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 DE53C3EC6B2 for ; Thu, 8 Oct 2026 08:47:58 +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=1791449280; cv=none; b=fjcncWa82XZi3RvJpPWiq+PEA/VRhvheWAu7jhLsAyF5LZsDgnAnaBrEES32fbty7ya+ks5zHZnFkz0hlgj0LckUZa94CHJ9Tbb3noIPPPM0GyFhvscwDp2WJIfk3uD6kwP39nbNkMlxGEIXlfCmWVfR8JicDxD2UxvghT8HAe4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791449280; c=relaxed/simple; bh=T54JJA+5Ow8ICg2lW4ppIawijxKWyfTSwHlKUS9F4U4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=c073PGSXldgqMCWhtNRj9OgZXcLDSYY5hT2uftPLItMxT+2Ex0K82tLnE101dMuwsyd7i8fdjE1hkNRPV9cmGLUTKon1cmOj+B5N3olusuSbRYIGXUhP6tBCC6/Uif6mIcqTYC4LJOyBex0qDiEsbwdkznYg7qefzO+74cO9GFc= 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=a3AsI6I7; 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="a3AsI6I7" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791449278; 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=wedgX4WrevLpzNepJP3YUsqGE7leHUHTlWrP39pl1QI=; b=a3AsI6I73KyKdEHFCnav9yuvltIq0s2fFy1ILMezBUnsr75Q3UFoLlx/ZibuyitFeD0c+4 hGcsE9cN4fe3M+o/6rIZ1Sup2Pe7GJji/HUwJoIcGiExlZesNniMO/R8KVHrFopFN5TEPz 4QwCZMGLHu3yJ+S4wSOLYgUFKd+dJaE= Received: from mx-prod-mc-03.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-553-qBKueqG3N2ejlFsjxYGAxw-1; Thu, 08 Oct 2026 04:47:53 -0400 X-MC-Unique: qBKueqG3N2ejlFsjxYGAxw-1 X-Mimecast-MFC-AGG-ID: qBKueqG3N2ejlFsjxYGAxw_1791449271 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 331831955EB6; Thu, 8 Oct 2026 08:47:51 +0000 (UTC) Received: from warthog.com (unknown [10.44.32.90]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 88D2A1956086; Thu, 8 Oct 2026 08:47:45 +0000 (UTC) From: David Howells To: Christian Brauner Cc: David Howells , Paulo Alcantara , Matthew Wilcox , Namjae Jeon , 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-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v16 2/8] netfs: Add a function to extract from an iter into a bvecq Date: Thu, 8 Oct 2026 09:47:14 +0100 Message-ID: <20261008084722.963948-3-dhowells@redhat.com> In-Reply-To: <20261008084722.963948-1-dhowells@redhat.com> References: <20261008084722.963948-1-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 10.30.177.12 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 Reviewed-by: Paulo Alcantara cc: Matthew Wilcox 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 31748526d568..8cf2efe0cd6c 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(min(max_pages, BVECQ_4KB_SLOTS), 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_EXTERNAL; + + if (bq_tail) + bvecq_append(bq_tail, bq); + else + *_bvecq_head = bq; + bq_tail = bq; + + 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)) { + /* Abandon what we got as very likely the + * overrun corrupted memory. + */ + 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 b0dd92d12a97..aca192bc5675 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -454,6 +454,9 @@ 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);