From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C92ADC3A5A3 for ; Tue, 27 Aug 2019 18:22:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9328820674 for ; Tue, 27 Aug 2019 18:22:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=osandov-com.20150623.gappssmtp.com header.i=@osandov-com.20150623.gappssmtp.com header.b="LUH/WKne" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730047AbfH0SWo (ORCPT ); Tue, 27 Aug 2019 14:22:44 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:38020 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727064AbfH0SWo (ORCPT ); Tue, 27 Aug 2019 14:22:44 -0400 Received: by mail-pg1-f194.google.com with SMTP id e11so13132962pga.5 for ; Tue, 27 Aug 2019 11:22:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=osandov-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=mBL/o5XxXh1iLBl41F+c7xLXiKl8oRwCCLDrldkObXQ=; b=LUH/WKnew1kAALTdxWWLaAOksTe3PJ/1Gzk4Pc/6Ki8xbSkWoX6iT376k7vBjsM1hZ MNlL3iLfnUzgNnFFgYkRxLXx7nHCtPUK2LIGTj4iE6YUIp8V4imMeDJSyKbMIThUjepr vd236qDjAjZjyXHup+YbPoWnXhafSD5NRMBWT7dYWK1X5PXufOy1BHZVoDfE3gtlujb7 m81GfPwTyGVqbqGZ7IDv5i5EGtIfV/4h6MvzzR/8vjO/8oelTh/Qf5HnnDzDMiLyb6k3 juOiZIv8rzE0ilixbk58oEYKATbornNhuW2hIhRGZkP0VrrlGthxUNn/ibbglCdr3dFK PmbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=mBL/o5XxXh1iLBl41F+c7xLXiKl8oRwCCLDrldkObXQ=; b=OcCvXTMfU2xZ+tVmrn80jJfC9D9NPxS5LZ80w1Dfh/CvhuJg7d5CUHzAL6KZ7BimIw Md1abCtItLyqb05ZPkIB/jz7B5ggGWRLyEM7IsCUNnwWPnE5LqjePlVxmGUWFUokirsf 0vXAjSgdIO8V5DVCexUVj5qvaCt8kK1Q+17FyVE6eEfR0iRrEpATp2SJTUJJM29cH8dP +3AnTjD2VotgiDNwNAVasFRJEb2DfnpbnDx+IJA3RSDNTNwe1/qPttoQMUhv5Dn4RZ3m pQDZrB86U07Xh3mUsv7Q+ocshNUcxy9fiVhUHd8450qi2uChY+Ga+0sJ7V2GVaA4rNrQ uSOg== X-Gm-Message-State: APjAAAXOVaoa+6LeDSrPB0EaHWo6hNwOC4Zm3bP+bzt1sd0rb7x9UsVm /B2EajlJENBNKDi8zC4h9iysGg== X-Google-Smtp-Source: APXvYqwJno2qsaN4e75hLkEegLaSgHbZlrjEROvQc0rCCMng7GRun/6Ddh2Zq3AZ2IH3Uq35/S3PzQ== X-Received: by 2002:a17:90a:326e:: with SMTP id k101mr53771pjb.15.1566930163343; Tue, 27 Aug 2019 11:22:43 -0700 (PDT) Received: from vader ([2620:10d:c090:200::2:56d8]) by smtp.gmail.com with ESMTPSA id v22sm66013pgk.69.2019.08.27.11.22.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Aug 2019 11:22:42 -0700 (PDT) Date: Tue, 27 Aug 2019 11:22:42 -0700 From: Omar Sandoval To: Josef Bacik Cc: Nikolay Borisov , kernel-team@fb.com, linux-btrfs@vger.kernel.org Subject: Re: [RFC PATCH 5/5] Btrfs: add ioctl for directly writing compressed data Message-ID: <20190827182242.GA23051@vader> References: <78747c3028ce91db9856e7fbd98ccbb2609acdc6.1565900769.git.osandov@fb.com> <20190826213618.qdsivmmwwlxkqtxc@macbook-pro-91.dhcp.thefacebook.com> <20190827115740.n57xrl7i7pshjkey@macbook-pro-91.dhcp.thefacebook.com> <20190827180623.GB28029@vader> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190827180623.GB28029@vader> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org 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 > > > >> > > > >> 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__));