mm/circbuf: add circ_peekat to read data with specified postion

Signed-off-by: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>

include/nuttx/mm/circbuf.h

@@ -198,11 +198,35 @@ size_t circbuf_used(FAR struct circbuf_s *circ);
 
 size_t circbuf_space(FAR struct circbuf_s *circ);
 
+/****************************************************************************
+ * Name: circbuf_peekat
+ *
+ * Description:
+ *   Get data speicified position from the circular buffer without removing
+ *
+ * Note :
+ *   That with only one concurrent reader and one concurrent writer,
+ *   you don't need extra locking to use these api.
+ *
+ * Input Parameters:
+ *   circ  - Address of the circular buffer to be used.
+ *   pos   - Position to read.
+ *   dst   - Address where to store the data.
+ *   bytes - Number of bytes to get.
+ *
+ * Returned Value:
+ *   The bytes of get data is returned if the peek data is successful;
+ *   A negated errno value is returned on any failure.
+ ****************************************************************************/
+
+ssize_t circbuf_peekat(FAR struct circbuf_s *circ, size_t pos,
+                       FAR void *dst, size_t bytes);
+
 /****************************************************************************
  * Name: circbuf_peek
  *
  * Description:
- *   Get data form the circular buffer without removing
+ *   Get data from the circular buffer without removing
  *
  * Note :
  *   That with only one concurrent reader and one concurrent writer,
@@ -225,7 +249,7 @@ ssize_t circbuf_peek(FAR struct circbuf_s *circ,
  * Name: circbuf_read
  *
  * Description:
- *   Get data form the circular buffer.
+ *   Get data from the circular buffer.
  *
  * Note :
  *   That with only one concurrent reader and one concurrent writer,
@@ -248,7 +272,7 @@ ssize_t circbuf_read(FAR struct circbuf_s *circ,
  * Name: circbuf_skip
  *
  * Description:
- *   Skip data form the circular buffer.
+ *   Skip data from the circular buffer.
  *
  * Note:
  *   That with only one concurrent reader and one concurrent writer,

mm/circbuf/circbuf.c

@@ -273,10 +273,10 @@ bool circbuf_is_full(FAR struct circbuf_s *circ)
 }
 
 /****************************************************************************
- * Name: circbuf_peek
+ * Name: circbuf_peekat
  *
  * Description:
- *   Get data form the circular buffer without removing
+ *   Get data speicified position from the circular buffer without removing
  *
  * Note :
  *   That with only one concurrent reader and one concurrent writer,
@@ -284,6 +284,7 @@ bool circbuf_is_full(FAR struct circbuf_s *circ)
  *
  * Input Parameters:
  *   circ  - Address of the circular buffer to be used.
+ *   pos   - Position to read.
  *   dst   - Address where to store the data.
  *   bytes - Number of bytes to get.
  *
@@ -292,8 +293,8 @@ bool circbuf_is_full(FAR struct circbuf_s *circ)
  *   A negated errno value is returned on any failure.
  ****************************************************************************/
 
-ssize_t circbuf_peek(FAR struct circbuf_s *circ,
-                      FAR void *dst, size_t bytes)
+ssize_t circbuf_peekat(FAR struct circbuf_s *circ, size_t pos,
+                       FAR void *dst, size_t bytes)
 {
   size_t len;
   size_t off;
@@ -306,7 +307,7 @@ ssize_t circbuf_peek(FAR struct circbuf_s *circ,
     }
 
   len = circbuf_used(circ);
-  off = circ->tail % circ->size;
+  off = pos % circ->size;
 
   if (bytes > len)
     {
@@ -325,11 +326,37 @@ ssize_t circbuf_peek(FAR struct circbuf_s *circ,
   return bytes;
 }
 
+/****************************************************************************
+ * Name: circbuf_peek
+ *
+ * Description:
+ *   Get data from the circular buffer without removing
+ *
+ * Note :
+ *   That with only one concurrent reader and one concurrent writer,
+ *   you don't need extra locking to use these api.
+ *
+ * Input Parameters:
+ *   circ  - Address of the circular buffer to be used.
+ *   dst   - Address where to store the data.
+ *   bytes - Number of bytes to get.
+ *
+ * Returned Value:
+ *   The bytes of get data is returned if the peek data is successful;
+ *   A negated errno value is returned on any failure.
+ ****************************************************************************/
+
+ssize_t circbuf_peek(FAR struct circbuf_s *circ,
+                     FAR void *dst, size_t bytes)
+{
+  return circbuf_peekat(circ, circ->tail, dst, bytes);
+}
+
 /****************************************************************************
  * Name: circbuf_read
  *
  * Description:
- *   Get data form the circular buffer.
+ *   Get data from the circular buffer.
  *
  * Note :
  *   That with only one concurrent reader and one concurrent writer,
@@ -346,7 +373,7 @@ ssize_t circbuf_peek(FAR struct circbuf_s *circ,
  ****************************************************************************/
 
 ssize_t circbuf_read(FAR struct circbuf_s *circ,
-                      FAR void *dst, size_t bytes)
+                     FAR void *dst, size_t bytes)
 {
   DEBUGASSERT(circ);
   DEBUGASSERT(dst || !bytes);
@@ -361,7 +388,7 @@ ssize_t circbuf_read(FAR struct circbuf_s *circ,
  * Name: circbuf_skip
  *
  * Description:
- *   Skip data form the circular buffer.
+ *   Skip data from the circular buffer.
  *
  * Note :
  *   That with only one concurrent reader and one concurrent writer,
@@ -415,7 +442,7 @@ ssize_t circbuf_skip(FAR struct circbuf_s *circ, size_t bytes)
  ****************************************************************************/
 
 ssize_t circbuf_write(FAR struct circbuf_s *circ,
-                       FAR const void *src, size_t bytes)
+                      FAR const void *src, size_t bytes)
 {
   size_t space;
   size_t off;
@@ -471,7 +498,7 @@ ssize_t circbuf_write(FAR struct circbuf_s *circ,
  ****************************************************************************/
 
 ssize_t circbuf_overwrite(FAR struct circbuf_s *circ,
-                           FAR const void *src, size_t bytes)
+                          FAR const void *src, size_t bytes)
 {
   size_t overwrite = 0;
   size_t space;