On 27.08.19 г. 0:36 ч., Josef Bacik wrote:
> On Thu, Aug 15, 2019 at 02:04:06PM -0700, Omar Sandoval wrote:
>> From: Omar Sandoval <osan...@fb.com>
>>
>> This adds an API for writing compressed data directly to the filesystem.
>> The use case that I have in mind is send/receive: currently, when
>> sending data from one compressed filesystem to another, the sending side
>> decompresses the data and the receiving side recompresses it before
>> writing it out. This is wasteful and can be avoided if we can just send
>> and write compressed extents. The send part will be implemented in a
>> separate series, as this ioctl can stand alone.
>>
>> The interface is essentially pwrite(2) with some extra information:
>>
>> - The input buffer contains the compressed data.
>> - Both the compressed and decompressed sizes of the data are given.
>> - The compression type (zlib, lzo, or zstd) is given.
>>
>> A more detailed description of the interface, including restrictions and
>> edge cases, is included in include/uapi/linux/btrfs.h.
>>
>> The implementation is similar to direct I/O: we have to flush any
>> ordered extents, invalidate the page cache, and do the io
>> tree/delalloc/extent map/ordered extent dance. From there, we can reuse
>> the compression code with a minor modification to distinguish the new
>> ioctl from writeback.
>>
>
> I've looked at this a few times, the locking and space reservation stuff look
> right. What about encrypted send/recieve? Are we going to want to use this
> to
> just blind copy encrypted data without having to decrypt/re-encrypt? Should
> this be taken into consideration for this interface? I'll think more about
> it,
> but I can't really see any better option than this. Thanks,
The main problem is we don't have encryption implemented. And one of the
larger aspects of the encryption support is going to be how we are
storing the encryption keys. E.g. should they be part of the send
format? Or are we going to limit send/receive based on whether the
source/dest have transferred encryption keys out of line?
>
> Josef
>
