From patchwork Mon Mar 30 14:43:19 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 11465737 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 C4E2B159A for ; Mon, 30 Mar 2020 14:43:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A32F82073B for ; Mon, 30 Mar 2020 14:43:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hooEDvFm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728500AbgC3On2 (ORCPT ); Mon, 30 Mar 2020 10:43:28 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:51552 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727717AbgC3On2 (ORCPT ); Mon, 30 Mar 2020 10:43:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585579405; 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: references:references; bh=NdgMqytT/5K4fWVCzOyE8JxSDEeceY1fzG9HXeCbrkk=; b=hooEDvFm5LciiR3YW0MERM50+QXjDSJXREFODC6bEPjcN6bLdvsqubdh/SS18ulpgamSse WIt+6zTR4/Mt5MC1kra7K8Y8D9cgcs3Df+k5GysEOy7Ywr2YKgjGF+njfKCsiYgdGvNnIo pNMCShobKO3MTfgmag8vAbsCR+fT6XA= 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-4-YVz-3ff2PpyuvdN5ojGHlw-1; Mon, 30 Mar 2020 10:43:24 -0400 X-MC-Unique: YVz-3ff2PpyuvdN5ojGHlw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C349F1005513; Mon, 30 Mar 2020 14:43:22 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-112-66.rdu2.redhat.com [10.10.112.66]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0EDC7CFEA; Mon, 30 Mar 2020 14:43:19 +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 From: David Howells References: <1445647.1585576702@warthog.procyon.org.uk> To: torvalds@linux-foundation.org Cc: dhowells@redhat.com, viro@zeniv.linux.org.uk, dray@redhat.com, kzak@redhat.com, mszeredi@redhat.com, swhiteho@redhat.com, jlayton@redhat.com, raven@themaw.net, andres@anarazel.de, christian.brauner@ubuntu.com, keyrings@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [GIT PULL] fsinfo: Filesystem information query MIME-Version: 1.0 Content-ID: <1450011.1585579399.1@warthog.procyon.org.uk> Date: Mon, 30 Mar 2020 15:43:19 +0100 Message-ID: <1450012.1585579399@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@vger.kernel.org Hi Linus, If you could consider pulling this - or would you prefer it to go through Al? It adds a system call, fsinfo(), that allows information about the VFS, mount topology, superblock and files to be retrieved. This based on top of the mount and superblock notifications patchset and allows event counters implemented in the latter to be retrieved to allow overruns to be efficiently managed. I've excluded the Ext4 and NFS sample code from this pull request that I've previously included in my posted patchsets. ======= THE WHY ======= Why do we want this? Using /proc/mounts (or similar) has problems: (1) Reading from it holds a global lock (namespace_sem) that prevents mounting and unmounting. Lots of data is encoded and mangled into text whilst the lock is held, including superblock option strings and mount point paths. This causes performance problems when there are a lot of mount objects in a system. (2) Even though namespace_sem is held during a read, reading the whole file isn't necessarily atomic with respect to mount-type operations. If a read isn't satisfied in one go, then it may return to userspace briefly and then continue reading some way into the file. But changes can occur in the interval that may then go unseen. (3) Determining what has changed means parsing and comparing consecutive outputs of /proc/mounts. (4) Querying a specific mount or superblock means searching through /proc/mounts and searching by path or mount ID - but we might have an fd we want to query. (5) Mount topology is not explicit. One must derive it manually by comparing entries. (6) Whilst you can poll() it for events, it only tells you that something changed in the namespace, not what or whether you can even see the change. To fix the notification issues, the preceding notifications patchset added mount watch notifications whereby you can watch for notifications in a specific mount subtree. The notification messages include the ID(s) of the affected mounts. To support notifications, however, we need to be able to handle overruns in the notification queue. I added a number of event counters to struct super_block and struct mount to allow you to pin down the changes, but there needs to be a way to retrieve them. Exposing them through /proc would require adding yet another /proc/mounts-type file. We could add per-mount directories full of