Bug or Feature? -- Disappearing /dev/ nodes after mount

[Polytropon]

On Thu, 11 Jun 2020 23:54:55 -0700, David Christensen wrote:
> On 2020-06-11 23:22, Polytropon wrote:
> > On Thu, 11 Jun 2020 16:14:09 -0700, Ronald F. Guilmette wrote:
> 
> >> Interestingly, as I have just learned, when and if the user subesquently
> >> mounts the relevant partition, the corresponding `/dev/gpt/partname' node
> >> will, rather unexpectedly and magically, disappear until such time as the
> >> relevant partition is unmounted, whereupon it will reappear.
> 
> >> 1)  Is this behavior documented somewhere that I just failed to look at?
> >> If so, where?
> > 
> > Interesting question - I would be interested in that, too.
> 
> See Lucas, AF3E, p. 214 "GEOM Withering" [1].

Wow, thanks for providing the term. techn. "GEOM Withering",
which leads to usable search results, for example:

	This GEOM names appearing and disappearing is the
	consequence of *GEOM withering. A GEOM can be used
	in three different ways: 
		- reading
		- writing
		- with exclusive access
	The latter is the cause of GEOM withering: once a
	disk is mounted an exclusive lock is required to
	inform the other available GEOM providers that the
	disk is in-use. GEOM therefore withers the other
	disk available names, that results in the names to
	disappear from the dev filesystem. For more
	information see g_wither_geom(9) and geom(4)
	ORPHANIZATION example.

Source:

https://fluca1978.github.io/2017/10/05/FreeBSD-Wither.html

And from that point, local documentation at "man 4 geom" says:

	ORPHANIZATION is the process by which a provider
	is removed while it potentially is still being used.

	[...]

	When a provider is orphaned, this does not necessarily
	result in any immediate change in the topology: any
	attached consumers are	still attached, any opened
	paths are still	open, any outstanding I/O requests are
	still outstanding.

with an explanation of what happens, with additional info
found in "man 9 g_wither_geom".

Today I learned. ;-)


-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...