Re: [PATCH] lib/core/coio_file: Use eio_sendfile_sync instead of a chunk mode

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Wed, Apr 10, 2019 at 10:36:24PM +0300, Cyrill Gorcunov wrote:
> eio library provides a portable version of sendfile syscall
> which works a way more efficient than explicit copying file
> by 4K chunks.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
> ---
> 
> Test app/fio.test.lua which uses this helper passed.
> 
>  src/lib/core/coio_file.c | 22 +++++++---------------
>  1 file changed, 7 insertions(+), 15 deletions(-)
> 
> diff --git a/src/lib/core/coio_file.c b/src/lib/core/coio_file.c
> index c5b2db781..27806d7d5 100644
> --- a/src/lib/core/coio_file.c
> +++ b/src/lib/core/coio_file.c
> @@ -588,22 +588,14 @@ coio_do_copyfile(eio_req *req)
>  		goto error_dest;
>  	}
>  
> -	enum { COPY_FILE_BUF_SIZE = 4096 };
> -
> -	char buf[COPY_FILE_BUF_SIZE];
> -
> -	while (true) {
> -		ssize_t nread = fio_read(source_fd, buf, sizeof(buf));
> -		if (nread < 0)
> -			goto error_copy;
> -
> -		if (nread == 0)
> -			break; /* eof */
> -
> -		ssize_t nwritten = fio_writen(dest_fd, buf, nread);
> -		if (nwritten < 0)
> -			goto error_copy;
> +	ssize_t nwritten = eio_sendfile_sync(dest_fd, source_fd, 0, st.st_size);
> +	if (nwritten != st.st_size) {
> +		say_syserror("sendfile, [%s -> %s]",
> +			     fio_filename(source_fd),
> +			     fio_filename(dest_fd));

Other coio/fio methods don't log errors so I don't think this one
should, either.

An extract from the sendfile manual page:

} sendfile() will transfer at most 0x7ffff000 (2,147,479,552) bytes,
} returning the number of bytes actually transferred. (This is true on
} both 32-bit and 64-bit systems.)

So I don't think using sendfile is equivalent to read+write...

> +		goto error_copy;
>  	}
> +
>  	req->result = 0;
>  	close(source_fd);
>  	close(dest_fd);