On Tue, Aug 27, 2019 at 11:06:23AM -0700, Omar Sandoval wrote: > On Tue, Aug 27, 2019 at 07:57:41AM -0400, Josef Bacik wrote: > > On Tue, Aug 27, 2019 at 09:26:21AM +0300, Nikolay Borisov wrote: > > > > > > > > > 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? > > > > > > > Subvolume encryption will be coming soon, but I'm less worried about the > > mechanics of how that will be used and more worried about making this > > interface > > work for that eventual future. I assume we'll want to be able to just blind > > copy the encrypted data instead of decrypting into the send stream and then > > re-encrypting on the other side. Which means we'll have two uses for this > > interface, and I want to make sure we're happy with it before it gets > > merged. > > Thanks, > > > > Josef > > Right, I think the only way to do this would be to blindly send > encrypted data, and leave the key management to a higher layer. > > Looking at the ioctl definition: > > struct btrfs_ioctl_compressed_pwrite_args { > __u64 offset; /* in */ > __u32 orig_len; /* in */ > __u32 compressed_len; /* in */ > __u32 compress_type; /* in */ > __u32 reserved[9]; > void __user *buf; /* in */ > } __attribute__ ((__packed__)); > > I think there are enough reserved fields in there for, e.g., encryption > type, any key management-related things we might need to stuff in, etc. > But the naming would be pretty bad if we extended it this way. Maybe > compressed write -> raw write, orig_len -> num_bytes, compressed_len -> > disk_num_bytes? > > struct btrfs_ioctl_raw_pwrite_args { > __u64 offset; /* in */ > __u32 num_bytes; /* in */ > __u32 disk_num_bytes; /* in */ > __u32 compress_type; /* in */ > __u32 reserved[9]; > void __user *buf; /* in */ > } __attribute__ ((__packed__)); > > Besides the naming, I don't think anything else would need to change for > now. And if we decide that we don't want encrypted send/receive, then > fine, this naming is still okay.
Oh, and at this again, compression and encryption are only u8 in the extent item, and we have an extra u16 for "other_encoding", so it'd probably be safe to make it: struct btrfs_ioctl_raw_pwrite_args { __u64 offset; /* in */ __u32 num_bytes; /* in */ __u32 disk_num_bytes; /* in */ __u8 compression; /* in */ __u8 encryption; /* in */ __u16 other_encoding; /* in */ __u32 reserved[9]; void __user *buf; /* in */ } __attribute__ ((__packed__));