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Message-ID: <20190311133341.vqcagdo4e4vy6dfu@pathway.suse.cz>
Date: Mon, 11 Mar 2019 14:33:41 +0100
From: Petr Mladek <pmladek@...e.com>
To: Calvin Owens <calvinowens@...com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
linux-serial@...r.kernel.org
Subject: Re: [PATCH 3/4] printk: Add consoles to a virtual "console" bus
On Fri 2019-03-01 16:48:19, Calvin Owens wrote:
> This patch embeds a device struct in the console struct, and registers
> them on a "console" bus so we can expose attributes in sysfs.
>
> Currently, most drivers declare static console structs, and that is
> incompatible with the dev refcount model. So we end up needing to patch
> all of the console drivers to:
>
> 1. Dynamically allocate the console struct using a new helper
> 2. Handle the allocation in (1) possibly failing
> 3. Dispose of (1) with put_device()
>
> Early console structures must still be static, since they're required
> before we're able to allocate memory. The least ugly way I can come up
> with to handle this is an "is_static" flag in the structure which makes
> the gets and puts NOPs, and is checked in ->release() to catch mistakes.
>
> diff --git a/drivers/char/lp.c b/drivers/char/lp.c
> index 5c8d780637bd..e09cb192a469 100644
> --- a/drivers/char/lp.c
> +++ b/drivers/char/lp.c
> @@ -857,12 +857,12 @@ static void lp_console_write(struct console *co, const char *s,
> parport_release(dev);
> }
>
> -static struct console lpcons = {
> - .name = "lp",
> +static const struct console_operations lp_cons_ops = {
> .write = lp_console_write,
> - .flags = CON_PRINTBUFFER,
> };
>
> +static struct console *lpcons;
I have got the following compilation error (see below):
CC drivers/char/lp.o
drivers/char/lp.c: In function ‘lp_register’:
drivers/char/lp.c:925:2: error: ‘lpcons’ undeclared (first use in this function)
lpcons = allocate_console_dfl(&lp_cons_ops, "lp", NULL);
^
drivers/char/lp.c:925:2: note: each undeclared identifier is reported only once for each function it appears in
In file included from drivers/char/lp.c:125:0:
drivers/char/lp.c:925:33: error: ‘lp_cons_ops’ undeclared (first use in this function)
> #endif /* console on line printer */
>
> /* --- initialisation code ------------------------------------- */
> @@ -921,6 +921,11 @@ static int lp_register(int nr, struct parport *port)
> &ppdev_cb, nr);
> if (lp_table[nr].dev == NULL)
> return 1;
> +
> + lpcons = allocate_console_dfl(&lp_cons_ops, "lp", NULL);
> + if (!lpcons)
> + return -ENOMEM;
This should be done inside #ifdef CONFIG_LP_CONSOLE
to avoid the above compilation error.
> +
> lp_table[nr].flags |= LP_EXIST;
>
> if (reset)
[...]
> diff --git a/include/linux/console.h b/include/linux/console.h
> index 3c27a4a29b8c..382591683033 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -142,20 +143,28 @@ static inline int con_debug_leave(void)
> #define CON_BRL (32) /* Used for a braille device */
> #define CON_EXTENDED (64) /* Use the extended output format a la /dev/kmsg */
>
> -struct console {
> - char name[16];
> +struct console;
> +
> +struct console_operations {
> void (*write)(struct console *, const char *, unsigned);
> int (*read)(struct console *, char *, unsigned);
> struct tty_driver *(*device)(struct console *, int *);
> void (*unblank)(void);
> int (*setup)(struct console *, char *);
> int (*match)(struct console *, char *name, int idx, char *options);
> +};
> +
> +struct console {
> + char name[16];
> short flags;
> short index;
> int cflag;
> void *data;
> struct console *next;
> int level;
> + const struct console_operations *ops;
> + struct device dev;
> + int is_static;
> };
>
> /*
> @@ -167,6 +176,29 @@ struct console {
> extern int console_set_on_cmdline;
> extern struct console *early_console;
>
> +extern struct console *allocate_console(const struct console_operations *ops,
> + const char *name, short flags,
> + short index, void *data);
> +
> +#define allocate_console_dfl(ops, name, data) \
> + allocate_console(ops, name, CON_PRINTBUFFER, -1, data)
> +
> +/*
> + * Helpers for get/put that do the right thing for static early consoles.
