st.ko: fix enlarge_buffer

From: Bodo Stroesser <[email protected]>
Date: Mon, 2 Dec 2013 18:52:10 +0100
Subject: [PATCH 1/3] st.ko: fix enlarge_buffer

This patch removes a bug in enlarge_buffer() that can make a read or write fail under special conditions.

After changing TRY_DIRECT_IO to 0 and ST_MAX_SG to 32 in st_options.h, a program that writes a first block of 128k and than a second bigger block (e.g. 256k) fails. The second write returns errno EOVERFLOW, as enlarge_buffer() checks the sg list and detects that it already is full.
As enlarge_buffer uses different page allocation orders depending on the size of the buffer needed, the check does not make sense.

---

@@ -3719,7 +3719,7 @@ static struct st_buffer *new_tape_buffer
 
 static int enlarge_buffer(struct st_buffer * STbuffer, int new_size, int need_dma)
 {
-	int segs, nbr, max_segs, b_size, order, got;
+	int segs, max_segs, b_size, order, got;
 	gfp_t priority;
 
 	if (new_size <= STbuffer->buffer_size)

@@ -3729,9 +3729,6 @@ static int enlarge_buffer(struct st_buff
 		normalize_buffer(STbuffer);  /* Avoid extra segment */
 
 	max_segs = STbuffer->use_sg;
-	nbr = max_segs - STbuffer->frp_segs;
-	if (nbr <= 0)
-		return 0;
 
 	priority = GFP_KERNEL | __GFP_NOWARN;
 	if (need_dma)