Re: [PATCH 1/2] fs: fork do_splice_copy_file_range() from do_splice_direct()

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Nov 29, 2023 at 10:07 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> The new helper is meant to be called from context of ->copy_file_range()
> methods instead of do_splice_direct().
>
> Currently, the only difference is that do_splice_copy_file_range() does
> not take a splice flags argument and it asserts that file_start_write()
> was called.
>
> Soon, do_splice_direct() will be called without file_start_write() held.
>
> Use the new helper from __ceph_copy_file_range(), that was incorrectly
> passing the copy_file_range() flags argument as splice flags argument
> to do_splice_direct(). the value of flags was 0, so no actual bug fix.
>
> Move the definition of both helpers to linux/splice.h.
>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/ceph/file.c         |  9 ++---
>  fs/read_write.c        |  6 ++--
>  fs/splice.c            | 82 ++++++++++++++++++++++++++++++------------
>  include/linux/fs.h     |  2 --
>  include/linux/splice.h | 13 ++++---
>  5 files changed, 75 insertions(+), 37 deletions(-)
>
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 3b5aae29e944..7c2db78e2c6e 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 = do_splice_copy_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 = do_splice_copy_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..555514cdad53 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 do_splice_copy_file_range(file_in, &pos_in, file_out, &pos_out,
> +                               len > MAX_RW_COUNT ? MAX_RW_COUNT : len);
>  }
>  EXPORT_SYMBOL(generic_copy_file_range);
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 3fce5f6072dd..3bb4936f8b70 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1158,8 +1158,15 @@ static int direct_splice_actor(struct pipe_inode_info *pipe,
>  {
>         struct file *file = sd->u.file;
>
> -       return do_splice_from(pipe, file, sd->opos, sd->total_len,
> -                             sd->flags);
> +       return do_splice_from(pipe, file, sd->opos, sd->total_len, sd->flags);
> +}
> +
> +static int copy_file_range_splice_actor(struct pipe_inode_info *pipe,
> +                                       struct splice_desc *sd)
> +{
> +       struct file *file = sd->u.file;
> +
> +       return do_splice_from(pipe, file, sd->opos, sd->total_len, sd->flags);
>  }
>
>  static void direct_file_splice_eof(struct splice_desc *sd)
> @@ -1170,25 +1177,10 @@ 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 +1199,60 @@ 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);
>
> +/**
> + * do_splice_copy_file_range - splices data 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 do_splice_copy_file_range(struct file *in, loff_t *ppos, struct file *out,
> +                              loff_t *opos, size_t len)

FYI, I renamed do_splice_vfs_copy_file_range => splice_file_range in v2
for brevity.

Thanks,
Amir.