[PATCH printk-rework 04/14] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code

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

The logic for finding records to fit into a buffer is the same for
kmsg_dump_get_buffer() and syslog_print_all(). Introduce a helper
function find_first_fitting_seq() to handle this logic.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 87 ++++++++++++++++++++++++------------------
1 file changed, 50 insertions(+), 37 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index b4f72b5f70b9..d6f93ebd7bd0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1422,6 +1422,50 @@ static size_t get_record_print_text_size(struct printk_info *info,
return ((prefix_len * line_count) + info->text_len + 1);
}

+/*
+ * Beginning with @start_seq, find the first record where it and all following
+ * records up to (but not including) @max_seq fit into @size.
+ *
+ * @max_seq is simply an upper bound and does not need to exist. If the caller
+ * does not require an upper bound, -1 can be used for @max_seq.
+ */
+static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
+ bool syslog, bool time)
+{
+ struct printk_info info;
+ unsigned int line_count;
+ size_t len = 0;
+ u64 seq;
+
+ /* Determine the size of the records up to @max_seq. */
+ prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+ if (info.seq >= max_seq)
+ break;
+ len += get_record_print_text_size(&info, line_count, syslog, time);
+ }
+
+ /*
+ * Adjust the upper bound for the next loop to avoid subtracting
+ * lengths that were never added.
+ */
+ if (seq < max_seq)
+ max_seq = 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 a best effort
+ * that prevents an infinite loop that could occur with a retry.
+ */
+ prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+ if (len <= size || info.seq >= max_seq)
+ break;
+ len -= get_record_print_text_size(&info, line_count, syslog, time);
+ }
+
+ return seq;
+}
+
static int syslog_print(char __user *buf, int size)
{
struct printk_info info;
@@ -1493,9 +1537,7 @@ static int syslog_print(char __user *buf, int size)
static int syslog_print_all(char __user *buf, int size, bool clear)
{
struct printk_info info;
- unsigned int line_count;
struct printk_record r;
- u64 max_seq;
char *text;
int len = 0;
u64 seq;
@@ -1511,21 +1553,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
* Find first record that fits, including all following records,
* into the user-provided buffer for this dump.
*/
- prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
- len += get_record_print_text_size(&info, line_count, true, time);
-
- /*
- * Set an upper bound for the next loop to avoid subtracting lengths
- * that were never added.
- */
- max_seq = seq;
-
- /* move first record forward until length fits into the buffer */
- prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
- if (len <= size || info.seq >= max_seq)
- break;
- len -= get_record_print_text_size(&info, line_count, true, time);
- }
+ seq = find_first_fitting_seq(clear_seq, -1, size, true, time);

prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);

@@ -3423,7 +3451,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
char *buf, size_t size, size_t *len_out)
{
struct printk_info info;
- unsigned int line_count;
struct printk_record r;
unsigned long flags;
u64 seq;
@@ -3451,26 +3478,12 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,

/*
* Find first record that fits, including all following records,
- * into the user-provided buffer for this dump.
+ * into the user-provided buffer for this dump. Pass in size-1
+ * because this function (by way of record_print_text()) will
+ * not write more than size-1 bytes of text into @buf.
*/
-
- prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
- if (info.seq >= dumper->next_seq)
- break;
- len += get_record_print_text_size(&info, line_count, syslog, time);
- }
-
- /*
- * 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;
- len -= get_record_print_text_size(&info, line_count, syslog, time);
- }
+ seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+ size - 1, syslog, time);

/*
* Next kmsg_dump_get_buffer() invocation will dump block of
--
2.20.1