[DragonFlyBSD - Bug #3401] mount(8) doesn't detect filesystem type in raw GPT partition

[sigttou]

Issue #3401 has been updated by sigttou.

File mount-gpt-fstype.patch added

mount(8) only guesses the filesystem from the legacy disklabel fstype.
gpt_setslice() puts the GPT partition type UUID in partinfo.fstype_uuid
(DIOCGPART), but mount(8) never looks at it.  A raw GPT slice has fstype
0, so mount warns and falls back to ufs.

Fix: in checkdisklabel(), if the legacy fstype does not map, look the
fstype_uuid up in a table of GPT partition types (EFI -> msdos, the
DragonFly/FreeBSD native types -> ufs/hammer/hammer2).  Unknown types
keep the old warning and ufs fallback.

Repro:

 vnconfig vn0 img
gpt create vn0
gpt add -t efi vn0
newfs_msdos /dev/vn0s0
mount /dev/vn0s0 /mnt

before: warning, "attempting to mount with -t ufs", mount_ufs fails
after:  mounts as msdos

----------------------------------------
Bug #3401: mount(8) doesn't detect filesystem type in raw GPT partition
http://bugs.dragonflybsd.org/issues/3401#change-14715

* Author: liweitianux
* Status: New
* Priority: Normal
* Category: Userland
* Target version: 6.6
* Start date: 2026-02-23
----------------------------------------
mount(8) tries to guess/detect the FS type for a partition within a BSD disklabel. However, it doesn't guess the FS type for a raw GPT partition, e.g.,

<pre>
% sudo gpt show vn4
Disk vn4: 2048MB (4194304 512-byte sectors)
    Start  Sectors    Size  Index  Contents
        0        1    512B      -  PMBR
        1        1    512B      -  Pri GPT header
        2       32  16.0KB      -  Pri GPT table
       34     2014  1007KB      -  Unused
     2048  2000896   977MB      0  GPT part - EFI System
  2002944  2191327  1070MB      -  Unused
  4194271       32  16.0KB      -  Sec GPT table
  4194303        1    512B      -  Sec GPT header

% sudo newfs_msdos vn4s0
/dev/vn4s0: 2000352 sectors in 62511 FAT16 clusters (16384 bytes/cluster)
BytesPerSec=512 SecPerClust=32 ResSectors=1 FATs=2 RootDirEnts=512 Media=0xf0 FATsecs=245 SecPerTrack=32 Heads=64 HiddenSecs=0 HugeSectors=2000896

% sudo mount /dev/vn4s0 /mnt/tmp
mount: warning: fstype in disklabel not set to anything I understand
attempting to mount with -t ufs
mount_ufs: /dev/vn4s0 on /mnt/tmp: incorrect super block
</pre>

---Files--------------------------------
mount-gpt-fstype.patch (2.43 KB)


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