Re: [PATCH v2 1/3] fs: fork splice_file_range() from do_splice_direct()

From: Jeff Layton <jlayton@kernel.org>
To: Amir Goldstein <amir73il@gmail.com>,
	Christian Brauner <brauner@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>,
	Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
	David Howells <dhowells@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	 Miklos Szeredi <miklos@szeredi.hu>,
	Al Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] fs: fork splice_file_range() from do_splice_direct()
Date: Thu, 30 Nov 2023 11:27:42 -0500	[thread overview]
Message-ID: <a0011d31ad58112a13a0cad5746095f508a3eb99.camel@kernel.org> (raw)
In-Reply-To: <20231130141624.3338942-2-amir73il@gmail.com>

On Thu, 2023-11-30 at 16:16 +0200, Amir Goldstein wrote:
> In preparation of calling do_splice_direct() without file_start_write()
> held, create a new helper splice_file_range(), to be called from context
> of ->copy_file_range() methods instead of do_splice_direct().
> 
> Currently, the only difference is that splice_file_range() does not take
> flags argument and that it asserts that file_start_write() is held, but
> we factor out a common helper do_splice_direct_actor() that will be used
> later.
> 
> Use the new helper from __ceph_copy_file_range(), that was incorrectly
> passing to do_splice_direct() the copy flags argument as splice flags.
> The value of copy flags in ceph is always 0, so it is a smenatic bug fix.
> 
> Move the declaration of both helpers to linux/splice.h.
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/ceph/file.c         |  9 +++---
>  fs/read_write.c        |  6 ++--
>  fs/splice.c            | 71 ++++++++++++++++++++++++++++++------------
>  include/linux/fs.h     |  2 --
>  include/linux/splice.h | 13 +++++---
>  5 files changed, 66 insertions(+), 35 deletions(-)
> 
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 3b5aae29e944..f11de6e1f1c1 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -12,6 +12,7 @@
>  #include <linux/falloc.h>
>  #include <linux/iversion.h>
>  #include <linux/ktime.h>
> +#include <linux/splice.h>
>  
>  #include "super.h"
>  #include "mds_client.h"
> @@ -3010,8 +3011,8 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
>  		 * {read,write}_iter, which will get caps again.
>  		 */
>  		put_rd_wr_caps(src_ci, src_got, dst_ci, dst_got);
> -		ret = do_splice_direct(src_file, &src_off, dst_file,
> -				       &dst_off, src_objlen, flags);
> +		ret = splice_file_range(src_file, &src_off, dst_file, &dst_off,
> +					src_objlen);
>  		/* Abort on short copies or on error */
>  		if (ret < (long)src_objlen) {
>  			doutc(cl, "Failed partial copy (%zd)\n", ret);
> @@ -3065,8 +3066,8 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
>  	 */
>  	if (len && (len < src_ci->i_layout.object_size)) {
>  		doutc(cl, "Final partial copy of %zu bytes\n", len);
> -		bytes = do_splice_direct(src_file, &src_off, dst_file,
> -					 &dst_off, len, flags);
> +		bytes = splice_file_range(src_file, &src_off, dst_file,
> +					  &dst_off, len);
>  		if (bytes > 0)
>  			ret += bytes;
>  		else
> diff --git a/fs/read_write.c b/fs/read_write.c
> index f791555fa246..642c7ce1ced1 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1423,10 +1423,8 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
>  				struct file *file_out, loff_t pos_out,
>  				size_t len, unsigned int flags)
>  {
> -	lockdep_assert(file_write_started(file_out));
> -
> -	return do_splice_direct(file_in, &pos_in, file_out, &pos_out,
> -				len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
> +	return splice_file_range(file_in, &pos_in, file_out, &pos_out,
> +				 min_t(size_t, len, MAX_RW_COUNT));
>  }
>  EXPORT_SYMBOL(generic_copy_file_range);
>  
> diff --git a/fs/splice.c b/fs/splice.c
> index 3fce5f6072dd..9007b2c8baa8 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1170,25 +1170,10 @@ static void direct_file_splice_eof(struct splice_desc *sd)
>  		file->f_op->splice_eof(file);
>  }
>  
> -/**
> - * do_splice_direct - splices data directly between two files
> - * @in:		file to splice from
> - * @ppos:	input file offset
> - * @out:	file to splice to
> - * @opos:	output file offset
> - * @len:	number of bytes to splice
> - * @flags:	splice modifier flags
> - *
> - * Description:
> - *    For use by do_sendfile(). splice can easily emulate sendfile, but
> - *    doing it in the application would incur an extra system call
