[PATCH] part: efi: Rely on a definition to specify the primary GPT position

[Roman Stratiienko]

Hello Heinrich,

Thank you for your comments.

Just a few thoughts about this patch.

1. I was also sending this patch as a noninvasive, semi-cosmetic
change. Relying on hardcoded values is usually not a good practice.
2. Shifting of primary GPT works in u-boot and Linux kernel with minor
tweaks. See patches [1] and [2] for more context. I'm not going to
upstream them.
3. Accepting this patch upstream helps me to reduce the dependency
chain and potential conflicts during the rebase.

BR, Roman.

[1]: https://github.com/GloDroidCommunity/amlogic-series/blob/8cc5ee7df1358092f77f43aa0c9661883473e5af/patches-aosp/glodroid/bootloader/u-boot/0005-GLODROID-Shift-GPT-position-to-support-Amlogic-platf.patch
[2]: https://github.com/GloDroidCommunity/amlogic-series/blob/8cc5ee7df1358092f77f43aa0c9661883473e5af/patches-aosp/glodroid/kernel/common-android14-6.1-lts/0001-GLODROID-Allow-placing-primary-GPT-to-2MiB-offset-to.patch

пн, 10 черв. 2024 р. о 15:22 Heinrich Schuchardt <xypron.glpk at gmx.de> пише:
>
> On 19.05.24 17:35, Roman Stratiienko wrote:
> > Use GPT_PRIMARY_PARTITION_TABLE_LBA as the only source for a primary GPT
> > location instead of hardcoding it every time.
> >
> > Sometimes, we need to shift the primary GPT location.
> > Having the location in the single place simplifies such shifting.
>
> In gdisk there is an expert command "j - move the main partition table".
> This corresponds to CONFIG_EFI_PARTITION_ENTRIES_OFF. It does not move
> the GPT primary header but only the partition entries. So sector 1 is
> still occupied.
>
> If I read you correctly, CONFIG_EFI_PARTITION_ENTRIES_OFF is not doing
> what you need. Instead of only moving the partition entries of the
> primary partition table, you want to move the complete primary GPT table.
>
> Somehow the operating system must find the primary GPT table.
>
> When writing the partition table shouldn't the offset be reflected in
> the protective MBR fields StartingCHS and StartingLBA? See Table 5.4
> "Protective MBR Partition Record protecting the entire disk*" of the
> UEFI 2.10 specification.
>
> Does Linux support this? For testing remove the backup partition table!
>
> GPT_PRIMARY_PARTITION_TABLE_LBA should be made configurable in this case.
>
> Best regards
>
> Heinrich
>
> >
> > Signed-off-by: Roman Stratiienko <r.stratiienko at gmail.com>
> > ---
> >   disk/part_efi.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/disk/part_efi.c b/disk/part_efi.c
> > index 4ce9243ef2..b55e251ea1 100644
> > --- a/disk/part_efi.c
> > +++ b/disk/part_efi.c
> > @@ -387,7 +387,7 @@ int write_gpt_table(struct blk_desc *desc, gpt_header *gpt_h, gpt_entry *gpt_e)
> >       gpt_h->header_crc32 = cpu_to_le32(calc_crc32);
> >
> >       /* Write the First GPT to the block right after the Legacy MBR */
> > -     if (blk_dwrite(desc, 1, 1, gpt_h) != 1)
> > +     if (blk_dwrite(desc, (lbaint_t)le64_to_cpu(gpt_h->my_lba), 1, gpt_h) != 1)
> >               goto err;
> >
> >       if (blk_dwrite(desc, le64_to_cpu(gpt_h->partition_entry_lba),
> > @@ -534,7 +534,7 @@ int gpt_fill_pte(struct blk_desc *desc,
> >
> >   static uint32_t partition_entries_offset(struct blk_desc *desc)
> >   {
> > -     uint32_t offset_blks = 2;
> > +     uint32_t offset_blks = GPT_PRIMARY_PARTITION_TABLE_LBA + 1;
> >       uint32_t __maybe_unused offset_bytes;
> >       int __maybe_unused config_offset;
> >
> > @@ -572,8 +572,8 @@ static uint32_t partition_entries_offset(struct blk_desc *desc)
> >        * The earliest LBA this can be at is LBA#2 (i.e. right behind
> >        * the (protective) MBR and the GPT header.
> >        */
> > -     if (offset_blks < 2)
> > -             offset_blks = 2;
> > +     if (offset_blks < (GPT_PRIMARY_PARTITION_TABLE_LBA + 1))
> > +             offset_blks = GPT_PRIMARY_PARTITION_TABLE_LBA + 1;
> >
> >       return offset_blks;
> >   }
> > @@ -584,7 +584,7 @@ int gpt_fill_header(struct blk_desc *desc, gpt_header *gpt_h, char *str_guid,
> >       gpt_h->signature = cpu_to_le64(GPT_HEADER_SIGNATURE_UBOOT);
> >       gpt_h->revision = cpu_to_le32(GPT_HEADER_REVISION_V1);
> >       gpt_h->header_size = cpu_to_le32(sizeof(gpt_header));
> > -     gpt_h->my_lba = cpu_to_le64(1);
> > +     gpt_h->my_lba = cpu_to_le64(GPT_PRIMARY_PARTITION_TABLE_LBA);
> >       gpt_h->alternate_lba = cpu_to_le64(desc->lba - 1);
> >       gpt_h->last_usable_lba = cpu_to_le64(desc->lba - 34);
> >       gpt_h->partition_entry_lba =
>