linux-kernel - Re: [PATCH RESEND] splice: introduce FMODE_SPLICE_READ and FMODE_SPLICE

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Date:   Wed, 11 Jan 2017 07:20:13 -0500
From:   Jeff Layton <jlayton@...hat.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     "J . Bruce Fields" <bfields@...ldses.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mbenes@...e.cz, jack@...e.cz
Subject: Re: [PATCH RESEND] splice: introduce FMODE_SPLICE_READ and
 FMODE_SPLICE_WRITE

On Wed, 2017-01-11 at 10:51 +0100, Johannes Thumshirn wrote:
> Introduce FMODE_SPLICE_READ and FMODE_SPLICE_WRITE. These modes check
> whether it is legal to read or write a file using splice. Both get
> automatically set on regular files and are not checked when a 'struct
> fileoperations' includes the splice_{read,write} methods.
> 

Could you add a description of the problem that this solves? I assume
you hit a problem trying to splice to/from a non-regular file, but it'd
be good to know what that problem was.

Thanks,

> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> ---
>  fs/open.c          | 4 ++++
>  fs/splice.c        | 6 ++++++
>  include/linux/fs.h | 5 +++++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 9921f70..b71259c 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -733,6 +733,10 @@ static int do_dentry_open(struct file *f,
>  	if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
>  		f->f_mode |= FMODE_ATOMIC_POS;
>  
> +	if (S_ISREG(inode->i_mode))
> +		f->f_mode |= FMODE_SPLICE_WRITE | FMODE_SPLICE_READ;
> +
> +
>  	f->f_op = fops_get(inode->i_fop);
>  	if (unlikely(WARN_ON(!f->f_op))) {
>  		error = -ENODEV;
> diff --git a/fs/splice.c b/fs/splice.c
> index 873d831..b0cfcb2 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -397,6 +397,9 @@ static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
>  	if (pipe->nrbufs == pipe->buffers)
>  		return -EAGAIN;
>  
> +	if (unlikely(!(in->f_mode & FMODE_SPLICE_READ)))
> +		return -EINVAL;
> +
>  	/*
>  	 * Try to keep page boundaries matching to source pagecache ones -
>  	 * it probably won't be much help, but...
> @@ -825,6 +828,9 @@ static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,
>  {
>  	ssize_t ret;
>  
> +	if (unlikely(!(out->f_mode & FMODE_SPLICE_WRITE)))
> +		return -EINVAL;
> +
>  	ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf);
>  	if (ret > 0)
>  		*ppos += ret;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 2ba0743..30477c5 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -143,6 +143,11 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>  /* File was opened by fanotify and shouldn't generate fanotify events */
>  #define FMODE_NONOTIFY		((__force fmode_t)0x4000000)
>  
> +/* File can be read using splice */
> +#define FMODE_SPLICE_READ       ((__force fmode_t)0x8000000)
> +/* File can be written using splice */
> +#define FMODE_SPLICE_WRITE      ((__force fmode_t)0x10000000)
> +
>  /*
>   * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
>   * that indicates that they should check the contents of the iovec are

-- 
Jeff Layton <jlayton@...hat.com>