From patchwork Fri Aug 7 15:06:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 11705807 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BD5EE722 for ; Fri, 7 Aug 2020 15:06:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9CD292075D for ; Fri, 7 Aug 2020 15:06:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="DcmzLv/K" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726212AbgHGPGZ (ORCPT ); Fri, 7 Aug 2020 11:06:25 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:57647 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726202AbgHGPGY (ORCPT ); Fri, 7 Aug 2020 11:06:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596812781; 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; bh=uTzSeO9LJ/fgrO0vB/deWP/c4fURGdv9ZVO/IS4V2IA=; b=DcmzLv/K8aYRHR/cMfPpSZMZpVH7FB12ShKcMSXyfmdgRT34Tm3HmeV2O4iz9e0I2aRrav E1ilx9+4zibAChh10wAHZ/BW5C6XFsWUyyX4GCS3dsgfWOzVxwxfAKPOYs/whniK4woR4I gzYwlt4c8EC1BRrPi34ES9v43Q9RsIo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-159-v6HwMxBdOUW-40cqebJcUg-1; Fri, 07 Aug 2020 11:06:20 -0400 X-MC-Unique: v6HwMxBdOUW-40cqebJcUg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A3821100AA21; Fri, 7 Aug 2020 15:06:18 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-113-69.rdu2.redhat.com [10.10.113.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id 00FC05D9D5; Fri, 7 Aug 2020 15:06:16 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 1/2] Add a manpage for watch_queue(7) From: David Howells To: mtk.manpages@gmail.com Cc: torvalds@linux-foundation.org, dhowells@redhat.com, keyrings@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 07 Aug 2020 16:06:16 +0100 Message-ID: <159681277616.35436.11229310534842613599.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@vger.kernel.org Add a manual page for the notifications/watch_queue facility. Signed-off-by: David Howells --- man7/watch_queue.7 | 285 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 285 insertions(+) create mode 100644 man7/watch_queue.7 diff --git a/man7/watch_queue.7 b/man7/watch_queue.7 new file mode 100644 index 000000000..6b22ad689 --- /dev/null +++ b/man7/watch_queue.7 @@ -0,0 +1,285 @@ +.\" +.\" Copyright (C) 2020 Red Hat, Inc. All Rights Reserved. +.\" Written by David Howells (dhowells@redhat.com) +.\" +.\" This program is free software; you can redistribute it and/or +.\" modify it under the terms of the GNU General Public Licence +.\" as published by the Free Software Foundation; either version +.\" 2 of the Licence, or (at your option) any later version. +.\" +.TH WATCH_QUEUE 7 "2020-08-07" Linux "General Kernel Notifications" +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH NAME +General kernel notification queue +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH SYNOPSIS +#include +.EX + +pipe2(fds, O_NOTIFICATION_PIPE); +ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, max_message_count); +ioctl(fds[0], IOC_WATCH_QUEUE_SET_FILTER, &filter); +keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fds[0], 0x01); +for (;;) { + buf_len = read(fds[0], buffer, sizeof(buffer)); + ... +} +.EE +.SH OVERVIEW +.PP +The general kernel notification queue is a general purpose transport for kernel +notification messages to userspace. Notification messages are marked with type +information so that events from multiple sources can be distinguished. +Messages are also of variable length to accommodate different information for +each type. +.PP +Queues are implemented on top of standard pipes and multiple independent queues +can be created. After a pipe has been created, its size and filtering can be +configured and event sources attached. The pipe can then be read or polled to +wait for messages. +.PP +Multiple messages may be read out of the queue at a time if the buffer is large +enough, but messages will not get split amongst multiple reads. If the buffer +isn't large enough for a message, +.B ENOBUFS +will be returned. +.PP +In the case of message loss, +.BR read (2) +will fabricate a loss message and pass that to userspace immediately after the +point at which the loss occurred. +.PP +A notification pipe allocates a certain amount of locked kernel memory (so that +the kernel can write a notification into it from contexts where allocation is +restricted), and so is subject to pipe resource limit restrictions. +.PP +Sources must be attached to a queue manually; there's no single global event +source, but rather a variety of sources, each of which can be attached to by +multiple queues. Attachments can be set up