDF_READ);
                                  * must not use dl after this! *

        1.3/2.0 way:

                if (version >= 36)
                        dl = LockDosList(LDF_VOLUMES|LDF_READ);
                else {
                        Forbid();
                        /* tricky! note dol_Next is at offset 0! */
                        dl = &(...->di_DeviceList);
                }

                while (version >= 36 ?
                                dl = FindDosEntry(dl,name,LDF_VOLUMES) :
                                dl = yourfindentry(dl,name,DLT_VOLUME))
                {
                        Add to list of volumes to process, or break out of
                        the while loop.
                        Do NOT lock foo1/foo2 here if you will continue
                        to examine the list - it breaks the forbid
                        and the list may change on you.
                }

                process list of volumes saved above, or current entry if
                you're only interested in the first one of that name.

                if (version >= 36)
                        UnLockDosList(LDF_VOLUMES|LDF_READ);
                else
                        Permit();
                * must not use dl after this! *
                ...

                struct doslist *
                yourfindentry (struct doslist *dl, strptrname, type)
                {
                * tricky - depends on dol_Next being at offset 0,
                   and the initial ptr being a ptr to di_DeviceList! *
                        while (dl = dl->dol_Next)
                        {
                            if (dl->dol_Type == type &&
                                stricmp(name,BADDR(dl->dol_Name)+1) == 0)
                            {
                                break;
                            }
                        }
                        return dl;
                }

   INPUTS
        flags - Flags stating which types of nodes you want to lock.

   RESULT
        dlist - Pointer to the head of the list.  NOT a valid node!

   SEE ALSO
        attemptlockdoslist(), unlockdoslist(), forbid(), nextdosentry()