printk: refactor kmsg_dump_get_buffer()

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>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210303101528.29901-6-john.ogness@linutronix.de

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index ae38035f1dca97c970a4d21c06e5baa3d9243e94..070c994ff19fa8da1e1eab8b8353269141a1da82 100644 (file)
--- 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 77ae2704e979cd4d2e12174db6965eadadbd2338..ed678d84dc51c7a47fae03ba9569f1ca668e30e9 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3410,7 +3410,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
- * @len: length of line placed into buffer
+ * @len_out: length of line placed into buffer
  *
  * Start at the end of the kmsg buffer and fill the provided buffer
  * with as many of the *youngest* kmsg records that fit into it.
@@ -3424,7 +3424,7 @@ 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;
@@ -3432,12 +3432,10 @@ 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;
 
@@ -3455,48 +3453,54 @@ 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);
+               len += record_print_text(&r, syslog, time);
 
-               /* adjust record to store to remaining buffer space */
-               prb_rec_init_rd(&r, &info, buf + l, size - l);
-
-               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);