Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens,
as console messages may appear before the splash screen. So check the
command line for the expectation of userspace splash and if present then
extend the deferral until the first switch.
v2: Added Kconfig option instead of hard coding "splash".
v3: Default to disabled, not "splash". If enabled then take over on
switch rather than on first output after switch.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello <[email protected]>
Signed-off-by: Daniel van Vugt <[email protected]>
---
drivers/video/console/Kconfig | 12 +++++++++
drivers/video/fbdev/core/fbcon.c | 44 +++++++++++++++++++++++++++++---
2 files changed, 52 insertions(+), 4 deletions(-)
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index bc31db6ef7..2f9435335f 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -138,6 +138,18 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
by the firmware in place, rather then replacing the contents with a
black screen as soon as fbcon loads.
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ string "Command line parameter to defer takeover to first switch"
+ depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+ default ""
+ help
+ If enabled this defers further the framebuffer console taking over
+ until the first console switch has occurred. And even then only if
+ the specified parameter is found on the command line. This ensures
+ fbcon does not interrupt userspace splash screens such as Plymouth
+ which may be yet to start rendering at the time of the first console
+ output.
+
config STI_CONSOLE
bool "STI text console"
depends on PARISC && HAS_IOMEM
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 1183e7a871..e5d841ab03 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include <linux/crc32.h> /* For counting font checksums */
#include <linux/uaccess.h>
#include <asm/irq.h>
+#include <asm/cmdline.h>
#include "fbcon.h"
#include "fb_internal.h"
@@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block *nb,
{
WARN_CONSOLE_UNLOCKED();
- pr_info("fbcon: Taking over console\n");
+ pr_info("fbcon: Taking over console for output\n");
dummycon_unregister_output_notifier(&fbcon_output_nb);
@@ -3357,6 +3358,27 @@ static int fbcon_output_notifier(struct notifier_block *nb,
return NOTIFY_OK;
}
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+static int initial_console;
+static struct notifier_block fbcon_switch_nb;
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ pr_info("fbcon: Taking over console for switch\n");
+ dummycon_unregister_switch_notifier(&fbcon_switch_nb);
+ schedule_work(&fbcon_deferred_takeover_work);
+ }
+
+ return NOTIFY_OK;
+}
+#endif
#endif
static void fbcon_start(void)
@@ -3368,8 +3390,18 @@ static void fbcon_start(void)
deferred_takeover = false;
if (deferred_takeover) {
- fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(&fbcon_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ if (cmdline_find_option_bool(boot_command_line,
+ CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
+ initial_console = fg_console;
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ dummycon_register_switch_notifier(&fbcon_switch_nb);
+ } else
+#endif
+ {
+ fbcon_output_nb.notifier_call = fbcon_output_notifier;
+ dummycon_register_output_notifier(&fbcon_output_nb);
+ }
return;
}
#endif
@@ -3416,8 +3448,12 @@ void __exit fb_console_exit(void)
{
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
console_lock();
- if (deferred_takeover)
+ if (deferred_takeover) {
dummycon_unregister_output_notifier(&fbcon_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ dummycon_unregister_switch_notifier(&fbcon_switch_nb);
+#endif
+ }
console_unlock();
cancel_work_sync(&fbcon_deferred_takeover_work);
--
2.43.0
On 2/13/2024 23:24, Daniel van Vugt wrote:
> Until now, deferred console takeover only meant defer until there is
> output. But that risks stepping on the toes of userspace splash screens,
> as console messages may appear before the splash screen. So check the
> command line for the expectation of userspace splash and if present then
> extend the deferral until the first switch.
I think your comment from the earlier version that this can still happen
on simpledrm (albeit less frequently) is very relevant here for the
commit message.
>
> v2: Added Kconfig option instead of hard coding "splash".
> v3: Default to disabled, not "splash". If enabled then take over on
> switch rather than on first output after switch.
>
These you'll want below the cutlist (---)
Also I think you should mention in the commit message that the
indication of a userspace splash is set by the Kconfig.