by: +.TP +.BR keyctl_watch_key (3) +Monitor a key or keyring for changes. +.PP +Because a source can produce a lot of different events, not all of which may be +of interest to the watcher, a filter can be set on a queue to determine whether +a particular event will get inserted in a queue at the point of posting inside +the kernel. + +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH MESSAGE STRUCTURE +.PP +The output from reading the pipe is divided into variable length messages. +Read will never split a message across two separate read calls. Each message +begins with a header of the form: +.PP +.in +4n +.EX +struct watch_notification { + __u32 type:24; + __u32 subtype:8; + __u32 info; +}; +.EE +.in +.PP +Where +.I type +indicates the general class of notification, +.I subtype +indicates the specific type of notification within that class and +.I info +includes the message length (in bytes), the watcher's ID and some type-specific +information. +.PP +A special message type, +.BR WATCH_TYPE_META , +exists to convey information about the notification facility itself. It has a +number of subtypes: +.TP +.B WATCH_META_LOSS_NOTIFICATION +This indicates one or more messages were lost, probably due to a buffer +overrun. +.TP +.B WATCH_META_REMOVAL_NOTIFICATION +This indicates that a notification source went away whilst it is being watched. +This comes in two lengths: a short variant that carries just the header and a +long variant that includes a 64-bit identifier as well that identifies the +source more precisely (which variant is used and how the identifier should be +interpreted is source dependent). +.PP +.I info +includes the following fields: +.TP +.B WATCH_INFO_LENGTH +Bits 0-6 indicate the size of the message in bytes, and can be between 8 and +127. +.TP +.B WATCH_INFO_ID +Bits 8-15 indicate the tag given to the source binding call. This is a number +between 0 and 255 and is purely a source index for userspace's use and isn't +interpreted by the kernel. +.TP +.B WATCH_INFO_TYPE_INFO +Bits 16-31 indicate subtype-dependent information. + +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH IOCTL COMMANDS +Pipes opened O_NOTIFICATION_PIPE have the following +.IR ioctl () +commands available: +.TP +.B IOC_WATCH_QUEUE_SET_SIZE +The ioctl argument is indicates the maximum number of messages that can be +inserted into the pipe. This must be a power of two. This command also +pre-allocates memory to hold messages. +.IP +This may only be done once and the queue cannot be used until this command has +been done. +.TP +.B IOC_WATCH_QUEUE_SET_FILTER +This is used to set filters on the notifications that get written into the +buffer. The ioctl argument points to a structure of the following form: +.IP +.in +4n +.EX +struct watch_notification_filter { + __u32 nr_filters; + __u32 __reserved; + struct watch_notification_type_filter filters[]; +}; +.EE +.in +.IP +Where +.I nr_filters +indicates the number of elements in the +.IR filters [] +array. Each element in the filters array specifies a filter and is of the +following form: +.IP +.in +4n +.EX +struct watch_notification_type_filter { + __u32 type; + __u32 info_filter; + __u32 info_mask; + __u32 subtype_filter[8]; +}; +.EE +.in +.IP +Where +.I type +refer to the type field in a notification record header, info_filter and +info_mask refer to the info field and subtype_filter is a bit-mask of subtypes. +.IP +If no filters are installed, all notifications are allowed by default and if +one or more filters are installed, notifications are disallowed by default. +.IP +A notifications matches a filter if, for notification N and filter F: +.IP +.in +4n +.EX +N->type == F->type && +(F->subtype_filter[N->subtype >> 5] & + (1U << (N->subtype & 31))) && +(N->info & F->info_mask) == F->info_filter) +.EE +.in +.IP + + +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH EXAMPLE +To use the notification mechanism, first of all the pipe has to be opened and +the size must be set: +.PP +.in +4n +.EX +int fds[2]; +pipe2(fd[0], O_NOTIFICATION_QUEUE); +int wfd = fd[0]; + +ioctl(wfd, IOC_WATCH_QUEUE_SET_SIZE, 16); +.EE +.in +.PP +From this point, the queue is open for business. Filters can be set to +restrict the notifications that get inserted into the buffer from the sources +that are being watched. For example: +.PP +.in +4n +.EX +static struct watch_notification_filter filter = { + .nr_filters = 1, + .