cyber_file: enable large-chunk CYBER readsv42.1337.666

Allowing for reading CYBER in much larger chunks boosts read perfomance
on the Designated CYBER Test System (DCTS) from 4.2 Gibibyte per second
to 6.66 Gibibyte per second. All hail CYBER!

1 files changed, 11 insertions, 4 deletions

diff --git a/src/cyber_file.c b/src/cyber_file.c
index d7264c1..deaed39 100644
--- a/src/cyber_file.c
+++ b/src/cyber_file.c
@@ -39,12 +39,19 @@ int cyber_file_open(struct inode * inode, struct file * file)
 
 ssize_t cyber_file_read(struct file * file, char __user * buffer, size_t size, loff_t * offset)
 {
-	int const cybers = (size > PAGE_SIZE ? PAGE_SIZE : size) / 8;
-	if(copy_to_user(buffer, cyberSpace, cybers * 8))
+	int const cyberChunks = (size + PAGE_SIZE - 1) / PAGE_SIZE;
+	int const cybersPerChunk = (size > PAGE_SIZE ? PAGE_SIZE : size) / 8;
+	int remainingChunks = cyberChunks;
+
+	for(; remainingChunks > 0; --remainingChunks)
 	{
-		return -EFAULT;
+		if(copy_to_user(buffer, cyberSpace, cybersPerChunk * 8))
+		{
+			return -EFAULT;
+		}
 	}
-	return cybers * 8;
+
+	return cyberChunks * cybersPerChunk * 8;
 }
 
 ssize_t cyber_file_write(struct file * file, char __user const * buffer, size_t size, loff_t * offset)