> Closes: https://bugs.launchpad.net/bugs/1970069
> Cc: Mario Limonciello <[email protected]>
> Signed-off-by: Daniel van Vugt <[email protected]>
> ---
> drivers/video/console/Kconfig | 12 +++++++++
> drivers/video/fbdev/core/fbcon.c | 44 +++++++++++++++++++++++++++++---
> 2 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index bc31db6ef7..2f9435335f 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -138,6 +138,18 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> by the firmware in place, rather then replacing the contents with a
> black screen as soon as fbcon loads.
>
> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + string "Command line parameter to defer takeover to first switch"
> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> + default ""
> + help
> + If enabled this defers further the framebuffer console taking over
> + until the first console switch has occurred. And even then only if
> + the specified parameter is found on the command line. This ensures
> + fbcon does not interrupt userspace splash screens such as Plymouth
> + which may be yet to start rendering at the time of the first console
> + output.
> +
> config STI_CONSOLE
> bool "STI text console"
> depends on PARISC && HAS_IOMEM
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 1183e7a871..e5d841ab03 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -76,6 +76,7 @@
> #include <linux/crc32.h> /* For counting font checksums */
> #include <linux/uaccess.h>
> #include <asm/irq.h>
> +#include <asm/cmdline.h>
>
> #include "fbcon.h"
> #include "fb_internal.h"
> @@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block *nb,
> {
> WARN_CONSOLE_UNLOCKED();
>
> - pr_info("fbcon: Taking over console\n");
> + pr_info("fbcon: Taking over console for output\n");
>
> dummycon_unregister_output_notifier(&fbcon_output_nb);
>
> @@ -3357,6 +3358,27 @@ static int fbcon_output_notifier(struct notifier_block *nb,
>
> return NOTIFY_OK;
> }
> +
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> +static int initial_console;
> +static struct notifier_block fbcon_switch_nb;
> +
> +static int fbcon_switch_notifier(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct vc_data *vc = data;
> +
> + WARN_CONSOLE_UNLOCKED();
> +
> + if (vc->vc_num != initial_console) {
> + pr_info("fbcon: Taking over console for switch\n");
> + dummycon_unregister_switch_notifier(&fbcon_switch_nb);
> + schedule_work(&fbcon_deferred_takeover_work);
> + }
> +
> + return NOTIFY_OK;
> +}
> +#endif
> #endif
Once you start adding nested #ifdef, I think it's very useful to add a
comment on the #endif to make it easier to follow the code.
IE
#endif /* CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION */
>
> static void fbcon_start(void)
> @@ -3368,8 +3390,18 @@ static void fbcon_start(void)
> deferred_takeover = false;
>
> if (deferred_takeover) {
> - fbcon_output_nb.notifier_call = fbcon_output_notifier;
> - dummycon_register_output_notifier(&fbcon_output_nb);
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + if (cmdline_find_option_bool(boot_command_line,
> + CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
> + initial_console = fg_console;
> + fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
> + dummycon_register_switch_notifier(&fbcon_switch_nb);
> + } else
> +#endif
> + {
> + fbcon_output_nb.notifier_call = fbcon_output_notifier;
> + dummycon_register_output_notifier(&fbcon_output_nb);
> + }
> return;
> }
> #endif
> @@ -3416,8 +3448,12 @@ void __exit fb_console_exit(void)
> {
> #ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> console_lock();
> - if (deferred_takeover)
> + if (deferred_takeover) {
> dummycon_unregister_output_notifier(&fbcon_output_nb);
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + dummycon_unregister_switch_notifier(&fbcon_switch_nb);
> +#endif
> + }
> console_unlock();
>
> cancel_work_sync(&fbcon_deferred_takeover_work);
To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.
