From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 91C913B584B for ; Wed, 4 Mar 2026 14:04:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772633079; cv=none; b=oMo7K/XcjSJXKzq6rAhMkFNRzMFi3LoSS6Ejes8+GGfPVTljt+yKJChefcmOPv/FngGFt4SlAkSRjVGQ8+nOwsc4Eq4sFNMZJK6inl4yToF5Fj0AQIkc/85RBhxPXo7qjJHqGpsQ4p67ifn0MKnkcnLZdpzsz8/g97UX3kV5xl0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772633079; c=relaxed/simple; bh=IP/juZtoL3vcS4yj+idXFsVpTc19MnDYbAUh31HpUdU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Qr70RGirwLFxT9/r9UQFrSnTtCuw6T7BqBhp0WL2DmPGGpBmbhNSh694HqVeEOE9cL4oPpHKf8YWjFIji64OYKUAHJVJnPWgsDN6t+/Kr4k04tREegkG2VL0RmQOzWiCPize6tM31uNpAn7h5fjHFlju5iEsRWElwZG7Q3+eJ3I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YoLJjHjk; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YoLJjHjk" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772633076; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=37JYngOeA4ilbnvJNnNil1+CpObDot6D//VD7RHfZ8Q=; b=YoLJjHjkfnUl/M3xKNzsRR26YDVtPJvPZIRVlcQM7QPtTskHt+6LSC+MP2uTqRx7qpyAPU rty9La6E7vP5aZElz5nZuR93mLpFeY5Ls2Oj7v8KOIB4kRkZJqAJ6umEWAzfLUiicNXDMj sEszEJX3htUtDAVko3I99Ng3H9eOW28= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-516-f9c12XnfNWiDXtK8o_9oOQ-1; Wed, 04 Mar 2026 09:04:30 -0500 X-MC-Unique: f9c12XnfNWiDXtK8o_9oOQ-1 X-Mimecast-MFC-AGG-ID: f9c12XnfNWiDXtK8o_9oOQ_1772633068 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3596F1800245; Wed, 4 Mar 2026 14:04:28 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.44.32.194]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 1B2C4195608E; Wed, 4 Mar 2026 14:04:22 +0000 (UTC) From: David Howells To: Matthew Wilcox , Christoph Hellwig , Jens Axboe , Leon Romanovsky Cc: David Howells , Christian Brauner , Paulo Alcantara , netfs@lists.linux.dev, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Paulo Alcantara , Steve French Subject: [RFC PATCH 07/17] netfs: Add a function to extract from an iter into a bvecq Date: Wed, 4 Mar 2026 14:03:14 +0000 Message-ID: <20260304140328.112636-8-dhowells@redhat.com> In-Reply-To: <20260304140328.112636-1-dhowells@redhat.com> References: <20260304140328.112636-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Add a function to extract a slice of data from an iterator of any type into a bvec queue chain. Signed-off-by: David Howells cc: Paulo Alcantara cc: Matthew Wilcox cc: Christoph Hellwig cc: Steve French cc: linux-cifs@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- fs/netfs/iterator.c | 122 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 ++ 2 files changed, 125 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index 72a435e5fc6d..faf4f0a3b33d 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,128 @@ #include #include "internal.h" +/** + * netfs_extract_iter - Extract the pages from an iterator into a bvecq + * @orig: The original iterator + * @orig_len: The amount of iterator to copy + * @max_segs: Maximum number of contiguous segments + * @fpos: Starting file position to label the bvecq with + * @_bvecq_head: Where to cache the bvec queue + * @extraction_flags: Flags to qualify the request + * + * Extract the page fragments from the given amount of the source iterator and + * build bvec queue that refers to all of those bits. This allows the original + * iterator to disposed of. + * + * @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA be + * allowed on the pages extracted. + * + * On success, the amount of data in the bvec