Bizarre clone attempt failures on Raspberry Pi2...

[Karl Denninger]

On 7/15/2016 09:22, Paul Mather wrote:

> On Jul 15, 2016, at 9:44 AM, Karl Denninger <karl at denninger.net> wrote:
>
>> On 7/15/2016 08:36, Paul Mather wrote:
>>> On Jul 14, 2016, at 11:36 PM, Karl Denninger <karl at denninger.net> wrote:
>>>
>>>> Found it.
>>>>
>>>> Apparently the current code *requires* the label be set on the msdos
>>>> partition.  If it's not then not only does it not mount (which shouldn't
>>>> matter post-boot as the loader is supposed to pass the dtb file, it is
>>>> specified in the config file without any sort of path prefix, and thus
>>>> once the kernel has loaded it should not matter if the dos partition if
>>>> actually mounted or not) *but* the boot process hangs without any
>>>> indication of why!
>>>>
>>>> So, you must do newfs_msdos -L MSDOSBOOT -F 16 {device}
>>>>
>>>> If the "-L" is missing you're hosed; the system facially appears to be
>>>> just fine but while the loader comes up and so does the kernel, it hangs
>>>> without ever proceeding -- and without any sort of error message
>>>> indicating that it is unable to mount something it needs.
>>> You have to do that because the device entry in the stock /etc/fstab is /dev/msdosfs/MSDOSBOOT.  The /dev/msdosfs part indicates it's using ms-dos labels.  In other words, this is just the same sort of failure you were getting when you weren't labelling the UFS partition as "rootfs".  Labelling the file system properly "fixes" the issue, as you would expect.
>>>
>>> It's a misnomer to say the code "requires" labels.  It's just that's the way the distribution images are currently set up.  I have an older Pi that predates the current distribution images that just uses /dev/mmcsd0... device names in /etc/fstab.  Both approaches work fine.  You just need to make sure the devices you specify in /etc/fstab will actually exist when it comes time to mount the corresponding file system.
>> Except that if the root filesystem doesn't mount you get an error, and
>> thus you can figure out what's going on.  What excuse is there for not
>> printing an error message if a mount fails, and if something in
>> /etc/fstab fails to mount what's with hanging the machine?  I've had
>> disks be unavailable before on Intel architecture machines (it happens
>> when disks fail) and the result is an error on the failure to mount but,
>> unless it's the root volume, the system still comes up.
>
> Are you sure you don't get an error?  When I forgot to label rootfs recently when I cloned an SD card I got an error displayed on the serial console.  I didn't get an error on the HDMI screen console.
You get an error if rootfs is not labelled on the HDMI screen (as root
fails to mount.) There is *no* error on an HDMI screen if the msdosfs is
not labeled.
> As I've mentioned before directly, FreeBSD/arm acts like console="comconsole,vidconsole" is in effect.  This means that during /etc/rc boot processing, you'll only get output on comconsole (except for kernel messages, which seem to go to both).  That's been my experience in FreeBSD in general.
>
> I dimly recall folks on here saying U-Boot doesn't currently enable/support USB keyboards, so there's not really much you can do to fix it interactively if you fail to boot the OS and hence enable USB keyboard support via FreeBSD.  That's not a problem if you use a serial console, which is supported by U-Boot.
Well, that's not true if the kernel is loaded.  Once the kernel loads a
usb keyboard works.
>
> I'm not sure comparisons with Intel architecture machines is entirely appropriate as they use a different boot environment/mechanism.  Still, I stand by the fact that I've always got an error message on the serial console when disks on my FreeBSD/arm system have failed to mount at boot.  (It used to happen regularly with an external USB drive I had that took a long time to probe, and I ended up having to put a kern.cam.boot_delay in /boot/loader.conf to avoid the system dropping into single-user mode when doing a reboot.)
>
>
>>> If you stop using labels in your /etc/fstab then you won't have problems when those labels are missing.  If the labels are missing, the /dev/{msdosfs,ufs} devices will not be present and the system will drop to single-user mode because none-late, non-noauto file systems can't be accessed via their device nodes when attempting to mount them.  When that happens and you don't have a serial console enabled then you have problems remediating the situation.
>>>
>>> If a file system is not needed to mount as part of booting (as you suggest for /boot/msdos) then you should probably flag it with the "noauto" option in /etc/fstab or remove it from /etc/fstab entirely.
>>>
>>> I think the problem you were having is not copying all the required attributes of the file systems in question when cloning your SD cards, given your /etc/fstab setup.  It sounds like you've fixed that, now.
>> Again, if it dropped to single user mode *and said it was doing so* or
>> if there was an error message on the console when the filesystem failed
>> to mount I would have found this in a reasonable period of time.  It
>> wasn't that rough to do so with the ufs label once I knew the filesystem
>> was failing to mount, which was discernible from the console output.
>>
>> Not printing an error when things error out is rude at best, and when
>> that error is going to prevent the system from coming up this darn well
>> ought to show up where one with a monitor plugged in can see it, eh?
>>
>> There was literally no indication at all as to what was going on and
>> since gpart does not show filesystem labels for *either* BSD labeled
>> slices OR msdos figuring out what was different between the two proved
>> to be a bit troublesome.  IMHO at least the failure to display an error
>> message in this circumstance ought to be corrected.
>
> See above re: serial console vs. video console.
>
> As for the labels, these are file system labels and not partition labels.  The big clue is in the device name in /etc/fstab.  (The "-l" option to "gpart show" will only show labels "[f]or partitioning schemes that support partition labels".  That's reasonable, IMHO, as partitions are not the same as file systems and gpart is concerned with partitions.)  In my experience, complaints about not being able to access /dev/ufs/something means you forgot to label a UFS file system as "something" when you made it. :-)
>
> Cheers,
>
> Paul.

Understood, but the issue here is that there's no indication without a
serial console that you have anything wrong -- the system appears to
have simply hung.

The quick fix is to put "failok" (or noauto) in the default /etc/fstab
entry for the dos filesystem, since it is not necessary for that
filesystem to be mounted at all on a running machine.  If there is a
policy reason to leave it accessible (and there's a fairly-clean
argument that there is) then "failok" might be preferable to "noauto",
but either way forcing a filesystem that is not necessary to be
accessible or the system fails to come up and does not give any
indication of same on what many users will have accessible to them is
facially wrong.

These devices are thought of as "appliances" by many and as such the
model of USB keyboard + HDMI (e.g. TV or monitor) is entirely
reasonable, and IMHO FreeBSD ought to, when possible, make that a viable
option.  It both is and can be provided the kernel loads, but the
defaults in pre-built configurations right now preclude that.

-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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