fs/inode: improve the performance of get file pointer

After entering the critical section, we can access the
file pointer without locking the file list directly.
This is safe since the array access will not cause scheduling switching.

Signed-off-by: chao an <[email protected]>

fs/inode/fs_files.c

@@ -68,6 +68,7 @@ static FAR struct file *files_fget(int fd, FAR struct filelist *list)
 static int files_extend(FAR struct filelist *list, size_t row)
 {
   FAR struct file **tmp;
+  irqstate_t flags;
   int i;
 
   if (row <= list->fl_rows)
@@ -80,7 +81,7 @@ static int files_extend(FAR struct filelist *list, size_t row)
       return -EMFILE;
     }
 
-  tmp = kmm_realloc(list->fl_files, sizeof(FAR struct file *) * row);
+  tmp = kmm_malloc(sizeof(FAR struct file *) * row);
   DEBUGASSERT(tmp);
   if (tmp == NULL)
     {
@@ -105,9 +106,16 @@ static int files_extend(FAR struct filelist *list, size_t row)
     }
   while (++i < row);
 
+  flags = enter_critical_section();
+
+  memcpy(tmp, list->fl_files,
+         list->fl_rows * sizeof(FAR struct file *));
+
   list->fl_files = tmp;
   list->fl_rows = row;
 
+  leave_critical_section(flags);
+
   /* Note: If assertion occurs, the fl_rows has a overflow.
    * And there may be file descriptors leak in system.
    */
@@ -594,26 +602,42 @@ int fs_getfilep(int fd, FAR struct file **filep)
    * thread-specific file list.
    */
 
-  /* And return the file pointer from the list */
-
-  ret = nxmutex_lock(&list->fl_lock);
-  if (ret < 0)
+  if (!nxmutex_is_locked(&list->fl_lock))
     {
-      leave_critical_section(flags);
-      return ret;
+      *filep = files_fget(fd, list);
+
+      /* if f_inode is NULL, fd was closed */
+
+      if (!(*filep)->f_inode)
+        {
+          *filep = NULL;
+          ret = -EBADF;
+        }
     }
+  else
+    {
+      /* And return the file pointer from the list */
 
-  *filep = files_fget(fd, list);
+      ret = nxmutex_lock(&list->fl_lock);
+      if (ret < 0)
+        {
+          leave_critical_section(flags);
+          return ret;
+        }
 
-  /* if f_inode is NULL, fd was closed */
+      *filep = files_fget(fd, list);
 
-  if (!(*filep)->f_inode)
-    {
-      *filep = NULL;
-      ret = -EBADF;
+      /* if f_inode is NULL, fd was closed */
+
+      if (!(*filep)->f_inode)
+        {
+          *filep = NULL;
+          ret = -EBADF;
+        }
+
+      nxmutex_unlock(&list->fl_lock);
     }
 
-  nxmutex_unlock(&list->fl_lock);
   leave_critical_section(flags);
   return ret;
 }