__reserved = 0, + .filters = { + [0] = { + .type = WATCH_TYPE_KEY_NOTIFY, + .subtype_filter[0] = 1 << NOTIFY_KEY_LINKED, + .info_filter = 1 << WATCH_INFO_FLAG_2, + .info_mask = 1 << WATCH_INFO_FLAG_2, + }, + }, +}; + +ioctl(wfd, IOC_WATCH_QUEUE_SET_FILTER, &filter); +.EE +.in +.PP +will only allow key-change notifications that indicate a key is linked into a +keyring and then only if type-specific flag WATCH_INFO_FLAG_2 is set on the +notification. +.PP +Sources can then be watched, for example: +.PP +.in +4n +.EX +keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, wfd, 0x33); +.EE +.in +.PP +The first places a watch on the process's session keyring, directing the +notifications to the buffer we just created and specifying that they should be +tagged with 0x33 in the info ID field. +.PP +When it is determined that there is something in the buffer, messages can be +read out of the ring with something like the following: +.PP +.in +4n +.EX +for (;;) { + unsigned char buf[128]; + read(fd, buf, sizeof(buf)); + struct watch_notification *n = (struct watch_notification *)buf; + switch (n->type) { + case WATCH_TYPE_META: + switch (n->subtype) { + case WATCH_META_REMOVAL_NOTIFICATION: + saw_removal_notification(n); + break; + case WATCH_META_LOSS_NOTIFICATION: + printf("-- LOSS --\n"); + break; + } + break; + case WATCH_TYPE_KEY_NOTIFY: + saw_key_change(n); + break; + } +} +.EE +.in +.PP + +.\""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" +.SH VERSIONS +The notification queue driver first appeared in v5.8 of the Linux kernel. +.SH SEE ALSO +.ad l +.nh +.BR keyctl (1), +.BR ioctl (2), +.BR pipe2 (2), +.BR read (2), +.BR keyctl_watch_key (3) From patchwork Fri Aug 7 15:06:23 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 11705813 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2D726722 for ; Fri, 7 Aug 2020 15:06:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 098972075D for ; Fri, 7 Aug 2020 15:06:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="G+Lf+Mji" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726569AbgHGPGd (ORCPT ); Fri, 7 Aug 2020 11:06:33 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:23092 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726563AbgHGPGb (ORCPT ); Fri, 7 Aug 2020 11:06:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596812789; 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=O53y8SXTHe8UM7SjU5jL95IZsuNLkUIcYidxItMzlrY=; b=G+Lf+MjijdMIJx+Fl+7pJ5hRIaLsN3B7fqHP8coErL2Fzw7u9qiZbucAD3L7IeoiiGluT6 cpzNeEFqdmCLMvr2QQzj/1hq99bRRc/afwtxod9FImdm0oYViqTp1QF2Ev/drdZeq+pMSy QxZtPpDXawJWvs/Lv7Z4qm9nZpNIueI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-347-CIFLLUNGM1azCEZB4JLG0g-1; Fri, 07 Aug 2020 11:06:27 -0400 X-MC-Unique: CIFLLUNGM1azCEZB4JLG0g-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 19D4579EC0; Fri, 7 Aug 2020 15:06:26 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-113-69.rdu2.redhat.com [10.10.113.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id A9C3760CD0; Fri, 7 Aug 2020 15:06:24 +0000 (UTC) Organization: Red Hat UK Ltd. 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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 2/2] Modify the pipe(2) manpage for notification queues From: David Howells To: mtk.manpages@gmail.com Cc: torvalds@linux-foundation.org, dhowells@redhat.com, keyrings@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 07 Aug 2020 16:06:23 +0100 Message-ID: <159681278389.35436.15823690384983762521.stgit@warthog.procyon.org.uk> In-Reply-To: <159681277616.35436.11229310534842613599.stgit@warthog.procyon.org.uk> References: <159681277616.35436.11229310534842613599.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@vger.kernel.org Modify the pipe(2) manual page to cover support for notification queues Signed-off-by: David Howells --- man2/pipe.2 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/man2/pipe.2 b/man2/pipe.2 index 117f8950c..c50b38530 100644 --- a/man2/pipe.2 +++ b/man2/pipe.2 @@ -146,6 +146,13 @@ referred to by the new file descriptors. Using this flag saves extra calls to .BR fcntl (2) to achieve the same result. +.TP +.B O_NOTIFICATION_PIPE +This enables use of the pipe as a notification transport (see +.BR watch_queue (7) +for more information). When a pipe is in this mode, it may not be spliced as +the insertion of notification messages into the pipe buffer can happen +asynchronously and may cause splice to malfunction. .SH RETURN VALUE On success, zero is returned. On error, \-1 is returned, @@ -292,4 +299,5 @@ main(int argc, char *argv[]) .BR vmsplice (2), .BR write (2), .BR popen (3), -.BR pipe (7) +.BR pipe (7), +.BR watch_queue (7)