> - *    (splice in + splice out, as compared to just sendfile()). So this helper
> - *    can splice directly through a process-private pipe.
> - *
> - * Callers already called rw_verify_area() on the entire range.
> - */
> -long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
> -		      loff_t *opos, size_t len, unsigned int flags)
> +static long do_splice_direct_actor(struct file *in, loff_t *ppos,
> +				   struct file *out, loff_t *opos,
> +				   size_t len, unsigned int flags,
> +				   splice_direct_actor *actor)
>  {
>  	struct splice_desc sd = {
>  		.len		= len,
> @@ -1207,14 +1192,60 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
>  	if (unlikely(out->f_flags & O_APPEND))
>  		return -EINVAL;
>  
> -	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
> +	ret = splice_direct_to_actor(in, &sd, actor);
>  	if (ret > 0)
>  		*ppos = sd.pos;
>  
>  	return ret;
>  }
> +/**
> + * do_splice_direct - splices data directly between two files
> + * @in:		file to splice from
> + * @ppos:	input file offset
> + * @out:	file to splice to
> + * @opos:	output file offset
> + * @len:	number of bytes to splice
> + * @flags:	splice modifier flags
> + *
> + * Description:
> + *    For use by do_sendfile(). splice can easily emulate sendfile, but
> + *    doing it in the application would incur an extra system call
> + *    (splice in + splice out, as compared to just sendfile()). So this helper
> + *    can splice directly through a process-private pipe.
> + *
> + * Callers already called rw_verify_area() on the entire range.
> + */
> +long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
> +		      loff_t *opos, size_t len, unsigned int flags)
> +{
> +	return do_splice_direct_actor(in, ppos, out, opos, len, flags,
> +				      direct_splice_actor);
> +}
>  EXPORT_SYMBOL(do_splice_direct);
>  
> +/**
> + * splice_file_range - splices data between two files for copy_file_range()
> + * @in:		file to splice from
> + * @ppos:	input file offset
> + * @out:	file to splice to
> + * @opos:	output file offset
> + * @len:	number of bytes to splice
> + *
> + * Description:
> + *    For use by generic_copy_file_range() and ->copy_file_range() methods.
> + *
> + * Callers already called rw_verify_area() on the entire range.
> + */
> +long splice_file_range(struct file *in, loff_t *ppos, struct file *out,
> +		       loff_t *opos, size_t len)
> +{
> +	lockdep_assert(file_write_started(out));
> +
> +	return do_splice_direct_actor(in, ppos, out, opos, len, 0,
> +				      direct_splice_actor);
> +}
> +EXPORT_SYMBOL(splice_file_range);
> +
>  static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
>  {
>  	for (;;) {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ae0e2fb7bcea..04422a0eccdd 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3052,8 +3052,6 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
>  			 size_t len, unsigned int flags);
>  extern ssize_t iter_file_splice_write(struct pipe_inode_info *,
>  		struct file *, loff_t *, size_t, unsigned int);
> -extern long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
> -		loff_t *opos, size_t len, unsigned int flags);
>  
>  
>  extern void
> diff --git a/include/linux/splice.h b/include/linux/splice.h
> index 6c461573434d..49532d5dda52 100644
> --- a/include/linux/splice.h
> +++ b/include/linux/splice.h
> @@ -80,11 +80,14 @@ extern ssize_t add_to_pipe(struct pipe_inode_info *,
>  long vfs_splice_read(struct file *in, loff_t *ppos,
>  		     struct pipe_inode_info *pipe, size_t len,
>  		     unsigned int flags);
> -extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
> -				      splice_direct_actor *);
> -extern long do_splice(struct file *in, loff_t *off_in,
> -		      struct file *out, loff_t *off_out,
> -		      size_t len, unsigned int flags);
> +ssize_t splice_direct_to_actor(struct file *file, struct splice_desc *sd,
> +			       splice_direct_actor *actor);
> +long do_splice(struct file *in, loff_t *off_in, struct file *out,
> +	       loff_t *off_out, size_t len, unsigned int flags);
> +long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
> +		      loff_t *opos, size_t len, unsigned int flags);
> +long splice_file_range(struct file *in, loff_t *ppos, struct file *out,
> +		       loff_t *opos, size_t len);
>  
>  extern long do_tee(struct file *in, struct file *out, size_t len,
>  		   unsigned int flags);

Looks OK to me:

Acked-by: Jeff Layton <jlayton@kernel.org>