Re: Vanishing GPT/UFS labels

On 5/21/26 23:53, Stéphane Rochoy wrote:
> Warner Losh <[email protected]> writes:
> 
>> On Thu, May 21, 2026 at 6:46 AM Stéphane Rochoy <[email protected]> wrote:
>>  …
>>  When I mount using the underlying device, /dev/${md}p2, both
>>  /dev/gpt/bar and /dev/ufs/bar vanish. And when I umount (using the mount
>>  point) both are back.
>>
>>  When I mount using the UFS label, /dev/ufs/bar, only /dev/gpt/bar
>>  vanish. And when I umount the GPT label don't come back.
>>
>>  GEOM don't seems to agree with itself: `gpart show -l $md` do confirm both
>>  partitions kept their GPT label but `glabel status` don't:
>>
>>      $ gpart show -l $md
>>      =>    40  204720  md0  GPT  (100M)
>>            40   20480    1  foo  (10M)
>>         20520  184240    2  bar  (90M)
>>      $ glabel status | grep -e foo -e bar
>>           gpt/foo     N/A  md0p1
>>           ufs/bar     N/A  md0p2
>>
>>  I would be happy to hunt what looks like bugs to me but I need some
>>  insight first: what is the rationale behind the idea to remove a device
>>  on mount and, possibly, restore it on umount?
>>
>> This sounds like the intentional behavior of geom to withdraw the
>> devices when aliases are mounted.
> 
> So what I observe when mounting/umounting via the underlying device
> (/dev/${md}p2) is the expected behavior.
> 
> But there's some problems when mounting/umounting via the UFS label
> (/dev/ufs/bar):
> - on mount, /dev/ufs/bar should vanish too

Are you saying that the mounted /dev/ufs/bar that shows up in df -m
should instead show up via under a path one did not specify, such as a
/dev/mdp2 ?

My example below is a gpt mount context instead of ufs, just because
that is what I happen to have around:

# gpart show -pl /dev/da0
=>        34  2930277101    da0  GPT  (1.4T)
          34       32734         - free -  (16M)
       32768      501760  da0p1  PBaseEFI  (245M)
      534528    20971520  da0p2  PBaseSwp10  (10G)
    21506048    29360128  da0p3  PBaseSwp14  (14G)
    50866176    33554432  da0p4  PBaseSwp16  (16G)
    84420608    67108864  da0p5  PBaseSwp32  (32G)
   151529472    96468992  da0p6  PBaseSwp46  (46G)
   247998464   268435456  da0p7  PBaseSwp128  (128G)
   516433920     7340032  da0p8  PBaseSwp3p5  (3.5G)
   523773952    13096960         - free -  (6.2G)
   536870912  2357198848  da0p9  PBaseUFS  (1.1T)
  2894069760    36207375         - free -  (17G)

# gpart show -p /dev/da0
=>        34  2930277101    da0  GPT  (1.4T)
          34       32734         - free -  (16M)
       32768      501760  da0p1  efi  (245M)
      534528    20971520  da0p2  freebsd-swap  (10G)
    21506048    29360128  da0p3  freebsd-swap  (14G)
    50866176    33554432  da0p4  freebsd-swap  (16G)
    84420608    67108864  da0p5  freebsd-swap  (32G)
   151529472    96468992  da0p6  freebsd-swap  (46G)
   247998464   268435456  da0p7  freebsd-swap  (128G)
   516433920     7340032  da0p8  freebsd-swap  (3.5G)
   523773952    13096960         - free -  (6.2G)
   536870912  2357198848  da0p9  freebsd-ufs  (1.1T)
  2894069760    36207375         - free -  (17G)

# cat /etc/fstab
/dev/gpt/PBaseUFS		/		ufs	rw,noatime		1	1
/dev/gpt/PBaseEFI		/boot/efi	msdosfs	rw,noatime		0	0
/dev/gpt/PBaseSwp3p5		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp10		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp14		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp16		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp32		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp46		none		swap	sw,noauto		0	0
/dev/gpt/PBaseSwp128		none		swap	sw,noauto		0	0

# ls -C1dF /dev/gpt/*
/dev/gpt/PBaseEFI
/dev/gpt/PBaseSwp10
/dev/gpt/PBaseSwp128
/dev/gpt/PBaseSwp14
/dev/gpt/PBaseSwp16
/dev/gpt/PBaseSwp32
/dev/gpt/PBaseSwp3p5
/dev/gpt/PBaseSwp46
/dev/gpt/PBaseUFS

(Note that they are not symbolic links to /dev/da0p* examples.)

# df -m
Filesystem        1M-blocks   Used  Avail Capacity  Mounted on
/dev/gpt/PBaseUFS   1114846 219903 805754    21%    /
devfs                     0      0      0     0%    /dev
/dev/gpt/PBaseEFI       244     27    217    11%    /boot/efi

The system uses the naming referenced in the mount, avoiding the need to
ever reference a /dev/da0p* name after mounting. There are commands that
can use the /dev/gpt/* naming after the mount.

In fact, if I varied the number of other USB drives connected before
booting, then the /dev/da?p* names for the same media could vary from
boot to boot. That makes references messy to handle.

Avoiding ever needing to know the /dev/da?p* name is a good thing in my
view. Referencing the /dev/gpt/* names always just works when they are
how the mounts work.

So, going back to your example, if you mount via /dev/ufs/bar , then in
my view /dev/ufs/bar should not vanish: it should stay usable notation
to reference the device, matching the mount.

> - and on umount /dev/gpt/bar should come back.>
> Regards,
> 
> Stéphane
> 
> 


-- 
===
Mark Millard
marklmi at yahoo.com