Signed-off-by: Daniel van Vugt <[email protected]>
---
drivers/video/console/dummycon.c | 35 +++++++++++++++++++++++++++-----
include/linux/console.h | 2 ++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
/* Redraw, so that we get putc(s) for output done while blanked */
return 1;
}
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_register(&dummycon_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_unregister(&dummycon_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_call_chain(&dummycon_switch_nh, 0, vc);
+
+ return 0;
+}
#else
static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
{
return 0;
}
+static int dummycon_switch(struct vc_data *vc)
+{
+ return 0;
+}
#endif
static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned int top,
return false;
}
-static int dummycon_switch(struct vc_data *vc)
-{
- return 0;
-}
-
/*
* The console `switch' structure for the dummy console
*
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
#endif /* _LINUX_CONSOLE_H */
--
2.43.0
Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens
as console messages may appear before the splash screen.
This becomes more likely the later the splash screen starts, but even
systems whose splash exists in initrd may not be not immune because they
still rely on racing against all possible kernel messages that might
trigger the fbcon takeover. And those kernel messages are hardware
dependent so what boots silently on one machine may not be so quiet on
the next. We also want to shield users from seeing warnings about their
hardware/firmware that they don't always have the power to fix themselves,
and may not be deemed worthy of fixing by the vendor.
So now we check the command line for the expectation of userspace splash
(CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION) and if present
then defer fbcon's takeover until the first console switch. In the case
of Plymouth, its value would typically be "splash". This keeps the boot
experience clean and silent so long as the command line requests so.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello <[email protected]>
Signed-off-by: Daniel van Vugt <[email protected]>
---
v2: Added Kconfig option instead of hard coding "splash".
v3: Default to disabled, not "splash". If enabled then take over on
switch rather than on first output after switch.
v4: Elaborate more in the commit message about races and Kconfig. Also
move these revision comments below the line marker.
---
drivers/video/console/Kconfig | 12 +++++++++
drivers/video/fbdev/core/fbcon.c | 44 +++++++++++++++++++++++++++++---
2 files changed, 52 insertions(+), 4 deletions(-)
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index bc31db6ef7..2f9435335f 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -138,6 +138,18 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
by the firmware in place, rather then replacing the contents with a
black screen as soon as fbcon loads.
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ string "Command line parameter to defer takeover to first switch"
+ depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+ default ""
+ help
+ If enabled this defers further the framebuffer console taking over
+ until the first console switch has occurred. And even then only if
+ the specified parameter is found on the command line. This ensures
+ fbcon does not interrupt userspace splash screens such as Plymouth
+ which may be yet to start rendering at the time of the first console
+ output.
+
config STI_CONSOLE
bool "STI text console"
depends on PARISC && HAS_IOMEM
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 1183e7a871..e5d841ab03 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include <linux/crc32.h> /* For counting font checksums */
#include <linux/uaccess.h>
#include <asm/irq.h>
+#include <asm/cmdline.h>
#include "fbcon.h"
#include "fb_internal.h"
@@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block *nb,
{
WARN_CONSOLE_UNLOCKED();
- pr_info("fbcon: Taking over console\n");
+ pr_info("fbcon: Taking over console for output\n");
dummycon_unregister_output_notifier(&fbcon_output_nb);
@@ -3357,6 +3358,27 @@ static int fbcon_output_notifier(struct notifier_block *nb,
return NOTIFY_OK;
}
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+static int initial_console;
+static struct notifier_block fbcon_switch_nb;
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ pr_info("fbcon: Taking over console for switch\n");
+ dummycon_unregister_switch_notifier(&fbcon_switch_nb);
+ schedule_work(&fbcon_deferred_takeover_work);
+ }
+
+ return NOTIFY_OK;
+}
+#endif
#endif
static void fbcon_start(void)
@@ -3368,8 +3390,18 @@ static void fbcon_start(void)
deferred_takeover = false;
if (deferred_takeover) {
- fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(&fbcon_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ if (cmdline_find_option_bool(boot_command_line,
+ CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
+ initial_console = fg_console;
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ dummycon_register_switch_notifier(&fbcon_switch_nb);
+ } else
+#endif
+ {
+ fbcon_output_nb.notifier_call = fbcon_output_notifier;
+ dummycon_register_output_notifier(&fbcon_output_nb);
+ }
return;
}
#endif
@@ -3416,8 +3448,12 @@ void __exit fb_console_exit(void)
{
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
console_lock();
- if (deferred_takeover)
+ if (deferred_takeover) {
dummycon_unregister_output_notifier(&fbcon_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ dummycon_unregister_switch_notifier(&fbcon_switch_nb);
+#endif
+ }
console_unlock();
cancel_work_sync(&fbcon_deferred_takeover_work);
--
2.43.0
Hi Daniel,
On Mon, Feb 19, 2024 at 05:02:34PM +0800, Daniel van Vugt wrote:
> Until now, deferred console takeover only meant defer until there is
> output. But that risks stepping on the toes of userspace splash screens
> as console messages may appear before the splash screen.
