From patchwork Tue Sep 14 14:17:48 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jens Axboe X-Patchwork-Id: 12493609 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=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 8BC62C4332F for ; Tue, 14 Sep 2021 14:18:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F4CD6108B for ; Tue, 14 Sep 2021 14:18:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233526AbhINOTj (ORCPT ); Tue, 14 Sep 2021 10:19:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233534AbhINOTN (ORCPT ); Tue, 14 Sep 2021 10:19:13 -0400 Received: from mail-io1-xd42.google.com (mail-io1-xd42.google.com [IPv6:2607:f8b0:4864:20::d42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9DD1FC061764 for ; Tue, 14 Sep 2021 07:17:56 -0700 (PDT) Received: by mail-io1-xd42.google.com with SMTP id g9so17249546ioq.11 for ; Tue, 14 Sep 2021 07:17:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=z7c8syQSjn5yBCKSSFtxNAKMp+iDYztMNgRmqIUn/y4=; b=ot4kB+Ih3QhytiaAfiLfEBF0Igh+Z2lvHWRkckVTvNJwEqmcJ/J1Vu9OAEa44SAd+J 7+HPo2kLRSDdZFK97efrKeLZ9ucPXeCut16oOePaS5gtMCeBNmi+LZIVpBy8srXdin2u 1p1vemZiAsGj4p9qBMCwYUYecc5m1fbXhBd9JmL8SGyyGaI0kOjFTEWxIjKyjb588yn/ j9bQW78HkWFbcvcTAOSt8gSwoqb5G/bJng3dqqYDCvfaR6nq1sOTtlfXH0MWfjm+U6xf S9BBNadbk/bELyDBwb6R287yv+jEm7xkk3R1V7duDv+yzi9t2/Evv4DBhvZTQh/aLRsr Gbuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=z7c8syQSjn5yBCKSSFtxNAKMp+iDYztMNgRmqIUn/y4=; b=3XI4/b7BKJTK+wm1bEVxLChS/2pAVJkL5zweaWDN+2hDa0l/BEGxEObCUIRG2vqy3d 4CzQEAb2QIY+VynDJsvWyvJ8ruxEhPs2WfaaxApNEgFieX7geh4Q47XBFyNQ54xWWfIM 7PATATEBeVpp2kTHUIoQI9a9N6RZqQtpi1qwkHzebPV/TYPqKxevhpnwOoRuGVFbfgvf v1Kt2YS1OB2ntkPkCa8k+aNdk0gJ7u+kvNJN7WaKj3o3ezL3ocoJHeBHOAUSc1yNW0Mx OaxppCQJDeTIZvaT9jMDH5fk0zz+wZVHp8hdODGsC5st6BC9/mThosUJksMoNl2oP52r GJdw== X-Gm-Message-State: AOAM531RjV6PULe/UZz9N4MaJvy6MANI2UJOtpL+RoJOMiLeDEGKEOC/ lgk8UuAdazioJGJNBGRT2EozGA== X-Google-Smtp-Source: ABdhPJwHJDdCWKE4tIBEqkfAhQtAcMRw/R/WoKebKZMWNAPpX4dOsCBr92Sms5Kzb0IRQ9Y2wbj9RA== X-Received: by 2002:a6b:5c17:: with SMTP id z23mr13746798ioh.3.1631629075962; Tue, 14 Sep 2021 07:17:55 -0700 (PDT) Received: from p1.localdomain ([207.135.234.126]) by smtp.gmail.com with ESMTPSA id p135sm6673803iod.26.2021.09.14.07.17.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Sep 2021 07:17:55 -0700 (PDT) From: Jens Axboe To: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, Jens Axboe Subject: [PATCH 1/3] iov_iter: add helper to save iov_iter state Date: Tue, 14 Sep 2021 08:17:48 -0600 Message-Id: <20210914141750.261568-2-axboe@kernel.dk> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210914141750.261568-1-axboe@kernel.dk> References: <20210914141750.261568-1-axboe@kernel.dk> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org In an ideal world, when someone is passed an iov_iter and returns X bytes, then X bytes would have been consumed/advanced from the iov_iter. But we have use cases that always consume the entire iterator, a few examples of that are iomap and bdev O_DIRECT. This means we cannot rely on the state of the iov_iter once we've called ->read_iter() or ->write_iter(). This would be easier if we didn't always have to deal with truncate of the iov_iter, as rewinding would be trivial without that. We recently added a commit to track the truncate state, but that grew the iov_iter by 8 bytes and wasn't the best solution. Implement a helper to save enough of the iov_iter state to sanely restore it after we've called the read/write iterator helpers. This currently only works for IOVEC/BVEC/KVEC as that's all we need, support for other iterator types are left as an exercise for the reader. Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wiacKV4Gh-MYjteU0LwNBSGpWrK-Ov25HdqB1ewinrFPg@mail.gmail.com/ Signed-off-by: Jens Axboe --- include/linux/uio.h | 15 +++++++++++++++ lib/iov_iter.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/include/linux/uio.h b/include/linux/uio.h index 5265024e8b90..984c4ab74859 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -27,6 +27,12 @@ enum iter_type { ITER_DISCARD, }; +struct iov_iter_state { + size_t iov_offset; + size_t count; + unsigned long nr_segs; +}; + struct iov_iter { u8 iter_type; bool data_source; @@ -55,6 +61,14 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i) return i->iter_type; } +static inline void iov_iter_save_state(struct iov_iter *iter, + struct iov_iter_state *state) +{ + state->iov_offset = iter->iov_offset; + state->count = iter->count; + state->nr_segs = iter->nr_segs; +} + static inline bool iter_is_iovec(const struct iov_iter *i) { return iov_iter_type(i) == ITER_IOVEC; @@ -233,6 +247,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages, ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages, size_t maxsize, size_t *start); int iov_iter_npages(const struct iov_iter *i, int maxpages); +void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state); const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags); diff --git a/lib/iov_iter.c b/lib/iov_iter.c index f2d50d69a6c3..755c10c5138c 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1972,3 +1972,39 @@ int import_single_range(int rw, void __user *buf, size_t len, return 0; } EXPORT_SYMBOL(import_single_range); + +/** + * iov_iter_restore() - Restore a &struct iov_iter to the same state as when + * iov_iter_save_state() was called. + * + * @i: &struct iov_iter to restore + * @state: state to restore from + * + * Used after iov_iter_save_state() to bring restore @i, if operations may + * have advanced it. + * + * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC + */ +void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state) +{ + if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) && + !iov_iter_is_kvec(i)) + return; + i->iov_offset = state->iov_offset; + i->count = state->count; + /* + * For the *vec iters, nr_segs + iov is constant - if we increment + * the vec, then we also decrement the nr_segs count. Hence we don't + * need to track both of these, just one is enough and we can deduct + * the other from that. ITER_KVEC and ITER_IOVEC are the same struct + * size, so we can just increment the iov pointer as they are unionzed. + * ITER_BVEC _may_ be the same size on some archs, but on others it is + * not. Be safe and handle it separately. + */ + BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec)); + if (iov_iter_is_bvec(i)) + i->bvec -= state->nr_segs - i->nr_segs; + else + i->iov -= state->nr_segs - i->nr_segs; + i->nr_segs = state->nr_segs; +}