From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 857014921AD for ; Mon, 8 Jun 2026 14:56:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780930581; cv=none; b=VWyAtZonc7I8Pb8bF1jL/FUXUuDsksw7AJsj9VNokSU4n/fKy5E2vCiV/5p59lYaEg7LN7sI9jXr9VYqA46vjssbagzUROFoRNqBpyhIYeJ7Y0IaKC2n4SldFnUUeVCpJv+yN82Bv3bgv/H8nyADhr/vjZlSLLhhm5x0K+8ZmJM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780930581; c=relaxed/simple; bh=q0nHBdS8B0gFtMjCdDHzxTp81+J/3i877MqD45cDrfk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:content-type; b=tu7PEi4SsO0oFJwTc/llqSBo4BERolbn3ZoZL2rUnnSYN8lfSX2V4dpLMAU6yAjMxp1j7LImWMAV1QI9etIib6wijU3ZMfi4D++D5vqSpeI9u37JXeZpaQmg4v2Wsrd/gRryQjE+AGsu3UTMq1X5sm5kI99Itgw1yDniH7aHFCM= 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=Bsfl11jd; arc=none smtp.client-ip=170.10.129.124 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="Bsfl11jd" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780930577; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vbkc2ThYu5P21iahS6kl0ozQ9hmor5lbvUCQK6sK6n0=; b=Bsfl11jd+gpGjZZ9y1S/9GbIhNavbdo+VZkYsW9dNGgJPaIe9TCjtEd00GX0625tsNzcul XPcrRhsORiZbvNIYogBepQCWz3O/zMjrKDXZByIZeAi71XVF/11qpOVkZNtjBGVYqnreQm Q85eaRu/APUOcfbKLm4CMZ9HpUzb65g= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-449-JtDZMFVCO924HqhQ9bPR9w-1; Mon, 08 Jun 2026 10:56:14 -0400 X-MC-Unique: JtDZMFVCO924HqhQ9bPR9w-1 X-Mimecast-MFC-AGG-ID: JtDZMFVCO924HqhQ9bPR9w_1780930571 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 67CD0195607A; Mon, 8 Jun 2026 14:56:11 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.44.32.43]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 4F8493008B35; Mon, 8 Jun 2026 14:56:05 +0000 (UTC) From: David Howells To: Christian Brauner , Matthew Wilcox , Christoph Hellwig Cc: David Howells , Paulo Alcantara , Jens Axboe , Leon Romanovsky , Steve French , ChenXiaoSong , Marc Dionne , Eric Van Hensbergen , Dominique Martinet , Ilya Dryomov , Trond Myklebust , 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-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 10/22] netfs: Add a function to extract from an iter into a bvecq Date: Mon, 8 Jun 2026 15:54:18 +0100 Message-ID: <20260608145432.681865-11-dhowells@redhat.com> In-Reply-To: <20260608145432.681865-1-dhowells@redhat.com> References: <20260608145432.681865-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: netfs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-MFC-PROC-ID: wfad3tYpuqOkOc5siArIozk717I12TPXk8cIQfPF0Os_1780930571 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true 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 | 125 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 + 2 files changed, 128 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index b375567e0520..d2c3055a488c 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,131 @@ #include #include "internal.h" +/** + * netfs_extract_iter - Extract virtually contiguous pages from an iterator into a bvecq + * @orig: The original iterator + * @max_len: Maximum number of bytes to extract + * @max_pages: Maximum number of pages to extract + * @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 virtually contiguous page fragments from the source iterator up to + * the given maxima 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 max_len, size_t max_pages, + 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 extracted = 0; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, max_len); + + if (max_len > orig->count) + max_len = orig->count; + if (WARN_ON_ONCE(!max_len || !max_pages)) + return 0; + + max_pages = iov_iter_npages(orig, max_pages); + if (!max_pages) + return 0; + + do { + struct bvecq *bq; + + bq = bvecq_alloc_one(max_pages, GFP_NOFS); + if (!bq) { + ret = -ENOMEM; + break; + } + if (user_backed_iter(orig)) + bq->mem_type = iov_iter_extract_will_pin(orig) ? + BVECQ_MEM_GUP : BVECQ_MEM_PAGECACHE; + bq->prev = bq_tail; + bq->fpos = fpos + extracted; + + if (bq_tail) + bq_tail->next = bq; + else + *_bvecq_head = bq; + bq_tail = bq; + + if (max_len == 0) + break; + + struct bio_vec *bv = bq->bv; + do { + struct page **pages; + ssize_t got; + size_t offset; + size_t space = bq->max_slots - bq->nr_slots; + size_t bv_size = array_size(bq->max_slots, sizeof(*bv)); + size_t pg_size = array_size(space, sizeof(*pages)); + + /* 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. + */ + pages = (void *)bv + bv_size - pg_size; + + got = iov_iter_extract_pages(orig, &pages, max_len, + space, extraction_flags, &offset); + if (got < 0) { + ret = got; + goto out; + } + + if (got == 0) { + pr_err("extract_pages gave nothing from %zu, %zu\n", + extracted, max_len); + ret = -EIO; + goto out; + } + + if (WARN(got > max_len, + "%s: extract_pages overrun %zd > %zu bytes\n", + __func__, got, max_len)) { + ret = -EIO; + break; + } + + extracted += got; + max_len -= got; + + do { + size_t len = umin(got, PAGE_SIZE - offset); + + BUG_ON(bq->nr_slots >= bq->max_slots); + + bvec_set_page(&bq->bv[bq->nr_slots], + *pages++, len, offset); + bq->nr_slots++; + got -= len; + offset = 0; + } while (got > 0); + } while (max_len > 0 && !bvecq_is_full(bq)); + + max_pages -= bq->nr_slots; + } while (max_len > 0 && max_pages > 0); + +out: + 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 12e5c51c11c8..40f45ecf1db8 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -460,6 +460,9 @@ 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 max_len, size_t max_pages, + 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);