git: kernel: Assume s0 (compatibility slice) for any unformatted disk

[Aaron LI]

commit b73d6e474c7b35d6ee6626f0443020ad40e2ebc6
Author: Aaron LI <aly at aaronly.me>
Date:   Thu Mar 5 19:38:53 2026 +0800

    kernel: Assume s0 (compatibility slice) for any unformatted disk
    
    In commit 8cf8601ebae6a54f01fe9a7aed045832fc6a903b I changed the kernel
    to ignore a disk without MBR or GPT, instead of assuming there is the
    compatibility slice (s0) covering the whole disk.  A later commit
    f687b277b90809ae7df59f012ba2c7312b608545 only made a special case
    for vn(4) disk because our nrelease procedure uses such a behavior.
    
    This behavior change might cause real trouble for those users that
    actually use the compatibility slice.  A filesystem previously created
    directly on an unformatted disk would disappear and unusable on the new
    kernel.  What's worse, there is no empty space at the disk beginning to
    create a MBR for migration.
    
    This partially reverts commit f687b277b90809ae7df59f012ba2c7312b608545
    and brings back the s0 compatibility slice for any disk that doesn't
    have a MBR/GPT header (i.e., unformatted disks).
    
    While there, adjust the kernel message to be more descriptive.
    
    See more discussion at: https://lists.dragonflybsd.org/pipermail/users/2026-March/452614.html

Summary of changes:
 sys/dev/disk/vn/vn.c    | 4 ++--
 sys/kern/subr_diskmbr.c | 9 ++-------
 sys/sys/disk.h          | 6 +-----
 sys/sys/param.h         | 3 ++-
 4 files changed, 7 insertions(+), 15 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/b73d6e474c7b35d6ee6626f0443020ad40e2ebc6


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