[B2-devel] Leggo my Eggo! (The CD-ROM eject fix)

[Robert M. <mr...@gm...>]

This affects both BasiliskII and SheepShaver, on Mac OS X host
systems, when the "nocdrom" setting is set to "true".

I keep lots of old files archived on CD-ROMs, and I often use these
CD-ROMs while BasiliskII or SheepShaver is running. The CD-ROMs are
for MacOS X, they wouldn't work in the emulator even if I tried, so I
have "nocdrom true" in both my .basilisk_ii_prefs and
.sheepshaver_prefs files.

There has been a bug for many years that causes this setting to only
partly work. "nocdrom true" prevents the emulator from emulating the
CD-ROM, but if you insert a disc after launching the emulator, it
still grabs onto the CD-ROM as if it were being used, and it never
lets go. If you want to eject the CD-ROM, the Finder removes the icon
from the desktop but it doesn't eject. Disk Utility tells you it can't
be unmounted. You have to quit BasiliskII or SheepShaver before
ejecting it.

A little searching through the source code turns up the routine
"SysMediaArrived", which is defined in sys_unix.cpp and invoked from
sys_darwin.cpp. As you can see, it does perform an appropriate test:

  if (type == MEDIA_CD && !PrefsFindBool("nocdrom"))

but this test only affects whether or not it does the following
"PrefsReplaceString("cdrom", path);" step.

The rest of the actions, including in particular the call to
"cdrom_open(fh, path)", are performed regardless of the "nocdrom"
setting.

This makes it open the CD-ROM device (such as "/dev/disk1" on one of
the systems I tested) which is why the disc cannot be ejected.
Unfortunately, there is no way to get it to close the device later.
Because CD-ROM is turned off, the disc never appears inside the
emulated MacOS, and so there is no way to ask the emulated Mac to
eject it.

The fix I decided to try is relatively simple. If "nocdrom" is true,
the entire SysMediaArrived routine is superfluous. So I added a test
at the very beginning of SysMediaArrived that exits:

    if ((type == MEDIA_CD) && PrefsFindBool("nocdrom")) {
        // Do nothing
        return;
    }

With this change I am able to insert and eject as many CD-ROMs as I
want while SheepShaver is running, without having to make SheepShaver
quit.

There are probably other ways to fix this. SysMediaArrived is called
from media_arrived in sys_darwin.cpp, and media_arrived is installed
by a call to IOServiceAddMatchingNotification. I suspect that one
could put a test of PrefsFindBool("nocdrom") somewhere in here to
prevent installing the notification handler in the first place. But I
don't know what else that might affect (there might be other media
that can arrive apart from CDROMs).

Also, the presence of the incorrect code in sys_unix.cpp makes it look
like this bug might also affect Linux users.

Comments welcome...

-- 
  Robert Munafo  --  mrob.com
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