attributes in sysfs, but that has issues also (see below). Adding an extensible system call interface for retrieving filesystem information also allows other things to be exposed: (1) Jeff Layton's error handling changes need a way to allow error event information to be retrieved. (2) Bits in masks returned by things like statx() and FS_IOC_GETFLAGS are actually 3-state { Set, Unset, Not supported }. It could be useful to provide a way to expose information like this[*]. (3) Limits of the numerical metadata values in a filesystem[*]. (4) Filesystem capability information[*]. Filesystems don't all have the same capabilities, and even different instances may have different capabilities, particularly with network filesystems where the set of may be server-dependent. Capabilities might even vary at file granularity - though possibly such information should be conveyed through statx() instead. (5) ID mapping/shifting tables in use for a superblock. (6) Filesystem-specific information. I need something for AFS so that I can do pioctl()-emulation, thereby allowing me to implement certain of the AFS command line utilities that query state of a particular file. This could also have application for other filesystems, such as NFS, CIFS and ext4. [*] In a lot of cases these are probably fixed and can be memcpy'd from static data. There's a further consideration: I want to make it possible to have fsconfig(fd, FSCONFIG_CMD_CREATE) be intercepted by a container manager such that the manager can supervise a mount attempted inside the container. The manager would be given an fd pointing to the fs_context struct and would then need some way to query it (fsinfo()) and modify it (fsconfig()). This could also be used to arbitrate user-requested mounts when containers are not in play. ================ DESIGN DECISIONS ================ (1) Information is partitioned into sets of attributes. (2) Attribute IDs are integers as they're fast to compare. (3) Attribute values are typed (struct, list of structs, string, opaque blob). They type is fixed for a particular attribute. (4) For structure types, the length is also a version. New fields can be tacked onto the end. (5) When copying a versioned struct to userspace, the core handles a version mismatch by truncating or zero-padding the data as necessary. None of this is seen by the filesystem. (6) The core handles all the buffering and buffer resizing. (7) The filesystem never gets any access to the userspace parameter buffer or result buffer. (8) "Meta" attributes can describe other attributes. ======== OVERVIEW ======== fsinfo() is a system call that allows information about the filesystem at a particular path point to be queried as a set of attributes. Attribute values are of four basic types: (1) Structure with version-dependent length (the length is the version). (2) Variable-length string. (3) List of structures (all the same length). (4) Opaque blob. Attributes can have multiple values either as a sequence of values or a sequence-of-sequences of values and all the values of a particular attribute must be of the same type. Values can be up to INT_MAX size, subject to memory availability. Note that the values of an attribute *are* allowed to vary between dentries within a single superblock, depending on the specific dentry that you're looking at, but the values still have to be of the type for that attribute. I've tried to make the interface as light as possible, so integer attribute ID rather than string and the core does all the buffer allocation and expansion and all the extensibility support work rather than leaving that to the filesystems. This means that userspace pointers are not exposed to the filesystem. fsinfo() allows a variety of information to be retrieved about a filesystem and the mount topology: (1) General superblock attributes: - Filesystem identifiers (UUID, volume label, device numbers, ...) - The limits on a filesystem's capabilities - Information on supported statx fields and attributes and IOC flags. - A variety single-bit flags indicating supported capabilities. - Timestamp resolution and range. - The amount of space/free space in a filesystem (as statfs()). - Superblock notification counter. (2) Filesystem-specific superblock attributes: - Superblock-level timestamps. - Cell name, workgroup or other netfs grouping concept. - Server names and addresses. (3) VFS information: - Mount topology information. - Mount attributes. - Mount notification