[PATCH printk v2 5/7] printk: Use struct console_buffers

John Ogness
2022-11-23T23:14:37Z

From: Thomas Gleixner <tglx@linutronix.de>

Replace the separately allocated output buffers with a single
instance of struct console_buffers.

Note that the buffer size of devkmsg_user.text_buf, when replaced
with console_buffers.text, reduces from CONSOLE_EXT_LOG_MAX to
CONSOLE_LOG_MAX. However, the buffer is only used to read ringbuffer
records. These records have a maximum size of LOG_LINE_MAX, which
is defined as CONSOLE_LOG_MAX - PREFIX_MAX.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 68 ++++++++++++++++++++----------------------
1 file changed, 32 insertions(+), 36 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a4854a60e6d8..750559171e30 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -712,11 +712,9 @@ struct devkmsg_user {
atomic64_t seq;
struct ratelimit_state rs;
struct mutex lock;
- char buf[CONSOLE_EXT_LOG_MAX];
-
struct printk_info info;
- char text_buf[CONSOLE_EXT_LOG_MAX];
struct printk_record record;
+ struct console_buffers cbufs;
};

static __printf(3, 4) __cold
@@ -798,6 +796,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
struct devkmsg_user *user = file->private_data;
+ const int ext_text_size = sizeof(user->cbufs.ext_text);
+ char *ext_text = &user->cbufs.ext_text[0];
struct printk_record *r = &user->record;
size_t len;
ssize_t ret;
@@ -839,8 +839,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
goto out;
}

- len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
- len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
+ len = info_print_ext_header(ext_text, ext_text_size, r->info);
+ len += msg_print_ext_body(ext_text + len, ext_text_size - len,
&r->text_buf[0], r->info->text_len,
&r->info->dev_info);

@@ -851,7 +851,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
goto out;
}

- if (copy_to_user(buf, user->buf, len)) {
+ if (copy_to_user(buf, ext_text, len)) {
ret = -EFAULT;
goto out;
}
@@ -950,7 +950,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
mutex_init(&user->lock);

prb_rec_init_rd(&user->record, &user->info,
- &user->text_buf[0], sizeof(user->text_buf));
+ &user->cbufs.text[0], sizeof(user->cbufs.text));

atomic64_set(&user->seq, prb_first_valid_seq(prb));

@@ -2007,6 +2007,10 @@ static int console_trylock_spinning(void)
return 1;
}

+#if DROPPED_TEXT_MAX > CONSOLE_EXT_LOG_MAX
+#error "DROPPED_TEXT_MAX too large for console_buffers->ext_text"
+#endif
+
/*
* Call the specified console driver, asking it to write out the specified
* text and length. If @dropped_text is non-NULL and any records have been
@@ -2741,36 +2745,32 @@ static void __console_unlock(void)
* Print one record for the given console. The record printed is whatever
* record is the next available record for the given console.
*
- * @text is a buffer of size CONSOLE_LOG_MAX.
+ * @cbufs is the console buffers used to string-print the formatted messages.
*
- * If extended messages should be printed, @ext_text is a buffer of size
- * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
- *
- * If dropped messages should be printed, @dropped_text is a buffer of size
- * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
+ * @cookie is the cookie from entering the SRCU read-side critical section.
*
* @handover will be set to true if a printk waiter has taken over the
* console_lock, in which case the caller is no longer holding both the
* console_lock and the SRCU read lock. Otherwise it is set to false.
*
- * @cookie is the cookie from the SRCU read lock.
- *
* Returns false if the given console has no next record to print, otherwise
* true.
*
* Requires the console_lock and the SRCU read lock.
*/
-static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
- char *dropped_text, bool *handover, int cookie)
+static bool console_emit_next_record(struct console *con, struct console_buffers *cbufs,
+ int cookie, bool *handover)
{
static int panic_console_dropped;
struct printk_info info;
struct printk_record r;
+ size_t write_text_size;
unsigned long flags;
+ char *dropped_text;
char *write_text;
size_t len;

- prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
+ prb_rec_init_rd(&r, &info, &cbufs->text[0], sizeof(cbufs->text));

*handover = false;

@@ -2792,13 +2792,20 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
goto skip;
}

- if (ext_text) {
- write_text = ext_text;
- len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
- len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
+ if (console_srcu_read_flags(con) & CON_EXTENDED) {
+ /* Extended consoles do not print "dropped messages". */
+ dropped_text = NULL;
+
+ write_text = &cbufs->ext_text[0];
+ write_text_size = sizeof(cbufs->ext_text);
+ len = info_print_ext_header(write_text, write_text_size, r.info);
+ len += msg_print_ext_body(write_text + len, write_text_size - len,
&r.text_buf[0], r.info->text_len, &r.info->dev_info);
} else {
- write_text = text;
+ /* @ext_text is unused. Use it for "dropped messages". */
+ dropped_text = &cbufs->ext_text[0];
+
+ write_text = &cbufs->text[0];
len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
}

@@ -2852,9 +2859,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
*/
static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
{
- static char dropped_text[DROPPED_TEXT_MAX];
- static char ext_text[CONSOLE_EXT_LOG_MAX];
- static char text[CONSOLE_LOG_MAX];
+ static struct console_buffers cbufs;
bool any_usable = false;
struct console *con;
bool any_progress;
@@ -2874,16 +2879,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
continue;
any_usable = true;

- if (console_srcu_read_flags(con) & CON_EXTENDED) {
- /* Extended consoles do not print "dropped messages". */
- progress = console_emit_next_record(con, &text[0],
- &ext_text[0], NULL,
- handover, cookie);
- } else {
- progress = console_emit_next_record(con, &text[0],
- NULL, &dropped_text[0],
- handover, cookie);
- }
+ progress = console_emit_next_record(con, &cbufs, cookie, handover);

/*
* If a handover has occurred, the SRCU read lock
--
2.30.2