Kernel: Allow to disable early boot console

This aid debugging on bare metal when we suspect that the boot console
does something wrong that interferes with other kernel components.

4 files changed, 23 insertions, 4 deletions

diff --git a/Base/usr/share/man/man7/boot_parameters.md b/Base/usr/share/man/man7/boot_parameters.md
index 0a1fc305ae..9618e93a00 100644
--- a/Base/usr/share/man/man7/boot_parameters.md
+++ b/Base/usr/share/man/man7/boot_parameters.md
@@ -35,6 +35,12 @@ List of options:
 
 * **`disable_virtio`** - If present on the command line, virtio devices will not be detected, and initialized on boot.
 
+* **`early_boot_console`** - This parameter expects **`on`** or **`off`** and is by default set to **`on`**.
+  When set to **`off`**, the kernel will not initialize any early console to show kernel dmesg output.
+  When set to **`on`**, the kernel will try to initialize either a text mode console (if VGA text mode was detected)
+  or framebuffer console, based on what the Multiboot bootloader specified on the physical address, width, height
+  and bit color depth.
+
 * **`enable_ioapic`** - This parameter expects **`on`** or **`off`** and is by default set to **`on`**.
   When set to **`off`**, the kernel will initialize the two i8259 PICs.
   When set to **`on`**, the kernel will try to initialize the IOAPIC (or IOAPICs if there's more than one),
diff --git a/Kernel/CommandLine.cpp b/Kernel/CommandLine.cpp
index 1bf2f0a228..8f9d24bdd4 100644
--- a/Kernel/CommandLine.cpp
+++ b/Kernel/CommandLine.cpp
@@ -135,6 +135,16 @@ UNMAP_AFTER_INIT bool CommandLine::is_ioapic_enabled() const
     PANIC("Unknown enable_ioapic setting: {}", value);
 }
 
+UNMAP_AFTER_INIT bool CommandLine::is_early_boot_console_disabled() const
+{
+    auto value = lookup("early_boot_console"sv).value_or("on"sv);
+    if (value == "on"sv)
+        return false;
+    if (value == "off"sv)
+        return true;
+    PANIC("Unknown early_boot_console setting: {}", value);
+}
+
 UNMAP_AFTER_INIT bool CommandLine::is_vmmouse_enabled() const
 {
     return lookup("vmmouse"sv).value_or("on"sv) == "on"sv;
diff --git a/Kernel/CommandLine.h b/Kernel/CommandLine.h
index b4ef9b7fb6..0fe2ef1169 100644
--- a/Kernel/CommandLine.h
+++ b/Kernel/CommandLine.h
@@ -85,6 +85,7 @@ public:
     [[nodiscard]] bool disable_uhci_controller() const;
     [[nodiscard]] bool disable_usb() const;
     [[nodiscard]] bool disable_virtio() const;
+    [[nodiscard]] bool is_early_boot_console_disabled() const;
     [[nodiscard]] AHCIResetMode ahci_reset_mode() const;
     [[nodiscard]] StringView userspace_init() const;
     [[nodiscard]] NonnullOwnPtrVector<KString> userspace_init_args() const;
diff --git a/Kernel/init.cpp b/Kernel/init.cpp
index 3e11be2bf1..a89afa848e 100644
--- a/Kernel/init.cpp
+++ b/Kernel/init.cpp
@@ -195,10 +195,12 @@ extern "C" [[noreturn]] UNMAP_AFTER_INIT void init(BootInfo const& boot_info)
     // NOTE: If the bootloader provided a framebuffer, then set up an initial console.
     // If the bootloader didn't provide a framebuffer, then set up an initial text console.
     // We do so we can see the output on the screen as soon as possible.
-    if (!multiboot_framebuffer_addr.is_null()) {
-        g_boot_console = &try_make_ref_counted<Graphics::BootFramebufferConsole>(multiboot_framebuffer_addr, multiboot_framebuffer_width, multiboot_framebuffer_height, multiboot_framebuffer_pitch).value().leak_ref();
-    } else {
-        g_boot_console = &Graphics::TextModeConsole::initialize().leak_ref();
+    if (!kernel_command_line().is_early_boot_console_disabled()) {
+        if (!multiboot_framebuffer_addr.is_null()) {
+            g_boot_console = &try_make_ref_counted<Graphics::BootFramebufferConsole>(multiboot_framebuffer_addr, multiboot_framebuffer_width, multiboot_framebuffer_height, multiboot_framebuffer_pitch).value().leak_ref();
+        } else {
+            g_boot_console = &Graphics::TextModeConsole::initialize().leak_ref();
+        }
     }
     dmesgln("Starting SerenityOS...");