[PATCH printk-rework 03/14] printk: refactor kmsg_dump_get_buffer()

John Ogness
2021-02-18T09:40:03Z

kmsg_dump_get_buffer() requires nearly the same logic as
syslog_print_all(), but uses different variable names and
does not make use of the ringbuffer loop macros. Modify
kmsg_dump_get_buffer() so that the implementation is as similar
to syslog_print_all() as possible.

A follow-up commit will move this common logic into a
separate helper function.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
include/linux/kmsg_dump.h | 2 +-
kernel/printk/printk.c | 60 +++++++++++++++++++++------------------
2 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 235c50982c2d..4095a34db0fa 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -62,7 +62,7 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
char *line, size_t size, size_t *len);

bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
- char *buf, size_t size, size_t *len);
+ char *buf, size_t size, size_t *len_out);

void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 411787b900ac..b4f72b5f70b9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3420,7 +3420,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
* read.
*/
bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
- char *buf, size_t size, size_t *len)
+ char *buf, size_t size, size_t *len_out)
{
struct printk_info info;
unsigned int line_count;
@@ -3428,12 +3428,10 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
unsigned long flags;
u64 seq;
u64 next_seq;
- size_t l = 0;
+ size_t len = 0;
bool ret = false;
bool time = printk_time;

- prb_rec_init_rd(&r, &info, buf, size);
-
if (!dumper->active || !buf || !size)
goto out;

@@ -3451,48 +3449,54 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
goto out;
}

- /* calculate length of entire buffer */
- seq = dumper->cur_seq;
- while (prb_read_valid_info(prb, seq, &info, &line_count)) {
- if (r.info->seq >= dumper->next_seq)
+ /*
+ * Find first record that fits, including all following records,
+ * into the user-provided buffer for this dump.
+ */
+
+ prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
+ if (info.seq >= dumper->next_seq)
break;
- l += get_record_print_text_size(&info, line_count, syslog, time);
- seq = r.info->seq + 1;
+ len += get_record_print_text_size(&info, line_count, syslog, time);
}

- /* move first record forward until length fits into the buffer */
- seq = dumper->cur_seq;
- while (l >= size && prb_read_valid_info(prb, seq,
- &info, &line_count)) {
- if (r.info->seq >= dumper->next_seq)
+ /*
+ * Move first record forward until length fits into the buffer. Ignore
+ * newest messages that were not counted in the above cycle. Messages
+ * might appear and get lost in the meantime. This is the best effort
+ * that prevents an infinite loop.
+ */
+ prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
+ if (len < size || info.seq >= dumper->next_seq)
break;
- l -= get_record_print_text_size(&info, line_count, syslog, time);
- seq = r.info->seq + 1;
+ len -= get_record_print_text_size(&info, line_count, syslog, time);
}

- /* last message in next interation */
+ /*
+ * Next kmsg_dump_get_buffer() invocation will dump block of
+ * older records stored right before this one.
+ */
next_seq = seq;

- /* actually read text into the buffer now */
- l = 0;
- while (prb_read_valid(prb, seq, &r)) {
+ prb_rec_init_rd(&r, &info, buf, size);
+
+ len = 0;
+ prb_for_each_record(seq, prb, seq, &r) {
if (r.info->seq >= dumper->next_seq)
break;

- l += record_print_text(&r, syslog, time);
-
- /* adjust record to store to remaining buffer space */
- prb_rec_init_rd(&r, &info, buf + l, size - l);
+ len += record_print_text(&r, syslog, time);

- seq = r.info->seq + 1;
+ /* Adjust record to store to remaining buffer space. */
+ prb_rec_init_rd(&r, &info, buf + len, size - len);
}

dumper->next_seq = next_seq;
ret = true;
logbuf_unlock_irqrestore(flags);
out:
- if (len)
- *len = l;
+ if (len_out)
+ *len_out = len;
return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
--
2.20.1