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Subject[RFC PATCH v1 21/25] printk: implement KERN_CONT
Date
Implement KERN_CONT based on the printing CPU rather than on the
printing task. As long as the KERN_CONT messages are coming from the
same CPU and no non-KERN_CONT messages come, the messages are assumed
to belong to each other.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 73 +++++++++++++++++++++++++++++---------------------
1 file changed, 42 insertions(+), 31 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index eebe6f4fdbba..306e7575499c 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1649,8 +1649,6 @@ static void call_console_drivers(u64 seq, const char *ext_text, size_t ext_len,
}
}

-/* FIXME: no support for LOG_CONT */
-#if 0
/*
* Continuation lines are buffered, and not committed to the record buffer
* until the line is complete, or a race forces it. The line fragments
@@ -1660,52 +1658,57 @@ static void call_console_drivers(u64 seq, const char *ext_text, size_t ext_len,
static struct cont {
char buf[LOG_LINE_MAX];
size_t len; /* length == 0 means unused buffer */
- struct task_struct *owner; /* task of first print*/
+ int cpu_owner; /* cpu of first print*/
u64 ts_nsec; /* time of first print */
u8 level; /* log level of first message */
u8 facility; /* log facility of first message */
enum log_flags flags; /* prefix, newline flags */
-} cont;
+} cont[2];

-static void cont_flush(void)
+static void cont_flush(int ctx)
{
- if (cont.len == 0)
+ struct cont *c = &cont[ctx];
+
+ if (c->len == 0)
return;

- log_store(cont.facility, cont.level, cont.flags, cont.ts_nsec,
- NULL, 0, cont.buf, cont.len);
- cont.len = 0;
+ log_store(c->facility, c->level, c->flags, c->ts_nsec, c->cpu_owner,
+ NULL, 0, c->buf, c->len);
+ c->len = 0;
}

-static bool cont_add(int facility, int level, enum log_flags flags, const char *text, size_t len)
+static void cont_add(int ctx, int cpu, int facility, int level,
+ enum log_flags flags, const char *text, size_t len)
{
+ struct cont *c = &cont[ctx];
+
+ if (cpu != c->cpu_owner || !(flags & LOG_CONT))
+ cont_flush(ctx);
+
/* If the line gets too long, split it up in separate records. */
- if (cont.len + len > sizeof(cont.buf)) {
- cont_flush();
- return false;
- }
+ while (c->len + len > sizeof(c->buf))
+ cont_flush(ctx);

- if (!cont.len) {
- cont.facility = facility;
- cont.level = level;
- cont.owner = current;
- cont.ts_nsec = local_clock();
- cont.flags = flags;
+ if (!c->len) {
+ c->facility = facility;
+ c->level = level;
+ c->cpu_owner = cpu;
+ c->ts_nsec = local_clock();
+ c->flags = flags;
}

- memcpy(cont.buf + cont.len, text, len);
- cont.len += len;
+ memcpy(c->buf + c->len, text, len);
+ c->len += len;

- // The original flags come from the first line,
- // but later continuations can add a newline.
+ /*
+ * The original flags come from the first line,
+ * but later continuations can add a newline.
+ */
if (flags & LOG_NEWLINE) {
- cont.flags |= LOG_NEWLINE;
- cont_flush();
+ c->flags |= LOG_NEWLINE;
+ cont_flush(ctx);
}
-
- return true;
}
-#endif /* 0 */

/* ring buffer used as memory allocator for temporary sprint buffers */
DECLARE_STATIC_PRINTKRB(sprint_rb,
@@ -1717,6 +1720,7 @@ asmlinkage int vprintk_emit(int facility, int level,
const char *fmt, va_list args)
{
enum log_flags lflags = 0;
+ int ctx = !!in_nmi();
int printed_len = 0;
struct prb_handle h;
size_t text_len;
@@ -1784,8 +1788,15 @@ asmlinkage int vprintk_emit(int facility, int level,
*/
printk_emergency(rbuf, level, ts_nsec, cpu, text, text_len);

- printed_len = log_store(facility, level, lflags, ts_nsec, cpu,
- dict, dictlen, text, text_len);
+ if ((lflags & LOG_CONT) || !(lflags & LOG_NEWLINE)) {
+ cont_add(ctx, cpu, facility, level, lflags, text, text_len);
+ printed_len = text_len;
+ } else {
+ if (cpu == cont[ctx].cpu_owner)
+ cont_flush(ctx);
+ printed_len = log_store(facility, level, lflags, ts_nsec, cpu,
+ dict, dictlen, text, text_len);
+ }

prb_commit(&h);
return printed_len;
--
2.11.0
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