linux-kernel - [PATCH 3/7] Drivers: hv: ring_buffer: use wrap around mappings in hv_copy{from,to}

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Message-Id: <1472821105-7150-3-git-send-email-kys@exchange.microsoft.com>
Date:   Fri,  2 Sep 2016 05:58:21 -0700
From:   kys@...hange.microsoft.com
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        vkuznets@...hat.com, jasowang@...hat.com,
        leann.ogasawara@...onical.com, alexng@...rosoft.com
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 3/7] Drivers: hv: ring_buffer: use wrap around mappings in hv_copy{from,to}_ringbuffer()

From: Vitaly Kuznetsov <vkuznets@...hat.com>

With wrap around mappings for ring buffers we can always use a single
memcpy() to do the job.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
Tested-by: Dexuan Cui <decui@...rosoft.com>
---
 drivers/hv/ring_buffer.c |   24 +++---------------------
 1 files changed, 3 insertions(+), 21 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 7e21c2c..08043da 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -172,18 +172,7 @@ static u32 hv_copyfrom_ringbuffer(
 	void *ring_buffer = hv_get_ring_buffer(ring_info);
 	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 
-	u32 frag_len;
-
-	/* wrap-around detected at the src */
-	if (destlen > ring_buffer_size - start_read_offset) {
-		frag_len = ring_buffer_size - start_read_offset;
-
-		memcpy(dest, ring_buffer + start_read_offset, frag_len);
-		memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
-	} else
-
-		memcpy(dest, ring_buffer + start_read_offset, destlen);
-
+	memcpy(dest, ring_buffer + start_read_offset, destlen);
 
 	start_read_offset += destlen;
 	start_read_offset %= ring_buffer_size;
@@ -204,15 +193,8 @@ static u32 hv_copyto_ringbuffer(
 {
 	void *ring_buffer = hv_get_ring_buffer(ring_info);
 	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
-	u32 frag_len;
-
-	/* wrap-around detected! */
-	if (srclen > ring_buffer_size - start_write_offset) {
-		frag_len = ring_buffer_size - start_write_offset;
-		memcpy(ring_buffer + start_write_offset, src, frag_len);
-		memcpy(ring_buffer, src + frag_len, srclen - frag_len);
-	} else
-		memcpy(ring_buffer + start_write_offset, src, srclen);
+
+	memcpy(ring_buffer + start_write_offset, src, srclen);
 
 	start_write_offset += srclen;
 	start_write_offset %= ring_buffer_size;
-- 
1.7.4.1