From a8866132c2ac2f7ca37e568bd062519b58a211a1 Mon Sep 17 00:00:00 2001
From: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>
Date: Mon, 28 Feb 2022 21:39:59 +0800
Subject: [PATCH] ramlog: support setting threshold value of ramlog for poll
 waiters

Signed-off-by: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>
---
 drivers/syslog/Kconfig  |  6 ++++++
 drivers/syslog/ramlog.c | 21 ++++++++++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/syslog/Kconfig b/drivers/syslog/Kconfig
index ccf65e56f8..9fd74e4e80 100644
--- a/drivers/syslog/Kconfig
+++ b/drivers/syslog/Kconfig
@@ -61,6 +61,12 @@ config RAMLOG_OVERWRITE
 		Enable overwrite of circular buffer. If RAMLOG buffer overflows,
 		overwrite it from the top of buffer and always keep the latest log.
 
+config RAMLOG_POLLTHRESHOLD
+	int "The threshold value of circular buffer to notify poll waiters"
+	default 1
+	---help---
+		When the length of circular buffer exceeds the threshold value, the poll() will
+		return POLLIN to all poll waiters.
 endif
 
 config SYSLOG_BUFFER
diff --git a/drivers/syslog/ramlog.c b/drivers/syslog/ramlog.c
index 880ab30671..55cca259bb 100644
--- a/drivers/syslog/ramlog.c
+++ b/drivers/syslog/ramlog.c
@@ -155,6 +155,16 @@ static struct ramlog_dev_s g_sysdev =
  * Private Functions
  ****************************************************************************/
 
+/****************************************************************************
+ * Name: ramlog_bufferused
+ ****************************************************************************/
+
+static size_t ramlog_bufferused(FAR struct ramlog_dev_s *priv)
+{
+  return (priv->rl_bufsize + priv->rl_head - priv->rl_tail) %
+         priv->rl_bufsize;
+}
+
 /****************************************************************************
  * Name: ramlog_readnotify
  ****************************************************************************/
@@ -408,7 +418,8 @@ static ssize_t ramlog_addbuf(FAR struct ramlog_dev_s *priv,
        * operations a critical section.
        */
 
-      if (readers_waken == 0)
+      if (readers_waken == 0 &&
+          ramlog_bufferused(priv) >= CONFIG_RAMLOG_POLLTHRESHOLD)
         {
           /* Notify all poll/select waiters that they can read from the
            * FIFO.
@@ -633,8 +644,7 @@ static int ramlog_file_ioctl(FAR struct file *filep, int cmd,
   switch (cmd)
     {
       case FIONREAD:
-        *(FAR int *)((uintptr_t)arg) = (priv->rl_bufsize + priv->rl_head -
-                                        priv->rl_tail) % priv->rl_bufsize;
+        *(FAR int *)((uintptr_t)arg) = ramlog_bufferused(priv);
         break;
       default:
         ret = -ENOTTY;
@@ -723,7 +733,7 @@ static int ramlog_file_poll(FAR struct file *filep, FAR struct pollfd *fds,
 
       /* Check if the receive buffer is not empty. */
 
-      if (priv->rl_head != priv->rl_tail)
+      if (ramlog_bufferused(priv) >= CONFIG_RAMLOG_POLLTHRESHOLD)
         {
           eventset |= POLLIN;
         }
@@ -874,7 +884,8 @@ int ramlog_putc(FAR struct syslog_channel_s *channel, int ch)
    * operations a critical section.
    */
 
-  if (readers_waken == 0)
+  if (readers_waken == 0 &&
+      ramlog_bufferused(priv) >= CONFIG_RAMLOG_POLLTHRESHOLD)
     {
       /* Notify all poll/select waiters that they can read from the FIFO */