Re: [1/4] vmsplice: lift import_iovec() into do_vmsplice()

[Andrei Vagin <avagin@virtuozzo.com>]

On Mon, May 28, 2018 at 11:20:10PM +0100, Al Viro wrote:
> From: Al Viro <viro@zeniv.linux.org.uk>
> 
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
>  fs/splice.c | 69 ++++++++++++++++++++++++++-----------------------------------
>  1 file changed, 29 insertions(+), 40 deletions(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 005d09cf3fa8..920ff0b20e53 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1242,38 +1242,26 @@ static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
>   * For lack of a better implementation, implement vmsplice() to userspace
>   * as a simple copy of the pipes pages to the user iov.
>   */
> -static long vmsplice_to_user(struct file *file, const struct iovec __user *uiov,
> -			     unsigned long nr_segs, unsigned int flags)
> +static long vmsplice_to_user(struct file *file, struct iov_iter *iter,
> +			     unsigned int flags)
>  {
> -	struct pipe_inode_info *pipe;
> -	struct splice_desc sd;
> -	long ret;
> -	struct iovec iovstack[UIO_FASTIOV];
> -	struct iovec *iov = iovstack;
> -	struct iov_iter iter;
> +	struct pipe_inode_info *pipe = get_pipe_info(file);
> +	struct splice_desc sd = {
> +		.total_len = iov_iter_count(iter),
> +		.flags = flags,
> +		.u.data = iter
> +	};
> +	long ret = 0;
>  
> -	pipe = get_pipe_info(file);
>  	if (!pipe)
>  		return -EBADF;
>  
> -	ret = import_iovec(READ, uiov, nr_segs,
> -			   ARRAY_SIZE(iovstack), &iov, &iter);
> -	if (ret < 0)
> -		return ret;
> -
> -	sd.total_len = iov_iter_count(&iter);
> -	sd.len = 0;
> -	sd.flags = flags;
> -	sd.u.data = &iter;
> -	sd.pos = 0;
> -
>  	if (sd.total_len) {
>  		pipe_lock(pipe);
>  		ret = __splice_from_pipe(pipe, &sd, pipe_to_user);
>  		pipe_unlock(pipe);
>  	}
>  
> -	kfree(iov);
>  	return ret;
>  }
>  
> @@ -1282,14 +1270,11 @@ static long vmsplice_to_user(struct file *file, const struct iovec __user *uiov,
>   * as splice-from-memory, where the regular splice is splice-from-file (or
>   * to file). In both cases the output is a pipe, naturally.
>   */
> -static long vmsplice_to_pipe(struct file *file, const struct iovec __user *uiov,
> -			     unsigned long nr_segs, unsigned int flags)
> +static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
> +			     unsigned int flags)
>  {
>  	struct pipe_inode_info *pipe;
> -	struct iovec iovstack[UIO_FASTIOV];
> -	struct iovec *iov = iovstack;
> -	struct iov_iter from;
> -	long ret;
> +	long ret = 0;
>  	unsigned buf_flag = 0;
>  
>  	if (flags & SPLICE_F_GIFT)
> @@ -1299,19 +1284,13 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *uiov,
>  	if (!pipe)
>  		return -EBADF;
>  
> -	ret = import_iovec(WRITE, uiov, nr_segs,
> -			   ARRAY_SIZE(iovstack), &iov, &from);
> -	if (ret < 0)
> -		return ret;
> -
>  	pipe_lock(pipe);
>  	ret = wait_for_space(pipe, flags);
>  	if (!ret)
> -		ret = iter_to_pipe(&from, pipe, buf_flag);
> +		ret = iter_to_pipe(iter, pipe, buf_flag);
>  	pipe_unlock(pipe);
>  	if (ret > 0)
>  		wakeup_pipe_readers(pipe);
> -	kfree(iov);
>  	return ret;
>  }
>  
> @@ -1331,29 +1310,39 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *uiov,
>   * Currently we punt and implement it as a normal copy, see pipe_to_user().
>   *
>   */
> -static long do_vmsplice(int fd, const struct iovec __user *iov,
> +static long do_vmsplice(int fd, const struct iovec __user *uiov,
>  			unsigned long nr_segs, unsigned int flags)
>  {
> +	struct iovec iovstack[UIO_FASTIOV];
> +	struct iovec *iov = iovstack;
> +	struct iov_iter iter;
>  	struct fd f;
>  	long error;
>  
>  	if (unlikely(flags & ~SPLICE_F_ALL))
>  		return -EINVAL;
> -	if (unlikely(nr_segs > UIO_MAXIOV))
> -		return -EINVAL;
> -	else if (unlikely(!nr_segs))
> +
> +	error = import_iovec(READ, uiov, nr_segs,
> +			   ARRAY_SIZE(iovstack), &iov, &iter);

import_iovec should be called with WRITE, if we are going to call
vmsplice_to_pipe().

> +	if (error < 0)
> +		return error;
> +
> +	if (!iov_iter_count(&iter)) {
> +		kfree(iov);
>  		return 0;
> +	}
>  
>  	error = -EBADF;
>  	f = fdget(fd);
>  	if (f.file) {
>  		if (f.file->f_mode & FMODE_WRITE)
> -			error = vmsplice_to_pipe(f.file, iov, nr_segs, flags);
> +			error = vmsplice_to_pipe(f.file, &iter, flags);
>  		else if (f.file->f_mode & FMODE_READ)
> -			error = vmsplice_to_user(f.file, iov, nr_segs, flags);
> +			error = vmsplice_to_user(f.file, &iter, flags);
>  
>  		fdput(f);
>  	}
> +	kfree(iov);
>  
>  	return error;
>  }