Re: [PATCH v6 00/12] Add support for external environment block on Btrfs

On Mon, Oct 27, 2025 at 04:55:41PM -0400, Neal Gompa wrote:
> On Mon, Oct 20, 2025 at 11:04 AM Daniel Kiper <[email protected]> wrote:
> > On Fri, Oct 17, 2025 at 05:01:31PM +0800, Michael Chang via Grub-devel wrote:
> > > This patch series adds support for storing the GRUB environment block in
> > > a reserved area of the Btrfs header. On copy on write filesystems such
> > > as Btrfs, the normal file based envblk cannot be updated safely at
> > > runtime because block addresses are not stable. The reserved area
> > > provides a fixed location that GRUB can write directly, allowing
> > > commands such as grub-reboot and savedefault to work on Btrfs volumes.
> > >
> > > The series proceeds in small chunks to keep each change buildable and
> > > easier to review. The first patches add new data structures and helpers
> > > for creating, opening, and writing an environment block in the reserved
> > > area. Later patches update set_variables, unset_variables, and
> > > list_variables so they can use the external block when it is present. An
> > > entry is added to the Btrfs header to reserve space at 256 KiB for the
> > > environment block. Finally, grub.cfg is modified so that load_env and
> > > save_env use the external block automatically when env_block is defined.
> > >
> > > The first two patches are new in this series as feedback from the review
> > > to use a portable string specifier for size_t. Unfortunately the z
> > > length modifier is missing in GRUB printf routine's format specifier.
> > > The new patches add support and test case for that. In theory they can
> > > be reviewed separately.
> > >
> > > And also yet another new patch "btrfs: update doc link for bootloader
> > > support" added at the end to address v3 review feedback.
> > >
> > > v2:
> > > - Define ENV_BTRFS_OFFSET as 256*1024
> > > - Do not conflate type and variable definitions
> > > - Align typedef with struct declaration to follow coding style
> > > - Use bool as the return type of is_abstraction()
> > > - Add "if (dev->disk != NULL)" check in is_abstraction()
> > > - Refine the loop logic in is_abstraction() tests
> > > - Remove extra indentation and redundant lines in read_envblk_fs
> > > - Use off_t and size_t for offset and size variables, fix similar cases
> > >   throughout
> > > - Use explicit check "(fp == NULL)" instead of "(! fp)", fix similar
> > >   cases throughout
> > > - Use bool for the "found" field in var_lookup_ctx
> > > - Add documentation describing the Btrfs environment block and special
> > >   environment block variables
> > > v3:
> > > - Replace !fp with explicit (fp == NULL) for clarity
> > > - Fix missing blank line before return statement
> > > - Fix missing space after cast operator
> > > v4:
> > > - Rename ENV_BTRFS_OFFSET to GRUB_ENV_BTRFS_OFFSET
> > > - Move GRUB_ENV_BTRFS_OFFSET into "btrfs: add environment block to
> > >   reserved header area"
> > > - Adjust patch order to resolve relocated GRUB_ENV_BTRFS_OFFSET
> > > - Add patch "btrfs: update doc link for bootloader support"
> > > - Do better typedef
> > > - Add heads-up comments to both fs_envblk_spec and btrfs_head that they
> > >   have to stay in sync
> > > - Fix a few places to use explicit checks for NULL, true/false etc
> > > - Use goto labels to cleanup consistently
> > > - Mark function names with trailing "()" in commits and comments
> > > - Rename envblk_fs to envblk_on_block for better clarity
> > > - Avoid redundant curly braces in if .. else if clause
> > > - Highlight overflow guard around envioronment block in embed_region
> > > - Rename a few functions for clarity
> > > - Use portable printf formats for off_t and size_t
> > > - Support z length modifier in GRUB printf format string
> > > - Add z modifier to printf unit test
> > > v5:
> > > - Move fs_envblk_spec table into "btrfs: add environment block to
> > >   reserved header area"
> > > - Move "util/grub-editenv: add basic structures and probe call for
> > >   external envblk" the 9th patch behind all wiring patches and rename it
> > >   to "util/grub-editenv: add probe call for external envblk" as it now
> > >   only does probing
> > > - Add fs_envblk_init() to wire open helper in the base structures into
> > >   patch "util/grub-editenv: add fs_envblk open helper"
> > > - Add "Man 5 btrfs" an alternate to the doc link
> > > v6:
> > > - Move fs_envblk_spec structure typedef and variable from "btrfs: add
> > >   environment block to reserved header area" into "util/grub-editenv:
> > >   add fs_envblk open helper". The fs_envblk_spec remains empty since no
> > >   Btrfs area is defined yet.
> > > - Reorder "btrfs: add environment block to reserved header area" to
> > >   follow all groundwork patches, and provide the defined reserved area
> > >   to fs_envblk_spec so that it becomes supported in grub-editenv.
> > >
> > > Michael Chang (12):
> > >   misc: add z length modifier support
> > >   tests: add z modifier printf tests
> > >   util/grub-editenv: add fs_envblk open helper
> > >   util/grub-editenv: add fs_envblk write helper
> > >   util/grub-editenv: wire set_variables to optional fs_envblk
> > >   util/grub-editenv: wire unset_variables to optional fs_envblk
> > >   util/grub-editenv: wire list_variables to optional fs_envblk
> > >   util/grub-editenv: add probe call for external envblk
> > >   btrfs: add environment block to reserved header area
> > >   00_header.in: wire grub.cfg to use env_block when present
> > >   docs: add Btrfs env block and special env vars
> > >   btrfs: update doc link for bootloader support
> >
> > For all patches Reviewed-by: Daniel Kiper <[email protected]>...
>
> Sorry for resending this but it occurred to me that I was using the
> wrong email, so I'm asking again if this can land in time for GRUB 2.14?

If you take a look at the GRUB git repository you will see that relevant
patches are in for a few days...

Daniel

_______________________________________________
Grub-devel mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/grub-devel