Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761063AbXKAXKx (ORCPT ); Thu, 1 Nov 2007 19:10:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756081AbXKAXIn (ORCPT ); Thu, 1 Nov 2007 19:08:43 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:33807 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755508AbXKAXIl (ORCPT ); Thu, 1 Nov 2007 19:08:41 -0400 Subject: [PATCH 06/27] r-o-bind-mounts-stub-functions To: akpm@osdl.org Cc: linux-kernel@vger.kernel.org, miklos@szeredi.hu, hch@infradead.org, Dave Hansen From: Dave Hansen Date: Thu, 01 Nov 2007 16:08:34 -0700 References: <20071101230826.9A4F6E00@kernel> In-Reply-To: <20071101230826.9A4F6E00@kernel> Message-Id: <20071101230834.012D6939@kernel> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3804 Lines: 107 This patch adds two function mnt_want_write() and mnt_drop_write(). These are used like a lock pair around and fs operations that might cause a write to the filesystem. Before these can become useful, we must first cover each place in the VFS where writes are performed with a want/drop pair. When that is complete, we can actually introduce code that will safely check the counts before allowing r/w<->r/o transitions to occur. Signed-off-by: Dave Hansen Cc: Christoph Hellwig Signed-off-by: Andrew Morton Acked-by: Serge Hallyn --- linux-2.6.git-dave/fs/namespace.c | 54 +++++++++++++++++++++++++++++++ linux-2.6.git-dave/include/linux/mount.h | 3 + 2 files changed, 57 insertions(+) diff -puN fs/namespace.c~r-o-bind-mounts-stub-functions fs/namespace.c --- linux-2.6.git/fs/namespace.c~r-o-bind-mounts-stub-functions 2007-11-01 14:46:08.000000000 -0700 +++ linux-2.6.git-dave/fs/namespace.c 2007-11-01 14:46:08.000000000 -0700 @@ -77,6 +77,60 @@ struct vfsmount *alloc_vfsmnt(const char return mnt; } +/* + * Most r/o checks on a fs are for operations that take + * discrete amounts of time, like a write() or unlink(). + * We must keep track of when those operations start + * (for permission checks) and when they end, so that + * we can determine when writes are able to occur to + * a filesystem. + */ +/** + * mnt_want_write - get write access to a mount + * @mnt: the mount on which to take a write + * + * This tells the low-level filesystem that a write is + * about to be performed to it, and makes sure that + * writes are allowed before returning success. When + * the write operation is finished, mnt_drop_write() + * must be called. This is effectively a refcount. + */ +int mnt_want_write(struct vfsmount *mnt) +{ + if (__mnt_is_readonly(mnt)) + return -EROFS; + return 0; +} +EXPORT_SYMBOL_GPL(mnt_want_write); + +/** + * mnt_drop_write - give up write access to a mount + * @mnt: the mount on which to give up write access + * + * Tells the low-level filesystem that we are done + * performing writes to it. Must be matched with + * mnt_want_write() call above. + */ +void mnt_drop_write(struct vfsmount *mnt) +{ +} +EXPORT_SYMBOL_GPL(mnt_drop_write); + +/* + * __mnt_is_readonly: check whether a mount is read-only + * @mnt: the mount to check for its write status + * + * This shouldn't be used directly ouside of the VFS. + * It does not guarantee that the filesystem will stay + * r/w, just that it is right *now*. This can not and + * should not be used in place of IS_RDONLY(inode). + */ +int __mnt_is_readonly(struct vfsmount *mnt) +{ + return (mnt->mnt_sb->s_flags & MS_RDONLY); +} +EXPORT_SYMBOL_GPL(__mnt_is_readonly); + int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb) { mnt->mnt_sb = sb; diff -puN include/linux/mount.h~r-o-bind-mounts-stub-functions include/linux/mount.h --- linux-2.6.git/include/linux/mount.h~r-o-bind-mounts-stub-functions 2007-11-01 14:46:08.000000000 -0700 +++ linux-2.6.git-dave/include/linux/mount.h 2007-11-01 14:46:08.000000000 -0700 @@ -70,9 +70,12 @@ static inline struct vfsmount *mntget(st return mnt; } +extern int mnt_want_write(struct vfsmount *mnt); +extern void mnt_drop_write(struct vfsmount *mnt); extern void mntput_no_expire(struct vfsmount *mnt); extern void mnt_pin(struct vfsmount *mnt); extern void mnt_unpin(struct vfsmount *mnt); +extern int __mnt_is_readonly(struct vfsmount *mnt); static inline void mntput(struct vfsmount *mnt) { _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/