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 E338C444717 for ; Mon, 24 Aug 2026 14:43:47 +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=1787582632; cv=none; b=WTsGBecgnE+U7M91KuNaEJCjV0Sup78sDHVVn4DQSOKQ/ZpRu/tK+VWqMKsw4xatjlJGaFqt58uT8cVHhndkEgWxZ7ptAlr9YOQ4NYVsLymKMIM4ysz2lHWz3sUUXVuhqCSssepepjXBhV5IbkMYBMh+0bJz3+svIyC4f5Pr+2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787582632; c=relaxed/simple; bh=6xHWjsY1qDBoefXHrGBW8eWcOhqLBMGbASXLWlznntE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=J3KtxC7bqAsLrh0KDV62/PW7EgMz99S487Sf+JPnMewLexBtQaWZO7eZmfc3xMun1IHFU2vMjbaxx4bax/hOe80Ig/nQU8d6EHbBdl7oxTIjxNo+laqur3quxH1bKlCa+kTbHKcN9EcYN2k8Bll8BwUA4/5vxm+YViVGudQnFMU= 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=XZx8fdiA; 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="XZx8fdiA" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1787582624; 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=5t4/4PShxGf/yJwbsS+IUPK4M6t7DCNTTfTNINUpLpc=; b=XZx8fdiAkus/9c+SEsnMIKPVPECuvkLkfcNkI/li1fm45z6YYnBtAfxSwaRJUbUXjmQxNl B4ZnuR5XI8Q5LxlZraFDkoqXCCY+1NgmLTfPvHm4wOr29yrzJ6Zk1fheoxSaUBiT+4J+U6 IbXiZNPI6CrLQnLyUE70mHmNPnMSods= Received: from mx-prod-mc-08.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-26-t_D96OY9MSi7wj8RCirzKA-1; Mon, 24 Aug 2026 10:43:38 -0400 X-MC-Unique: t_D96OY9MSi7wj8RCirzKA-1 X-Mimecast-MFC-AGG-ID: t_D96OY9MSi7wj8RCirzKA_1787582614 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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C6A4E18303C5; Mon, 24 Aug 2026 14:43:34 +0000 (UTC) Received: from warthog.com (unknown [10.44.32.15]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id A2D341955DAA; Mon, 24 Aug 2026 14:43:28 +0000 (UTC) From: David Howells To: Paulo Alcantara Cc: David Howells , Christian Brauner , Matthew Wilcox , Christoph Hellwig , Jens Axboe , Leon Romanovsky , Namjae Jeon , ChenXiaoSong , Marc Dionne , Stefan Metzmacher , Eric Van Hensbergen , Dominique Martinet , Ilya Dryomov , 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 v10 13/35] netfs: Add a function to extract from an iter into a bvecq Date: Mon, 24 Aug 2026 15:41:06 +0100 Message-ID: <20260824144130.759997-14-dhowells@redhat.com> In-Reply-To: <20260824144130.759997-1-dhowells@redhat.com> References: <20260824144130.759997-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@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: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- fs/netfs/iterator.c | 143 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 + 2 files changed, 146 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index eb1efb17f53a..e66c589ca3b0 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,149 @@ #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 + * @_bvecq_head: Where to cache the bvec queue + * @extraction_flags: Flags to qualify the request + * @gfp: Allocation mode for bvecq structs. + * + * 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 or partial success, the amount of data in the bvec is returned, + * the original iterator will have been advanced by the amount extracted. + * + * If an error occurs and no pages are extracted, an error will be returned and + * any allocated bvecq will be freed. If there is no data to be extracted (or + * @max_len or @max_pages are zero), a single empty bvecq will be returned. + * + * 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, + struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags, gfp_t gfp) +{ + struct bvecq *bq_tail = NULL, *bq; + ssize_t ret = 0; + size_t extracted = 0; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, max_len); + + *_bvecq_head = NULL; + if (max_len > orig->count) + max_len = orig->count; + if (!max_len || !max_pages) + goto alloc_empty; + if (WARN_ON_ONCE(max_pages > INT_MAX)) + max_pages = INT_MAX; /* Protect iov_iter_npages(). */ + + max_pages = iov_iter_npages(orig, max_pages); + if (!max_pages) + goto alloc_empty; + + do { + bq = bvecq_alloc_one(max_pages, gfp, false); + 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; + + if (bq_tail) + bvecq_append(bq_tail, bq); + else + *_bvecq_head = bq; + bq_tail = bq; + + if (max_len == 0) + break; + + struct bio_vec *bv = bq->bv; + unsigned int slot = 0; + do { + struct page **pages; + ssize_t got; + size_t offset; + size_t space = bq->max_slots - slot; + 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, + min(space, max_pages), + extraction_flags, &offset); + if (got < 0) { + ret = got; + goto out; + } + + if (got == 0) { + pr_err("extract_pages gave nothing from %zx, %zx\n", + extracted, max_len); + ret = -EIO; + goto out; + } + + if (WARN(got > max_len, + "%s: extract_pages overrun %zx > %zx bytes\n", + __func__, got, max_len)) { + ret = -EIO; + goto out; + } + + extracted += got; + max_len -= got; + + do { + size_t len = umin(got, PAGE_SIZE - offset); + + BUG_ON(slot >= bq->max_slots); + + bvec_set_page(&bq->bv[slot], *pages++, len, offset); + slot++; + max_pages--; + got -= len; + offset = 0; + } while (got > 0); + + bvecq_filled_to(bq, slot); + } while (max_len > 0 && max_pages > 0 && !bvecq_is_full(bq)); + + } while (max_len > 0 && max_pages > 0); + +out: + if (extracted || ret == 0) + return extracted; + bvecq_put(*_bvecq_head); + *_bvecq_head = NULL; + return ret; + +alloc_empty: + bq = bvecq_alloc_one(1, gfp, false); + if (!bq) + return -ENOMEM; + *_bvecq_head = bq; + return 0; + +} +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 c0eb80e49f5c..14a24bb80af5 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -431,6 +431,9 @@ 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, + struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags, gfp_t gfp); ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, struct iov_iter *new, iov_iter_extraction_t extraction_flags);