Currently, add_preferred_console sets a preferred console, but doesn't
actually change /dev/console to match it. That part is handled within
register_device, where a newly registered console driver will be set as
/dev/console if it matches the preferred console.
However, if the relevant driver is already registered, the only way to
set it as /dev/console is by un-registering and re-registering it. An
example is the xenfb_make_preferred_console() function:
console_lock();
for_each_console(c) {
if (!strcmp(c->name, "tty") && c->index == 0)
break;
}
console_unlock();
if (c) {
unregister_console(c);
c->flags |= CON_CONSDEV;
c->flags &= ~CON_PRINTBUFFER; /* don't print again */
register_console(c);
}
The code above was introduced in commit 9e124fe16ff2 ("xen: Enable
console tty by default in domU if it's not a dummy"). In short, it's aim
is to set VT as the preferred console only after a working framebuffer
is registered and thus VT is not the dummy device.
This patch introduces an update_console_to_preferred function that
handles the necessary /dev/console change. With this change, the example
above can be replaced with:
console_lock();
add_preferred_console("tty", 0, NULL);
update_console_to_preferred();
console_unlock();
More importantly, these two calls can be moved to vt.c in order to bump
its priority when a non-dummy backend for it is introduced, solving that
problem in general.
Signed-off-by: Alper Nebi Yasak <[email protected]>
---
Changes in v2:
- Use the correct format when referencing a commit
include/linux/console.h | 1 +
kernel/printk/printk.c | 56 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 57 insertions(+)
diff --git a/include/linux/console.h b/include/linux/console.h
index 75dd20650fbe..4b3fa34be245 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -172,6 +172,7 @@ enum con_flush_mode {
};
extern int add_preferred_console(char *name, int idx, char *options);
+extern int update_console_to_preferred(void);
extern void register_console(struct console *);
extern int unregister_console(struct console *);
extern struct console *console_drivers;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6ede4a7222e6..efda422203e4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2240,12 +2240,68 @@ __setup("console=", console_setup);
* be used by arch-specific code either to override the user or more
* commonly to provide a default console (ie from PROM variables) when
* the user has not supplied one.
+ *
+ * Preferences set by this function don't take effect until the next
+ * time a matching driver for the preferred console is registered. If a
+ * matching driver was already registered, @update_console_to_preferred
+ * function can be used to set that as the preferred console driver.
*/
int add_preferred_console(char *name, int idx, char *options)
{
return __add_preferred_console(name, idx, options, NULL, false);
}
+/**
+ * update_console_to_preferred - set console to the preferred console's driver.
+ *
+ * Updates console_drivers and CON_CONSDEV flags so that an already
+ * registered and enabled console driver matching the preferred console
+ * is used as /dev/console.
+ *
+ * Must be called within console_lock();.
+ */
+int update_console_to_preferred(void)
+{
+ struct console_cmdline *c = NULL;
+ struct console *con = NULL;
+ struct console *tmp = NULL;
+
+ if (preferred_console >= 0)
+ c = &console_cmdline[preferred_console];
+
+ if (!c || !c->name[0])
+ return 0;
+
+ for_each_console(con) {
+ if (!con->next || !(con->next->flags & CON_ENABLED))
+ continue;
+ if (strcmp(c->name, con->next->name) != 0)
+ continue;
+ if (con->next->index >= 0 &&
+ con->next->index != c->index)
+ continue;
+ break;
+ }
+
+ if (!con)
+ return -ENODEV;
+
+ pr_info("switching to console [%s%d]\n",
+ con->next->name, con->next->index);
+
+ tmp = con->next;
+ con->next = con->next->next;
+ tmp->next = console_drivers;
+ console_drivers = tmp;
+
+ if (console_drivers->next)
+ console_drivers->next->flags &= ~CON_CONSDEV;
+ console_drivers->flags |= CON_CONSDEV;
+ has_preferred_console = true;
+
+ return 0;
+}
+
bool console_suspend_enabled = true;
EXPORT_SYMBOL(console_suspend_enabled);
--
2.26.2