> + */
> +
> +#define get_console(con) \
> +do { \
> + if (!con->is_static) \
> + get_device(&(con)->dev); \
> +} while (0)
> +
> +#define put_console(con) \
> +do { \
> + if (con && !con->is_static) \
> + put_device(&((struct console *)con)->dev); \
> +} while (0)
> +
> extern int add_preferred_console(char *name, int idx, char *options);
> extern void register_console(struct console *);
> extern int unregister_console(struct console *);
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 5fe2b037e833..29b43c4df3d6 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -426,6 +426,25 @@ int uart_add_one_port(struct uart_driver *reg, struct uart_port *port);
> int uart_remove_one_port(struct uart_driver *reg, struct uart_port *port);
> int uart_match_port(struct uart_port *port1, struct uart_port *port2);
>
> +/*
> + * This ugliness removes the need for #ifdef boilerplate in UART drivers which
> + * allow their console functionality to be disabled via Kconfig.
> + */
> +#define uart_allocate_console(drv, ops, name, flags, idx, kcfg) \
> +({ \
> + int __retval = 0; \
> + if (IS_ENABLED(CONFIG_##kcfg)) { \
I wonder if it is worth it. I do not see much existing #ifdef's
removed by this patch. I would expect that the code is never
called when the driver is disabled in Kconfig.
IMHO, such a trick hidden in a macro could cause more confusion
than good.
> + (drv)->cons = allocate_console(ops, name, flags, idx, drv); \
> + __retval = (drv)->cons ? 0 : -ENOMEM; \
> + } \
> + __retval; \
> +})
> +
> +#define uart_allocate_console_dfl(drv, ops, name, kcfg) \
> + uart_allocate_console(drv, ops, name, CON_PRINTBUFFER, -1, kcfg)
> +
> +#define uart_put_console(drv) put_console((drv)->cons)
> +
> /*
> * Power Management
> */
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 2e0eb89f046c..67e1e993ab80 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -108,6 +108,8 @@ enum devkmsg_log_masks {
>
> static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
>
> +static int printk_late_done;
> +
> static int __control_devkmsg(char *str)
> {
> if (!str)
> @@ -1731,7 +1733,7 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
> continue;
> if (!(con->flags & CON_ENABLED))
> continue;
> - if (!con->write)
> + if (!con->ops->write)
> continue;
> if (!cpu_online(smp_processor_id()) &&
> !(con->flags & CON_ANYTIME))
> @@ -1739,9 +1741,9 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
> if (suppress_message_printing(level, con))
> continue;
> if (con->flags & CON_EXTENDED)
> - con->write(con, ext_text, ext_len);
> + con->ops->write(con, ext_text, ext_len);
> else
> - con->write(con, text, len);
> + con->ops->write(con, text, len);
> }
> }
>
> @@ -2052,7 +2054,7 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
> n = vscnprintf(buf, sizeof(buf), fmt, ap);
> va_end(ap);
>
> - early_console->write(early_console, buf, n);
> + early_console->ops->write(early_console, buf, n);
> }
> #endif
>
> @@ -2481,8 +2483,8 @@ void console_unblank(void)
> console_locked = 1;
> console_may_schedule = 0;
> for_each_console(c)
> - if ((c->flags & CON_ENABLED) && c->unblank)
> - c->unblank();
> + if ((c->flags & CON_ENABLED) && c->ops->unblank)
> + c->ops->unblank();
> console_unlock();
> }
>
> @@ -2515,9 +2517,9 @@ struct tty_driver *console_device(int *index)
>
> console_lock();
> for_each_console(c) {
> - if (!c->device)
> + if (!c->ops->device)
> continue;
> - driver = c->device(c, index);
> + driver = c->ops->device(c, index);
> if (driver)
> break;
> }
> @@ -2558,6 +2560,68 @@ static int __init keep_bootcon_setup(char *str)
>
> early_param("keep_bootcon", keep_bootcon_setup);
>
> +static struct bus_type console_subsys = {
> + .name = "console",
> +};
> +
> +static void console_release(struct device *dev)
> +{
> + struct console *con = container_of(dev, struct console, dev);
> +
> + if (WARN(con->is_static, "Freeing static early console!\n"))
> + return;
> +
> + if (WARN(con->flags & CON_ENABLED, "Freeing running console!\n"))
> + return;
> +
> + pr_info("Freeing console %s\n", con->name);
> + kfree(con);
> +}
> +
> +static void console_init_device(struct console *con)
> +{
> + device_initialize(&con->dev);
> + dev_set_name(&con->dev, "%s", con->name);
> + con->dev.release = console_release;
> +}
> +
> +static void console_register_device(struct console *new)
> +{
> + /*
> + * We might be called very early from register_console(): in that case,
> + * printk_late_init() will take care of this later.