>
> This becomes more likely the later the splash screen starts, but even
> systems whose splash exists in initrd may not be not immune because they
> still rely on racing against all possible kernel messages that might
> trigger the fbcon takeover. And those kernel messages are hardware
> dependent so what boots silently on one machine may not be so quiet on
> the next. We also want to shield users from seeing warnings about their
> hardware/firmware that they don't always have the power to fix themselves,
> and may not be deemed worthy of fixing by the vendor.
>
> So now we check the command line for the expectation of userspace splash
> (CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION) and if present
> then defer fbcon's takeover until the first console switch. In the case
> of Plymouth, its value would typically be "splash". This keeps the boot
> experience clean and silent so long as the command line requests so.
>
> Closes: https://bugs.launchpad.net/bugs/1970069
> Cc: Mario Limonciello <[email protected]>
> Signed-off-by: Daniel van Vugt <[email protected]>
It's not clear to me why we should want to make it an option? If one
strategy is better than the other, and I guess the new one is if you
consider it fixes a bug and bothered to submit it upstream, why not just
get rid of the old one entirely?
I guess my question is: why do we want the choice, and what are the
tradeoff each strategy brings?
Maxime
On 2/22/2024 05:08, Maxime Ripard wrote:
> Hi Daniel,
>
> On Mon, Feb 19, 2024 at 05:02:34PM +0800, Daniel van Vugt wrote:
>> Until now, deferred console takeover only meant defer until there is
>> output. But that risks stepping on the toes of userspace splash screens
>> as console messages may appear before the splash screen.
>>
>> This becomes more likely the later the splash screen starts, but even
>> systems whose splash exists in initrd may not be not immune because they
>> still rely on racing against all possible kernel messages that might
>> trigger the fbcon takeover. And those kernel messages are hardware
>> dependent so what boots silently on one machine may not be so quiet on
>> the next. We also want to shield users from seeing warnings about their
>> hardware/firmware that they don't always have the power to fix themselves,
>> and may not be deemed worthy of fixing by the vendor.
>>
>> So now we check the command line for the expectation of userspace splash
>> (CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION) and if present
>> then defer fbcon's takeover until the first console switch. In the case
>> of Plymouth, its value would typically be "splash". This keeps the boot
>> experience clean and silent so long as the command line requests so.
>>
>> Closes: https://bugs.launchpad.net/bugs/1970069
>> Cc: Mario Limonciello <[email protected]>
>> Signed-off-by: Daniel van Vugt <[email protected]>
I did test this series on an Ubuntu userspace and it works as you
suggest it should.
Tested-by: Mario Limonciello <[email protected]>
>
> It's not clear to me why we should want to make it an option? If one
> strategy is better than the other, and I guess the new one is if you
> consider it fixes a bug and bothered to submit it upstream, why not just
> get rid of the old one entirely?
>
> I guess my question is: why do we want the choice, and what are the
> tradeoff each strategy brings?
>
> Maxime
The reason for choice is that it keys off a kernel command line
parameter that is inconsistent across distributions.
For example Ubuntu uses "splash", Fedora used "rhgb" etc.
Even the plymouth userspace maintains a list for it's behaviors of what
parameters to look for to start at bootup. So the obvious alternative
is to clone that list in the kernel.