Re: [PATCH v6 11/12] docs: add Btrfs env block and special env vars

Hi Leo,

Thanks for reporting this. I see it has already been merged into git, so
you can simply apply from there now. 

Thanks,
Michael

On Fri, Oct 24, 2025 at 12:18:37PM -0600, Leo Sandoval wrote:
> a minor merge conflict:
> 
> This patch in particular needs to be rebased to latest master
> 
> otherwise I am seeing this on my b4 command
> 
> $ b4 shazam
> https://lore.kernel.org/grub-devel/CAEg-Je8-yE=upFm3RG_4LuG1fRhHGDtco9tEuORE3N3CvqA2Kg@mail.gmail.com/T/#t
> Grabbing thread from
> lore.kernel.org/all/CAEg-Je8-yE%[email protected]/t.mbox.gz
> Checking for newer revisions
> Grabbing search results from lore.kernel.org
> Analyzing 19 messages in the thread
> Analyzing 99 code-review messages
> Checking attestation on all messages, may take a moment...
> ---
>   ✗ [PATCH v6 1/12] misc: add z length modifier support
>   ✗ [PATCH v6 2/12] tests: add z modifier printf tests
>   ✗ [PATCH v6 3/12] util/grub-editenv: add fs_envblk open helper
>   ✗ [PATCH v6 4/12] util/grub-editenv: add fs_envblk write helper
>   ✗ [PATCH v6 5/12] util/grub-editenv: wire set_variables to optional
> fs_envblk
>   ✗ [PATCH v6 6/12] util/grub-editenv: wire unset_variables to optional
> fs_envblk
>   ✗ [PATCH v6 7/12] util/grub-editenv: wire list_variables to optional
> fs_envblk
>   ✗ [PATCH v6 8/12] util/grub-editenv: add probe call for external envblk
>   ✗ [PATCH v6 9/12] btrfs: add environment block to reserved header area
>   ✗ [PATCH v6 10/12] 00_header.in: wire grub.cfg to use env_block when
> present
>   ✗ [PATCH v6 11/12] docs: add Btrfs env block and special env vars
>   ✗ [PATCH v6 12/12] btrfs: update doc link for bootloader support
>   ---
>   ✗ BADSIG: DKIM/suse.com
> ---
> Total patches: 12
> ---
> Applying: misc: add z length modifier support
> Applying: tests: add z modifier printf tests
> Applying: util/grub-editenv: add fs_envblk open helper
> Applying: util/grub-editenv: add fs_envblk write helper
> Applying: util/grub-editenv: wire set_variables to optional fs_envblk
> Applying: util/grub-editenv: wire unset_variables to optional fs_envblk
> Applying: util/grub-editenv: wire list_variables to optional fs_envblk
> Applying: util/grub-editenv: add probe call for external envblk
> Applying: btrfs: add environment block to reserved header area
> Applying: 00_header.in: wire grub.cfg to use env_block when present
> Applying: docs: add Btrfs env block and special env vars
> Patch failed at 0011 docs: add Btrfs env block and special env vars
> error: patch failed: docs/grub.texi:3271
> error: docs/grub.texi: patch does not apply
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> hint: When you have resolved this problem, run "git am --continue".
> hint: If you prefer to skip this patch, run "git am --skip" instead.
> hint: To restore the original branch and stop patching, run "git am
> --abort".
> hint: Disable this message with "git config set advice.mergeConflict false"
> 
> 
> 
> On Fri, Oct 17, 2025 at 3:04 AM Michael Chang via Grub-devel <
> [email protected]> wrote:
> 
> > Update grub.texi to describe the external environment block in the
> > reserved area of Btrfs header used for grub-reboot and savedefault, and
> > add a section documenting the saved_entry, next_entry, and env_block
> > variables.
> >
> > Signed-off-by: Michael Chang <[email protected]>
> > Reviewed-by: Neal Gompa <[email protected]>
> > Reviewed-by: Daniel Kiper <[email protected]>
> > ---
> >  docs/grub.texi | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 60 insertions(+)
> >
