[PATCH] btrfs-progs: align btrfs receive buffer to enable fast CRC

[shngmao@gmail.com]

From: Sheng Mao <shngmao@gmail.com>

To use optimized CRC implemention, the input buffer must be
unsigned long aligned. btrfs receive calculates checksum based on
read_buf, including btrfs_cmd_header (with zero-ed CRC field)
and command content. GCC attribute is added to both struct
btrfs_send_stream and read_buf to make sure read_buf is allocated
with proper alignment.

Issue: #324
Signed-off-by: Sheng Mao <shngmao@gmail.com>
---
 common/send-stream.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/common/send-stream.c b/common/send-stream.c
index 69d75168..b13aa16e 100644
--- a/common/send-stream.c
+++ b/common/send-stream.c
@@ -26,7 +26,8 @@
 
 struct btrfs_send_stream {
 	int fd;
-	char read_buf[BTRFS_SEND_BUF_SIZE];
+	char read_buf[BTRFS_SEND_BUF_SIZE]
+		__attribute__((aligned(sizeof(unsigned long))));
 
 	int cmd;
 	struct btrfs_cmd_header *cmd_hdr;
@@ -41,7 +42,7 @@ struct btrfs_send_stream {
 
 	struct btrfs_send_ops *ops;
 	void *user;
-};
+} __attribute__((aligned(sizeof(unsigned long))));
 
 /*
  * Read len bytes to buf.
-- 
2.29.2