On Thu, Oct 02, 2025 at 02:46:20PM +0800, Michael Chang via Grub-devel wrote:
> This patch reserves space for the GRUB environment block inside the
> Btrfs header. The block is placed at an offset of 256 KiB from the start
> of the device and occupies one sector. To protect the space, overflow
> guard sectors are placed before and after the reserved block.
>
> The Btrfs header already defines regions for bootloader use. By adding
> this entry, GRUB gains a fixed and safe location to store the
> environment block without conflicting with other structures in the
> header.
>
> Signed-off-by: Michael Chang <[email protected]>
> Reviewed-by: Neal Gompa <[email protected]>
> ---
> grub-core/fs/btrfs.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index 7bf8d922f..d35ff5fa5 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -2341,7 +2341,7 @@ struct embed_region {
>
> static const struct {
> struct embed_region available;
> - struct embed_region used[6];
> + struct embed_region used[7];
> } btrfs_head = {
> .available = {0, GRUB_DISK_KiB_TO_SECTORS (1024)}, /* The first 1 MiB. */
> .used = {
> @@ -2349,6 +2349,7 @@ static const struct {
> {GRUB_DISK_KiB_TO_SECTORS (64) - 1, 1}, /*
> Overflow guard. */
> {GRUB_DISK_KiB_TO_SECTORS (64), GRUB_DISK_KiB_TO_SECTORS (4)}, /* 4 KiB
> superblock. */
> {GRUB_DISK_KiB_TO_SECTORS (68), 1}, /*
> Overflow guard. */
> + {(ENV_BTRFS_OFFSET >> GRUB_DISK_SECTOR_BITS) - 1, 3}, /*
> Environment Block. */
{(ENV_BTRFS_OFFSET >> GRUB_DISK_SECTOR_BITS) - 1, 1}, /* Overflow guard. */
{(ENV_BTRFS_OFFSET >> GRUB_DISK_SECTOR_BITS), 1}, /* Environment block. */
{(ENV_BTRFS_OFFSET >> GRUB_DISK_SECTOR_BITS) + 1, 1}, /* Overflow guard. */
> {GRUB_DISK_KiB_TO_SECTORS (1024) - 1, 1}, /*
> Overflow guard. */
> {0, 0} /* Array
> terminator. */
Plus comments from patch #1...
And could you add a patch which updates outdated link to the Btrfs
documentation just before btrfs_head variable?
Daniel
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