counter. - Mount point path. (4) Information about what the fsinfo() syscall itself supports, including the type and struct size of attributes. The system is extensible: (1) New attributes can be added. There is no requirement that a filesystem implement every attribute. A helper function is provided to scan a list of attributes and a filesystem can have multiple such lists. (2) Version length-dependent structure attributes can be made larger and have additional information tacked on the end, provided it keeps the layout of the existing fields. If an older process asks for a shorter structure, it will only be given the bits it asks for. If a newer process asks for a longer structure on an older kernel, the extra space will be set to 0. In all cases, the size of the data actually available is returned. In essence, the size of a structure is that structure's version: a smaller size is an earlier version and a later version includes everything that the earlier version did. (3) New single-bit capability flags can be added. This is a structure-typed attribute and, as such, (2) applies. Any bits you wanted but the kernel doesn't support are automatically set to 0. fsinfo() may be called like the following, for example: struct fsinfo_params params = { .at_flags = AT_SYMLINK_NOFOLLOW, .flags = FSINFO_FLAGS_QUERY_PATH, .request = FSINFO_ATTR_AFS_SERVER_ADDRESSES, .Nth = 2, }; struct fsinfo_server_address address; len = fsinfo(AT_FDCWD, "/afs/grand.central.org/doc", ¶ms, &address, sizeof(address)); The above example would query an AFS filesystem to retrieve the address list for the 3rd server, and: struct fsinfo_params params = { .at_flags = AT_SYMLINK_NOFOLLOW, .flags = FSINFO_FLAGS_QUERY_PATH, .request = FSINFO_ATTR_NFS_SERVER_NAME; }; char server_name[256]; len = fsinfo(AT_FDCWD, "/home/dhowells/", ¶ms, &server_name, sizeof(server_name)); would retrieve the name of the NFS server as a string. In future, I want to make fsinfo() capable of querying a context created by fsopen() or fspick(), e.g.: fd = fsopen("ext4", 0); struct fsinfo_params params = { .flags = FSINFO_FLAGS_QUERY_FSCONTEXT, .request = FSINFO_ATTR_CONFIGURATION; }; char buffer[65536]; fsinfo(fd, NULL, ¶ms, &buffer, sizeof(buffer)); even if that context doesn't currently have a superblock attached. Thanks, David --- The following changes since commit 8dbf1aa122da5bbb4ede0f363a8a18dfc723be33: watch_queue: sample: Display superblock notifications (2020-03-19 17:31:09 +0000) are available in the Git repository at: git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git tags/fsinfo-20200330 for you to fetch changes up to 80f0ef902951fd3e7446767e7d37d543d936b72f: fsinfo: Add support for AFS (2020-03-19 17:31:34 +0000) ---------------------------------------------------------------- Filesystem information ---------------------------------------------------------------- David Howells (11): fsinfo: Add fsinfo() syscall to query filesystem information fsinfo: Provide a bitmap of supported features fsinfo: Allow retrieval of superblock devname, options and stats fsinfo: Allow fsinfo() to look up a mount object by ID fsinfo: Add a uniquifier ID to struct mount fsinfo: Allow mount information to be queried fsinfo: Allow mount topology and propagation info to be retrieved fsinfo: Provide notification overrun handling support fsinfo: sample: Mount listing program fsinfo: Add API documentation fsinfo: Add support for AFS Documentation/filesystems/fsinfo.rst | 574 +++++++++++++++++++ arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/Kconfig | 7 + fs/Makefile | 1 + fs/afs/internal.h | 1 + fs/afs/super.c | 218 +++++++- fs/d_path.c | 2 +- fs/fsinfo.c | 725 ++++++++++++++++++++++++ fs/internal.h | 14 + fs/mount.h | 3 + fs/mount_notify.c | 2 + fs/namespace.c | 389 ++++++++++++- include/linux/fs.h | 4 + include/linux/fsinfo.h | 111 ++++ include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 4 +- include/uapi/linux/fsinfo.h | 326 +++++++++++ include/uapi/linux/mount.h | 10 +- kernel/sys_ni.c | 1 + samples/vfs/Makefile | 7 + samples/vfs/test-fsinfo.c | 818 ++++++++++++++++++++++++++++ samples/vfs/test-mntinfo.c | 279 ++++++++++ 39 files changed, 3511 insertions(+), 9 deletions(-) create mode 100644 Documentation/filesystems/fsinfo.rst create mode 100644 fs/fsinfo.c create mode 100644 include/linux/fsinfo.h create mode 100644 include/uapi/linux/fsinfo.h create mode 100644 samples/vfs/test-fsinfo.c create mode 100644 samples/vfs/test-mntinfo.c