From patchwork Wed Apr 7 09:02:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12187511 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A6A3C433B4 for ; Wed, 7 Apr 2021 09:02:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BA3561363 for ; Wed, 7 Apr 2021 09:02:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346096AbhDGJCc (ORCPT ); Wed, 7 Apr 2021 05:02:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:33768 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231734AbhDGJCc (ORCPT ); Wed, 7 Apr 2021 05:02:32 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 94E5661205; Wed, 7 Apr 2021 09:02:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1617786142; bh=mCNxZr6PAXb88QQMAVew1Hy01FjFSgnQoftBuAIslDo=; h=From:To:Cc:Subject:Date:From; b=HUFGiDQ0kOeX/rPYOsocoeftnoReMRMnR0g3oNXj9x5Ip/O7KHW/nl6XD03YGf9Qr r2P7Ox6+R15wIbiF0QZWIlwUIJyi0UMm488mT2gE3A4DL/U/9mRhnaqeDeZgVbdWUw 7wuqZWLBnGPN/zW/cnEfvSXlm+8hG2kbeJzyYHMGC0h9dtas4SX0cEljzDBia5HDLU pAWW4Qtx2tyz0GoKUbhfPW+uanej5H8vCUql4AXZBZZBidj9Bs4XOa+OkYeTr5WSP9 1geiYpRcRZYTXJSMvb4GzIrxnEmmo3xzWoahqfl7XDwZEa4eC9qGPDK3dNgT3U+t0h cLpC/6tp/2gkw== From: Christian Brauner To: David Howells , linux-cachefs@redhat.com Cc: linux-fsdevel@vger.kernel.org, Amir Goldstein , Christian Brauner Subject: [PATCH v2 1/2] cachefiles: use private mounts in cache->mnt Date: Wed, 7 Apr 2021 11:02:07 +0200 Message-Id: <20210407090208.876920-1-brauner@kernel.org> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; i=eowlx1NntoC7VEw4p67kmsYshEbOr4Eu2ULNgq7j754=; m=2Fm9CC+jK5uAF6vPiYFh4E+Orhe2SMiIxerPMBwBPTs=; p=L7IxtciVyn3zbiHf6BWUkkC7t9WpxFa281SzqQqG28I=; g=6cd7f8f0c75a974e20e15df010a8c2fbf4973ef3 X-Patch-Sig: m=pgp; i=christian.brauner@ubuntu.com; s=0x0x91C61BC06578DCA2; b=iHUEABYKAB0WIQRAhzRXHqcMeLMyaSiRxhvAZXjcogUCYG11CAAKCRCRxhvAZXjcoiNyAP9tBY6 GnvzELlh16RMCQTiGcMxvhW0y5PG0ZyWg6wCf7wEAgi8owolgnSv/gI8jdW1mBxKpl/jMamImVDAL fLtecwI= Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Christian Brauner Since [1] we support creating private mounts from a given path's vfsmount. This makes them very suitable for any filesystem or filesystem functionality that piggybacks on paths of another filesystem. Overlayfs and ecryptfs (which I'll port next) are just two such examples. Without trying to imply to many similarities cachefiles have one thing in common with stacking filesystems namely that they also stack on top of existing paths. These paths are then used as caches for a netfs. Since private mounts aren't attached in the filesystem the aren't affected by mount property changes after cachefiles makes use of them. This seems a rather desirable property as the underlying path can't e.g. suddenly go from read-write to read-only and in general it means that cachefiles is always in full control of the underlying mount after the user has allowed it to be used as a cache (apart from operations that affect the superblock of course). Besides that - and probably irrelevant from the perspective of a cachefiles developer - it also makes things simpler for a variety of other vfs features. One concrete example is fanotify. When the path->mnt of the path that is used as a cache has been marked with FAN_MARK_MOUNT the semantics get tricky as it isn't clear whether the watchers of path->mnt should get notified about fsnotify events when files are created by cachefilesd via path->mnt. Using a private mount let's us elegantly handle this case too and aligns the behavior of stacks created by overlayfs. Reading through the codebase cachefiles currently takes path->mnt and stashes it in cache->mnt. Everytime a cache object needs to be created, looked-up, or in some other form interacted with cachefiles will create a custom path comprised of cache->mnt and the relevant dentry it is interested in: struct path cachefiles_path = { .mnt = cache->mnt, .dentry = dentry, }; So cachefiles already passes the cache->mnt through everywhere so supporting private mounts with cachefiles is pretty simply. Instead of recording path->mnt in cache->mnt we simply record a new private mount we created as a copy of path->mnt via clone_private_mount() in cache->mnt. The rest is cleanly handled by cachefiles already. I have tested this patch with afs: systemctl stop cachefilesd sudo