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 24D7BC432C1 for ; Tue, 24 Sep 2019 17:15:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED8F421841 for ; Tue, 24 Sep 2019 17:15:17 +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="x26N3942" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437174AbfIXRPR (ORCPT ); Tue, 24 Sep 2019 13:15:17 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:40231 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437098AbfIXRPQ (ORCPT ); Tue, 24 Sep 2019 13:15:16 -0400 Received: by mail-pl1-f196.google.com with SMTP id d22so1262802pll.7 for ; Tue, 24 Sep 2019 10:15:16 -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:in-reply-to:user-agent; bh=jOVfFic0aC/sB5K6AnmSRgDO07i2M/QIEQDEL1PuVhk=; b=x26N3942+DmdIQ1sRCqJ5F/bC1YLtOK5gp0j4tDmpD+uDTrXssvHxQG2YVcjD6HfhK yGEn0BAnN0cthtBy8XQxssnVwU0+80GxpDUVBft0NWqtm/3SvG9yQ/0R8otMOW1ebbPo KgbvajiW6NpTG/Ke9C6fDCw4dx7XBFd551aG9Nr+cFx75/J6LD9udfgGgAhG93OIQRBT Wvs1Y+gFMgIc+36WAO8VIxAGGxBd5RhKysLpKsKjKIxSw85jDw12ySAAfi6q7Z2Oe7Ss AdnWoT0zf6xW24PSiVracGyY6tJD2skJVr/01ls8Osjo2M2B7NpL6R2OIJdlvueiBe1J duvA== 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:in-reply-to:user-agent; bh=jOVfFic0aC/sB5K6AnmSRgDO07i2M/QIEQDEL1PuVhk=; b=nZc9/Xpeeexzu9fIE4mroXpy/svM56Tz56wQZ+R2bL4TBUXZVPlCk0H9vKt1ma37C5 vm34ixA+d8hkddXMQNXpVuNoPUQ3StW73nLDel2DLWds9+KU7obocY0i/8EzYWEmnKZi +3a8pddw23zxAUovJ/dfTZ3/tb5SWRP2sWhyYG/CnMXaRlSoGA6fSLYsczBkD83DZmNs i4UEuEYSwwHNIAZQm1lwBV53JGc/Dv/8xrpQEWe08KlQb5r58uGcK4Lz0BJuFrUWmRUr j7D3S6XqgjSrceZSjpNpwzGjWvThfszxDbpEieeh6pENjcTo0780EdAAPNV+LEtuDfoq ZJEQ== X-Gm-Message-State: APjAAAXkEEvMC1dQP/tGNJDejOrKgpnvDRScDvwe22zRzffiK53NHMkN 6ilB97/9i4/Iz6J3EsigL/s9Cw== X-Google-Smtp-Source: APXvYqzhc8tgADrAilSYxLfDN1ihN4fhwbQt1mfpzzPgaSyk/mADAci8CMyfKd00aTDwYc7EgZq7tg== X-Received: by 2002:a17:902:7002:: with SMTP id y2mr4112884plk.303.1569345315655; Tue, 24 Sep 2019 10:15:15 -0700 (PDT) Received: from vader ([2620:10d:c090:200::3:f972]) by smtp.gmail.com with ESMTPSA id l7sm491697pjy.12.2019.09.24.10.15.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Sep 2019 10:15:15 -0700 (PDT) Date: Tue, 24 Sep 2019 10:15:13 -0700 From: Omar Sandoval To: Jann Horn Cc: Jens Axboe , linux-fsdevel , linux-btrfs@vger.kernel.org, Dave Chinner , Linux API , Kernel Team , Andy Lutomirski Subject: Re: [RFC PATCH 2/3] fs: add RWF_ENCODED for writing compressed data Message-ID: <20190924171513.GA39872@vader> References: <230a76e65372a8fb3ec62ce167d9322e5e342810.1568875700.git.osandov@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Sep 19, 2019 at 05:44:12PM +0200, Jann Horn wrote: > On Thu, Sep 19, 2019 at 8:54 AM Omar Sandoval wrote: > > Btrfs can transparently compress data written by the user. However, we'd > > like to add an interface to write pre-compressed data directly to the > > filesystem. This adds support for so-called "encoded writes" via > > pwritev2(). > > > > A new RWF_ENCODED flags indicates that a write is "encoded". If this > > flag is set, iov[0].iov_base points to a struct encoded_iov which > > contains metadata about the write: namely, the compression algorithm and > > the unencoded (i.e., decompressed) length of the extent. iov[0].iov_len > > must be set to sizeof(struct encoded_iov), which can be used to extend > > the interface in the future. The remaining iovecs contain the encoded > > extent. > > > > A similar interface for reading encoded data can be added to preadv2() > > in the future. > > > > Filesystems must indicate that they support encoded writes by setting > > FMODE_ENCODED_IO in ->file_open(). > [...] > > +int import_encoded_write(struct kiocb *iocb, struct encoded_iov *encoded, > > + struct iov_iter *from) > > +{ > > + if (iov_iter_single_seg_count(from) != sizeof(*encoded)) > > + return -EINVAL; > > + if (copy_from_iter(encoded, sizeof(*encoded), from) != sizeof(*encoded)) > > + return -EFAULT; > > + if (encoded->compression == ENCODED_IOV_COMPRESSION_NONE && > > + encoded->encryption == ENCODED_IOV_ENCRYPTION_NONE) { > > + iocb->ki_flags &= ~IOCB_ENCODED; > > + return 0; > > + } > > + if (encoded->compression > ENCODED_IOV_COMPRESSION_TYPES || > > + encoded->encryption > ENCODED_IOV_ENCRYPTION_TYPES) > > + return -EINVAL; > > + if (!capable(CAP_SYS_ADMIN)) > > + return -EPERM; > > How does this capable() check interact with io_uring? Without having > looked at this in detail, I suspect that when an encoded write is > requested through io_uring, the capable() check might be executed on > something like a workqueue worker thread, which is probably running > with a full capability set. I discussed this more with Jens. You're right, per-IO permission checks aren't going to work. In fully-polled mode, we never get an opportunity to check capabilities in right context. So, this will probably require a new open flag.