[PATCH v4 1/2] efi_loader: Avoid overwriting previous outputs on console screen clearing

[Jan Kiszka]

On 18.01.23 21:56, Heinrich Schuchardt wrote:
> 
> 
> Am 18. Januar 2023 21:44:58 MEZ schrieb Jan Kiszka <jan.kiszka at siemens.com>:
>> From: Jan Kiszka <jan.kiszka at siemens.com>
>>
>> Before clearing the screen, ensure that no previous output of firmware
>> or UEFI programs will be overwritten on serial devices or other
>> streaming consoles. This helps generating complete boot logs.
>>
>> Tested regarding multi-output against qemu-x86_defconfig. Still, there
>> were remaining concerns about side effects, so this is provided as an
>> opt-in feature.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>
>> ---
>> lib/efi_loader/Kconfig       |  9 +++++++++
>> lib/efi_loader/efi_console.c | 10 +++++++++-
>> 2 files changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
>> index b498c72206f..b2c3250b4ad 100644
>> --- a/lib/efi_loader/Kconfig
>> +++ b/lib/efi_loader/Kconfig
>> @@ -124,6 +124,15 @@ config EFI_SET_TIME
>> 	  Provide the SetTime() runtime service at boottime. This service
>> 	  can be used by an EFI application to adjust the real time clock.
>>
>> +config EFI_SCROLL_ON_CLEAR_SCREEN
>> +	bool "Avoid overwriting previous output on clear screen"
>> +	help
>> +	  Instead of moving the cursor home when the console screen should be
>> +	  cleared, emit blank new lines so that previous output is scrolled
>> +	  out of sight rather than overwritten. This allows on serial consoles
>> +	  to capture complete boot logs (except for interactive menus etc.)
>> +	  and can ease debugging related issues.
>> +
>> config EFI_HAVE_CAPSULE_SUPPORT
>> 	bool
>>
>> diff --git a/lib/efi_loader/efi_console.c b/lib/efi_loader/efi_console.c
>> index 4d08dd3763a..e40c129d1b2 100644
>> --- a/lib/efi_loader/efi_console.c
>> +++ b/lib/efi_loader/efi_console.c
>> @@ -461,10 +461,18 @@ static efi_status_t EFIAPI efi_cout_set_attribute(
>> }
>>
>> /**
>> - * efi_cout_clear_screen() - clear screen
>> + * efi_clear_screen() - clear screen
>>  */
>> static void efi_clear_screen(void)
>> {
>> +	if (CONFIG_IS_ENABLED(EFI_SCROLL_ON_CLEAR_SCREEN)) {
>> +		unsigned int row;
>> +
>> +		/* Avoid overwriting previous outputs on streaming consoles */
> 
> Thanks for making the behavior configurable.
> 
> We cannot assume that the cursor is on the last line. 
> 
> Assume that the cursor is on the first line. Then the screen will still be deleted.
> 
> Especially in GRUB the cursor often is in the upper half of the screen
> 
> The cursor should be moved to the right lower corner before scrolling.

Can do, though logging interactive menus was not in scope (and can't be
solved this way anyway).

Jan

-- 
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