mount --bind /var/cache/fscache /var/cache/fscache systemctl start cachefilesd sudo apt install kafs-client systemctl start afs.mount ls -al /afs ls -al /afs/grand.central.org/software/openafs/1.9.0 md5sum /afs/grand.central.org/software/openafs/1.9.0/openafs-1.9.0-doc.tar.bz2 cat /proc/fs/fscache/stats | grep [1-9] Cookies: idx=148 dat=34 spc=0 Objects: alc=40 nal=0 avl=40 ded=1 Pages : mrk=934 unc=203 Acquire: n=182 nul=0 noc=0 ok=182 nbf=0 oom=0 Lookups: n=40 neg=40 pos=0 crt=40 tmo=0 Retrvls: n=19 ok=0 wt=2 nod=19 nbf=0 int=0 oom=0 Retrvls: ops=19 owt=2 abt=0 Stores : n=934 ok=934 agn=0 nbf=0 oom=0 Stores : ops=21 run=955 pgs=934 rxd=934 olm=0 VmScan : nos=203 gon=0 bsy=0 can=0 wt=0 Ops : pend=2 run=40 enq=955 can=0 rej=0 Ops : ini=953 dfr=0 rel=953 gc=0 umount /afs/grand.central.org md5sum /afs/grand.central.org/software/openafs/1.9.0/openafs-1.9.0-doc.tar.bz2 cat /proc/fs/fscache/stats | grep [1-9] Cookies: idx=153 dat=58 spc=0 Objects: alc=68 nal=0 avl=68 ded=39 ChkAux : non=0 ok=24 upd=0 obs=0 Pages : mrk=1868 unc=934 Acquire: n=211 nul=0 noc=0 ok=211 nbf=0 oom=0 Lookups: n=68 neg=40 pos=28 crt=40 tmo=0 Relinqs: n=39 nul=0 wcr=0 rtr=0 Retrvls: n=38 ok=19 wt=3 nod=19 nbf=0 int=0 oom=0 Retrvls: ops=38 owt=2 abt=0 Stores : n=934 ok=934 agn=0 nbf=0 oom=0 Stores : ops=21 run=955 pgs=934 rxd=934 olm=0 VmScan : nos=203 gon=0 bsy=0 can=0 wt=0 Ops : pend=2 run=59 enq=955 can=0 rej=0 Ops : ini=972 dfr=0 rel=972 gc=0 [1]: c771d683a62e ("vfs: introduce clone_private_mount()") Cc: Amir Goldstein Cc: David Howells Cc: linux-cachefs@redhat.com Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- /* v2 */ Thank you to David for helping with testing! - David Howells : - Don't copy all of path into cache_path. Simply set both path.dentry and path.mnt to the desired values. - Check for idmapped mount before calling clone_private_mount(). - Add paragraphs into commit message to make it easier to parse. --- fs/cachefiles/bind.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) base-commit: a5e13c6df0e41702d2b2c77c8ad41677ebb065b3 diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c index 38bb7764b454..bbace3e51f52 100644 --- a/fs/cachefiles/bind.c +++ b/fs/cachefiles/bind.c @@ -81,7 +81,7 @@ int cachefiles_daemon_bind(struct cachefiles_cache *cache, char *args) static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) { struct cachefiles_object *fsdef; - struct path path; + struct path path, cache_path; struct kstatfs stats; struct dentry *graveyard, *cachedir, *root; const struct cred *saved_cred; @@ -115,16 +115,23 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) if (ret < 0) goto error_open_root; - cache->mnt = path.mnt; - root = path.dentry; - - ret = -EINVAL; if (mnt_user_ns(path.mnt) != &init_user_ns) { + ret = -EINVAL; + cache->mnt = NULL; pr_warn("File cache on idmapped mounts not supported"); goto error_unsupported; } + cache->mnt = clone_private_mount(&path); + if (IS_ERR(cache->mnt)) { + ret = PTR_ERR(cache->mnt); + cache->mnt = NULL; + pr_warn("Failed to create private mount for file cache\n"); + goto error_unsupported; + } + /* check parameters */ + root = path.dentry; ret = -EOPNOTSUPP; if (d_is_negative(root) || !d_backing_inode(root)->i_op->lookup || @@ -144,8 +151,10 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) if (ret < 0) goto error_unsupported; + cache_path.dentry = path.dentry; + cache_path.mnt = cache->mnt; /* get the cache size and blocksize */ - ret = vfs_statfs(&path, &stats); + ret = vfs_statfs(&cache_path, &stats); if (ret < 0) goto error_unsupported; @@ -229,7 +238,12 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) /* done */ set_bit(CACHEFILES_READY, &cache->flags); - dput(root); + + /* + * We've created a private mount and we've stashed our "cache" and + * "graveyard" dentries so we don't need the path anymore. + */ + path_put(&path); pr_info("File cache on %s registered\n", cache->cache.identifier); @@ -242,11 +256,11 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) dput(cache->graveyard); cache->graveyard = NULL; error_unsupported: + path_put(&path); mntput(cache->mnt); cache->mnt = NULL; dput(fsdef->dentry); fsdef->dentry = NULL; - dput(root); error_open_root: kmem_cache_free(cachefiles_object_jar, fsdef); error_root_object: