Re: swapon vs GEOM labels

On Mon, Oct 21, 2024 at 3:40 AM Stephane Rochoy <
stephane.rochoy@stormshield.eu> wrote:

> Hi Hackers,
>
> I'm playing with glabel(8) and swapon(8) but found a behavior that
> is somewhat puzzling.
>
> I boot main (b88df1e893c4) with an USB memstick plugged. The
> memstick is da0 and hold a freebsd-swap partition, da0p1. This
> partition was given the `swap` label using `glabel label` (i.e.,
> an automatic label, stored somewhere into da0p1, AFAIK).
>
>   # glabel status
>         Name  Status  Components
>   label/swap     N/A  da0p1
>
> Then I give the whole device the `usbmemstick` label using `glabel
> create` (i.e., a manual label, not stored anywhere).
>
>   # glabel create usbmemstick da0
>   # glabel status
>               Name  Status  Components
>         label/swap     N/A  da0p1
>   label/usbmemstick    N/A  da0
>
> What puzzle me is what happen when I enable swap:
>
>   # sysctl vm.nswapdev
>   vm.nswapdev: 0
>   # swapctl -l
>   Device:      1024-blocks     Used:
>   # dumpon -l
>   /dev/null
>   # swapon /dev/label/usbmemstickp1
>   # glabel status
>               Name  Status  Components
>   label/usbmemstick    N/A  da0
>   # swapoff /dev/label/usbmemstickp1
>   # glabel status
>               Name  Status  Components
>   label/usbmemstick    N/A  da0
>         label/swap     N/A  label/usbmemstickp1
>
> While swap is enabled, the `swap` label is no longer available. It
> comes back when swap is disabled.
>
> Note that I also tried to enable swap using the automatic label
> (i.e., `swap`). In such a case this is the `usbmemstick` label
> that vanish. And the label is even not restored on `swapoff`.
>
> Is it the expected behavior? Am I doing something wrong?
>

This both makes sense to me, and seems wrong to me.  When
things are nested like this, it kinda makes sense that label/usbmemstickp1
shows up. geom doesn't enumerate everything and this seems to be a bit
of an artifact. I'd expect both label/usbmemstickp1 and label/swap to be
there.
geom does odd things with devices that are open to keep others from opening
them, and this may just be an artifact of this kinda weird behavior.

Warner