Re: [PATCH 3/4] copy_file_range: splice with holes

[Amir Goldstein <amir73il@gmail.com>]

On Thu, May 10, 2018 at 4:58 AM, Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
>
> copy_file_range calls do_splice_direct() if fs->clone_file_range
> or fs->copy_file_range() is not available. However, do_splice_direct()
> converts holes to zeros. Detect holes in the file_in range, and
> create them in the corresponding file_out range.
>
> If there is already data present at the offset in file_out, attempt
> to punch a hole there. If the operation is not supported, fall
> back to performing splice on the whole range.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/read_write.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 58 insertions(+), 4 deletions(-)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 1b8fc9eada69..e765fec656af 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -20,6 +20,7 @@
>  #include <linux/compat.h>
>  #include <linux/mount.h>
>  #include <linux/fs.h>
> +#include <linux/falloc.h>
>  #include "internal.h"
>
>  #include <linux/uaccess.h>
> @@ -1547,7 +1548,8 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
>  {
>         struct inode *inode_in = file_inode(file_in);
>         struct inode *inode_out = file_inode(file_out);
> -       ssize_t ret = 0;
> +       ssize_t ret = 0, total = 0;
> +       loff_t size, end;
>
>         if (len == 0)
>                 return 0;
> @@ -1572,10 +1574,62 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
>                 if (ret != -EOPNOTSUPP)
>                         return ret;
>         }
> +
>  splice:
> -       ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
> -                       len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
> -       return ret;
> +       while (total < len) {
> +               end = vfs_llseek(file_in, pos_in, SEEK_HOLE);
> +
> +               /* Starting position is already in a hole */
> +               if (end == pos_in)
> +                       goto hole;
> +               size = end - pos_in;
> +do_splice:
> +               if (size > len - total)
> +                       size = len - total;
> +               ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
> +                               size, 0);

I wonder, can do_splice_direct() return short copy (< size)?
If so, code below will try to punch a zero length hole.
Best put some protection here, don't you think?

> +               if (ret < 0)
> +                       goto out;
> +               total += ret;
> +               if (total == len)
> +                       break;
> +hole:
> +               end = vfs_llseek(file_in, pos_in, SEEK_DATA);
> +               if (end < 0) {
> +                       ret = end;
> +                       goto out;
> +               }
> +               size = end - pos_in;
> +               if (size > len - total)
> +                       size = len - total;
> +               /* Data on offset, punch holes */
> +               if (i_size_read(file_out->f_inode) > pos_out) {
> +                       ret = vfs_fallocate(file_out,
> +                                       FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> +                                       pos_out, size);

I'm afraid you have more re-factoring to do vfs_fallocate() does
file_start_write() -
you probably need do_fallocate().


> +                       if (ret < 0) {
> +                               /*
> +                                * The filesystem does not support punching
> +                                * holes. Perform splice on the remaining range.
> +                                */
> +                               if (ret == -EOPNOTSUPP) {
> +                                       size = len - total;
> +                                       goto do_splice;
> +                               }
> +                               goto out;
> +                       }
> +               }
> +               if (ret < 0) {
> +                       ret = end;
> +                       goto out;
> +               }
> +               pos_out += size;
> +               pos_in = end;
> +               total += size;
> +       }
> +
> +out:
> +       return total ? total : ret;
>  }
>
>  /*
> --
> 2.16.3
>
> --
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