> > diff --git a/docs/grub.texi b/docs/grub.texi
> > index 34b3484dc..6ffb3a370 100644
> > --- a/docs/grub.texi
> > +++ b/docs/grub.texi
> > @@ -3271,6 +3271,7 @@ GRUB.  Others may be used freely in GRUB
> > configuration files.
> >  @menu
> >  * Special environment variables::
> >  * Environment block::
> > +* Special environment block variables::
> >  @end menu
> >
> >
> > @@ -3868,9 +3869,68 @@ For safety reasons, this storage is only available
> > when installed on a plain
> >  disk (no LVM or RAID), using a non-checksumming filesystem (no ZFS), and
> >  using BIOS or EFI functions (no ATA, USB or IEEE1275).
> >
> > +On Btrfs filesystems, a reserved area in the filesystem header may be
> > used to
> > +store the environment block. This static block avoids the problems of
> > updating
> > +a normal file on a copy-on-write filesystem, where writing raw block is
> > not
> > +stable and requires metadata update. The reserved area provides a fixed
> > +location that GRUB can update directly, allowing commands such as
> > +@command{grub-reboot} and @samp{GRUB_SAVEDEFAULT} to function correctly on
> > +Btrfs volumes.
> > +
> >  @command{grub-mkconfig} uses this facility to implement
> >  @samp{GRUB_SAVEDEFAULT} (@pxref{Simple configuration}).
> >
> > +
> > +@node Special environment block variables
> > +@section Special environment block variables
> > +
> > +These special variables are usually written to the environment block
> > +(@pxref{Environment block}) to customize the behavior of @file{grub.cfg}
> > +generated by @command{grub-mkconfig}.
> > +
> > +@menu
> > +* saved_entry::
> > +* next_entry::
> > +* env_block::
> > +@end menu
> > +
> > +
> > +@node saved_entry
> > +@subsection saved_entry
> > +
> > +The @var{saved_entry} variable sets the default boot entry in
> > @file{grub.cfg}
> > +created by @command{grub-mkconfig}. It can be set with
> > +@command{grub-set-default} to choose a default entry, or at runtime with
> > the
> > +@code{savedefault} function in grub.cfg to save the current entry as the
> > new
> > +default. This may require write access by GRUB.
> > +
> > +
> > +@node next_entry
> > +@subsection next_entry
> > +
> > +The @var{next_entry} variable sets the boot entry for the next boot only.
> > After
> > +it is used, GRUB clears the value so it is not reused. This requires write
> > +access to the environment block (@pxref{Environment block}) at runtime.
> > The
> > +@command{grub-reboot} command is usually used instead of changing this
> > variable
> > +directly.
> > +
> > +
> > +@node env_block
> > +@subsection env_block
> > +
> > +If the filesystem is Btrfs and the disk is not an abstracted device such
> > as
> > +LVM, RAID, or encryption, the reserved space in the Btrfs header can be
> > used as
> > +the environment block (@pxref{Environment block}). This provides a fixed
> > raw
> > +block that GRUB can reliably write to. The @var{env_block} records this
> > +location in GRUB blocklist syntax (@pxref{Block list syntax}) so that
> > +@command{grub-editenv} and @file{grub.cfg} know how to access and use the
> > +external raw block.
> > +
> > +This variable is initialized when @file{grubenv} is first created by
> > +@command{grub-editenv} and is treated as read-only to avoid being
> > overwritten
> > +with an unpredictable value.
> > +
> > +
> >  @node Modules
> >  @chapter Modules
> >
> > --
> > 2.51.0
> >
> >
> > _______________________________________________
> > Grub-devel mailing list
> > [email protected]
> > https://lists.gnu.org/mailman/listinfo/grub-devel
> >

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