From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valerie Aurora Subject: [PATCH 18/34] union-mount: Create check_topmost_union_mnt() Date: Thu, 16 Sep 2010 15:12:09 -0700 Message-ID: <1284675145-4391-19-git-send-email-vaurora@redhat.com> References: <1284675145-4391-1-git-send-email-vaurora@redhat.com> Cc: Miklos Szeredi , Christoph Hellwig , Andreas Gruenbacher , Nick Piggin , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Valerie Aurora To: Alexander Viro Return-path: In-Reply-To: <1284675145-4391-1-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org check_topmost_union_mnt() checks that the topmost layer of a proposed union mount is read-write, supports fallthrus and whiteouts, and isn't mounted elsewhere. Signed-off-by: Valerie Aurora --- fs/namespace.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 files changed, 40 insertions(+), 0 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index ffa5ed7..62c2f7a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1353,6 +1353,46 @@ static int invent_group_ids(struct vfsmount *mnt, bool recurse) return 0; } +/** + * check_topmost_union_mnt - mount-time checks for union mount + * + * @topmost_mnt: vfsmount of the topmost union filed system + * @mnt_flags: mount flags for the topmost mount + * + * Our readdir() solution of copying up directory entries requires + * that the topmost layer be writeable and support whiteouts and + * fallthrus. The topmost file system can't be mounted elsewhere + * because it's Too Hard(tm). + */ + +static int check_topmost_union_mnt(struct vfsmount *topmost_mnt, int mnt_flags) +{ + struct super_block *sb = topmost_mnt->mnt_sb; +#ifndef CONFIG_UNION_MOUNT + printk(KERN_INFO "union mount: not supported by the kernel\n"); + return -EINVAL; +#endif + if (mnt_flags & MNT_READONLY) + return -EROFS; + + if (atomic_read(&sb->s_active) != 1) { + printk(KERN_INFO "union mount: topmost fs mounted elsewhere\n"); + return -EBUSY; + } + + if (!(sb->s_flags & MS_WHITEOUT)) { + printk(KERN_INFO "union mount: whiteouts not supported by fs\n"); + return -EINVAL; + } + + if (!(sb->s_flags & MS_FALLTHRU)) { + printk(KERN_INFO "union mount: fallthrus not supported by fs\n"); + return -EINVAL; + } + + return 0; +} + /* * @source_mnt : mount tree to be attached * @nd : place the mount tree @source_mnt is attached -- 1.6.3.3