From 880d78f903a7506cdcaa9de38b1e22b04ecb707b Mon Sep 17 00:00:00 2001
From: Fotis Panagiotopoulos <f.panag@amco.gr>
Date: Mon, 19 Jun 2023 18:33:17 +0300
Subject: [PATCH] sendfile: Fixed behavior of sendfile when count is set to
 zero.

If sendfile() is called with a zero count, it will nevertheless
try to send the data. This is mostly meaningless, it causes
waste of resources, and in some cases delays.

This commit adds special handling for this case, allowing
sendfile to return immediately zero. The new behavior is
in line with the Linux variant of sendfile.
---
 fs/vfs/fs_sendfile.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/vfs/fs_sendfile.c b/fs/vfs/fs_sendfile.c
index 5b4ec2cff5..ac460a63bf 100644
--- a/fs/vfs/fs_sendfile.c
+++ b/fs/vfs/fs_sendfile.c
@@ -27,6 +27,7 @@
 #include <sys/sendfile.h>
 #include <stdbool.h>
 #include <errno.h>
+#include <debug.h>
 
 #include <nuttx/kmalloc.h>
 #include <nuttx/net/net.h>
@@ -244,6 +245,12 @@ static ssize_t copyfile(FAR struct file *outfile, FAR struct file *infile,
 ssize_t file_sendfile(FAR struct file *outfile, FAR struct file *infile,
                       off_t *offset, size_t count)
 {
+  if (count == 0)
+    {
+      nwarn("WARNING: sendfile count is zero\n");
+      return 0;
+    }
+
 #ifdef CONFIG_NET_SENDFILE
   /* Check the destination file descriptor:  Is it a (probable) file
    * descriptor?  Check the source file:  Is it a normal file?