> + */
> + if (!printk_late_done)
> + return;
> +
> + if (new->is_static)
> + console_init_device(new);
> +
> + new->dev.bus = &console_subsys;
> + WARN_ON(device_add(&new->dev));
> +}
> +
> +struct console *allocate_console(const struct console_operations *ops,
> + const char *name, short flags, short index,
> + void *data)
> +{
> + struct console *new;
> +
> + new = kzalloc(sizeof(*new), GFP_KERNEL);
I have just realized that page_alloc_init() is called before
parse_early_param(). Therefore we should be able to use
memblock_alloc() for early consoles and reduce problems
with static structures.
> + if (!new)
> + return NULL;
> +
> + new->ops = ops;
> + strscpy(new->name, name, sizeof(new->name));
> + new->flags = flags;
> + new->index = index;
> + new->data = data;
> +
> + console_init_device(new);
This is a side effect that I would not expect from a function called
alloc*(). I would rename:
s/allocate_console/create_console/ or
s/allocate_console/init_console/
> + return new;
> +}
> +EXPORT_SYMBOL_GPL(allocate_console);
> +
> /*
> * The console driver calls this routine during kernel initialization
> * to register the console printing procedure with printk() and to
> @@ -2622,10 +2686,10 @@ void register_console(struct console *newcon)
> if (!has_preferred) {
> if (newcon->index < 0)
> newcon->index = 0;
> - if (newcon->setup == NULL ||
> - newcon->setup(newcon, NULL) == 0) {
> + if (newcon->ops->setup == NULL ||
> + newcon->ops->setup(newcon, NULL) == 0) {
> newcon->flags |= CON_ENABLED;
> - if (newcon->device) {
> + if (newcon->ops->device) {
There might be confusion why we need two devices (con->dev
and con->ops->device).
I would rename con->ops->device to con->ops->tty_dev.
> newcon->flags |= CON_CONSDEV;
> has_preferred = true;
> }
> @@ -2639,8 +2703,8 @@ void register_console(struct console *newcon)
> for (i = 0, c = console_cmdline;
> i < MAX_CMDLINECONSOLES && c->name[0];
> i++, c++) {
> - if (!newcon->match ||
> - newcon->match(newcon, c->name, c->index, c->options) != 0) {
> + if (!newcon->ops->match ||
> + newcon->ops->match(newcon, c->name, c->index, c->options) != 0) {
> /* default matching */
> BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
> if (strcmp(c->name, newcon->name) != 0)
> @@ -2660,8 +2724,8 @@ void register_console(struct console *newcon)
> if (_braille_register_console(newcon, c))
> return;
>
> - if (newcon->setup &&
> - newcon->setup(newcon, c->options) != 0)
> + if (newcon->ops->setup &&
> + newcon->ops->setup(newcon, c->options) != 0)
> break;
> }
>
> @@ -2706,6 +2770,8 @@ void register_console(struct console *newcon)
> console_drivers->next = newcon;
> }
>
> + get_console(newcon);
> +
> if (newcon->flags & CON_EXTENDED)
> nr_ext_console_drivers++;
>
> @@ -2730,6 +2796,7 @@ void register_console(struct console *newcon)
> exclusive_console_stop_seq = console_seq;
> logbuf_unlock_irqrestore(flags);
> }
> + console_register_device(newcon);
This calls console_init_device() for the statically defined
early consoles. I guess that it would invalidate the above
get_console().
Also it is not symmetric with unregister_console(). We add it
to the console_subsys here and did not remove it when
the console is unregistered.
IMHO, this might be done already in allocate_console().
And eventually in printk_late_init() for consoles that
are allocated earlier.
I am not familiar with the device-related sysfs API.
But I see that device_initialize() and device_add()
can be done by device_register(). The separate
calls are needed only when a special reference
handling is needed. Are we special?
Anyway, please, try to describe the expected workflow
in the commit description:
+ where the structure should get allocated
+ when it is added to the sysfs hierarchy
+ what happens when the console gets registered
and unregistered
+ when it is removed from the sysfs hierarchy
+ when the structure is released/freed
+ What is needed to get the console registered
and unregistered repeatedly on a running system
Finally, we might want to show state of the CON_ENABLED flag
in sysfs to distinguish the currently used consoles.
> console_unlock();
> console_sysfs_notify();
Thanks a lot for working on this. I know that it is not easy.
But it is really appreciated.
Best Regards,
Petr
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