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

[Heinrich Schuchardt]

On 7/13/24 23:16, Roman Stratiienko wrote:
> 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.

Hello Roman,

could you, please, answer my questions below.

Best regards

Heinrich

>
> 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 =
>>