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