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

[Wang Yugui <wangyugui@e16-tech.com>]

Hi, Sheng

> 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;

Can we move 'int cmd' to before 'char read_buf' too?

There is a hole between 'int fd' and 'char read_buf' after the
addiatioin of '__attribute__((aligned(sizeof(unsigned long))))'
in x86_64.

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/01/03

>  	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