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

[Heinrich Schuchardt]

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.

Best regards

Heinrich 

>+		for (row = 1; row < efi_cout_modes[efi_con_mode.mode].rows; row++)
>+			printf("\n");
>+	}
>+
> 	/*
> 	 * The Linux console wants both a clear and a home command. The video
> 	 * uclass does not support <ESC>[H without coordinates, yet.