Re: Feature Request for cp(1) utility, consider Btrfs ioctl clone range support

[Jeff liu]

Hi Pádraig,

Thanks for your comments!

> On 08/10/2011 10:31 AM, Jeff Liu wrote:
>> Hello,
>> 
>> I just found a cool feature in Btrfs for cloning partially source file
>> to the destination by specifying the desired offset and length to be copied.
>> 
>> The call interface is something like below:
>> struct btrfs_clone_range_args cr;
>> cr.src_fd = source_desc;
>> cr.src_offset = (uint64_t) offset;
>> cr.src_length = (uint64_t) length;
>> cr.dest_offset = (uint64_t) d_offset;
>> ioctl(dest_fd, BTRFS_IOC_CLONE_RANGE, &args);
>> 
>> cp(1) has already works with "reflink" supported for a long time, IMHO,
>> this new feature could improve it to some extent.
>> Is it acceptable to add a new option like
>> "--reflink-range=src_offset,src_length,dst_offset" to clone partially
>> source file?
>> In this way, if reflink-range is triggered, cp(1) will try to parse the
>> offset and length which are separated by comma,
>> then try to clone src_length bytes from src_offset to the destination
>> file started at dst_offset.
>> if reflink-range failed, just let cp(1) fail with appropriate error info.
>> 
>> I'd like to implement it if you guys think it does make sense. :-P.
> 
> IMHO I don't think this level of control is needed in `cp`.

If you think it became useful to other coreutils stuff in the future, please 
let me know, I would like to work on it.

Regards,
-Jeff
> 
> cheers,
> Pádraig.