is returned, the original + * iterator will have been advanced by the amount extracted. + * + * The bvecq segments are marked with indications on how to get clean up the + * extracted fragments. + */ +ssize_t netfs_extract_iter(struct iov_iter *orig, size_t orig_len, size_t max_segs, + unsigned long long fpos, struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags) +{ + struct bvecq *bq_tail = NULL; + ssize_t ret = 0; + size_t segs_per_bq; + size_t extracted = 0; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, orig_len); + + if (max_segs == 0) + max_segs = ULONG_MAX; + + /* We want the biggest pow-of-2 size that has at most 255 segs and that + * won't exceed a 4K page. + */ + segs_per_bq = (4096 - sizeof(*bq_tail)) / sizeof(bq_tail->__bv[0]); + if (segs_per_bq > 255) + segs_per_bq = (2048 - sizeof(*bq_tail)) / sizeof(bq_tail->__bv[0]); + + do { + struct bvecq *bq; + size_t nr_slots = iov_iter_npages(orig, umin(segs_per_bq, max_segs)); + + if (WARN_ON(nr_slots == 0 && extracted < orig_len) || + WARN_ON(nr_slots > max_segs)) + break; + max_segs -= nr_slots; + + bq = netfs_alloc_one_bvecq(nr_slots, GFP_NOFS); + if (!bq) { + ret = -ENOMEM; + break; + } + bq->free = user_backed_iter(orig); + bq->unpin = iov_iter_extract_will_pin(orig); + bq->prev = bq_tail; + bq->fpos = fpos + extracted; + + if (bq_tail) + bq_tail->next = bq; + else + *_bvecq_head = bq; + bq_tail = bq; + + if (extracted >= orig_len) + break; + + /* Put the page list at the end of the bvec list storage. bvec + * elements are larger than page pointers, so as long as we + * work 0->last, we should be fine. + */ + struct bio_vec *bv = bq->bv; + struct page **pages; + size_t bv_size = array_size(bq->max_segs, sizeof(*bv)); + size_t pg_size = array_size(bq->max_segs, sizeof(*pages)); + + pages = (void *)bv + bv_size - pg_size; + + do { + unsigned int cur_npages; + ssize_t got; + size_t offset; + + got = iov_iter_extract_pages(orig, &pages, orig_len - extracted, + bq->max_segs - bq->nr_segs, + extraction_flags, &offset); + if (got < 0) { + pr_err("Couldn't get user pages (rc=%zd)\n", got); + ret = got; + break; + } + + if (got > orig_len - extracted) { + pr_err("get_pages rc=%zd more than %zu\n", + got, orig_len - extracted); + break; + } + + extracted += got; + got += offset; + cur_npages = DIV_ROUND_UP(got, PAGE_SIZE); + + for (unsigned int i = 0; i < cur_npages; i++) { + size_t len = umin(got, PAGE_SIZE); + + bvec_set_page(&bq->bv[bq->nr_segs], + *pages++, len - offset, offset); + bq->nr_segs++; + got -= len; + offset = 0; + } + } while (extracted < orig_len && !bvecq_is_full(bq)); + } while (extracted < orig_len && max_segs > 0); + + return extracted ?: ret; +} +EXPORT_SYMBOL_GPL(netfs_extract_iter); + /** * netfs_extract_user_iter - Extract the pages from a user iterator into a bvec * @orig: The original iterator diff --git a/include/linux/netfs.h b/include/linux/netfs.h index f9ad067a0a0c..b146aeaaf6c9 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -448,6 +448,9 @@ void netfs_get_subrequest(struct netfs_io_subrequest *subreq, enum netfs_sreq_ref_trace what); void netfs_put_subrequest(struct netfs_io_subrequest *subreq, enum netfs_sreq_ref_trace what); +ssize_t netfs_extract_iter(struct iov_iter *orig, size_t orig_len, size_t max_segs, + unsigned long long fpos, struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags); ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, struct iov_iter *new, iov_iter_extraction_t extraction_flags);