Re: [PATCH 3/3] ovl: Use splice_with_holes in copy_up

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On 05/03/2018 02:57 PM, Amir Goldstein wrote:
> On Thu, May 3, 2018 at 6:26 PM, Goldwyn Rodrigues <rgoldwyn@xxxxxxx> wrote:
>> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>>
>> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>> ---
>>  fs/overlayfs/copy_up.c |  2 +-
>>  fs/read_write.c        | 10 ++++++----
>>  include/linux/fs.h     |  2 ++
>>  3 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
>> index 8bede0742619..6634a85255ae 100644
>> --- a/fs/overlayfs/copy_up.c
>> +++ b/fs/overlayfs/copy_up.c
>> @@ -175,7 +175,7 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
>>                         break;
>>                 }
>>
>> -               bytes = do_splice_direct(old_file, &old_pos,
>> +               bytes = splice_with_holes(old_file, &old_pos,
>>                                          new_file, &new_pos,
>>                                          this_len, SPLICE_F_MOVE);
> 
> 
> Add.. you can remove this comment above :)
>         /* FIXME: copy up sparse files efficiently */
> 
> For the record, when I added vfs_clone_file_range() above,
> Dave Chinner has suggested to replace the entire block with
> vfs_copy_file_range(), which would do all the fallbacks.
> Since then, vfs_copy_file_range() gained "try to clone first".
> 
> There are still differences between the loop in this function and
> the loop in vfs_copy_file_range(). Perhaps the differences could
> be smoothed away, I did not check recently.

There is a difference. copy_file_range(2) or do_splice_direct() can
return short writes. I think this loop is performed to cover short writes.

I suppose we could remove the clone_file_range() before the loop and
replace the do_splice_direct() with vfs_copy_file_range().

-- 
Goldwyn



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