LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Dave Hansen <haveblue@us.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: hch@lst.de, viro@ZenIV.linux.org.uk, viro@ftp.linux.org.uk,
	miklos@szeredi.hu, Dave Hansen <haveblue@us.ibm.com>
Subject: [RFC][PATCH 29/30] r/o bind mounts: honor mount writer counts at remount
Date: Fri, 08 Feb 2008 14:27:27 -0800	[thread overview]
Message-ID: <20080208222727.0F5093DA@kernel> (raw)
In-Reply-To: <20080208222641.6024A7CC@kernel>


Originally from: Herbert Poetzl <herbert@13thfloor.at>

This is the core of the read-only bind mount patch set.

Note that this does _not_ add a "ro" option directly to the bind mount
operation.  If you require such a mount, you must first do the bind, then
follow it up with a 'mount -o remount,ro' operation:

If you wish to have a r/o bind mount of /foo on bar:

	mount --bind /foo /bar
	mount -o remount,ro /bar

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 linux-2.6.git-dave/fs/namespace.c        |   50 ++++++++++++++++++++++++++-----
 linux-2.6.git-dave/include/linux/mount.h |    1 
 2 files changed, 44 insertions(+), 7 deletions(-)

diff -puN fs/namespace.c~r-o-bind-mounts-honor-r-w-changes-at-do_remount-time fs/namespace.c
--- linux-2.6.git/fs/namespace.c~r-o-bind-mounts-honor-r-w-changes-at-do_remount-time	2008-02-08 13:05:01.000000000 -0800
+++ linux-2.6.git-dave/fs/namespace.c	2008-02-08 13:05:01.000000000 -0800
@@ -105,7 +105,11 @@ struct vfsmount *alloc_vfsmnt(const char
  */
 int __mnt_is_readonly(struct vfsmount *mnt)
 {
-	return (mnt->mnt_sb->s_flags & MS_RDONLY);
+	if (mnt->mnt_flags & MNT_READONLY)
+		return 1;
+	if (mnt->mnt_sb->s_flags & MS_RDONLY)
+		return 1;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 
@@ -299,7 +303,7 @@ void mnt_drop_write(struct vfsmount *mnt
 }
 EXPORT_SYMBOL_GPL(mnt_drop_write);
 
-int mnt_make_readonly(struct vfsmount *mnt)
+static int mnt_make_readonly(struct vfsmount *mnt)
 {
 	int ret = 0;
 
@@ -312,15 +316,25 @@ int mnt_make_readonly(struct vfsmount *m
 		goto out;
 	}
 	/*
-	 * actually set mount's r/o flag here to make
-	 * __mnt_is_readonly() true, which keeps anyone
-	 * from doing a successful mnt_want_write().
+	 * nobody can do a successful mnt_want_write() with all
+	 * of the counts in MNT_DENIED_WRITE and the locks held.
 	 */
+	spin_lock(&vfsmount_lock);
+	if (!ret)
+		mnt->mnt_flags |= MNT_READONLY;
+	spin_unlock(&vfsmount_lock);
 out:
 	unlock_mnt_writers();
 	return ret;
 }
 
+static void __mnt_unmake_readonly(struct vfsmount *mnt)
+{
+	spin_lock(&vfsmount_lock);
+	mnt->mnt_flags &= ~MNT_READONLY;
+	spin_unlock(&vfsmount_lock);
+}
+
 int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
 {
 	mnt->mnt_sb = sb;
@@ -643,7 +657,7 @@ static int show_vfsmnt(struct seq_file *
 		seq_putc(m, '.');
 		mangle(m, mnt->mnt_sb->s_subtype);
 	}
-	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
+	seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
 	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
 		if (mnt->mnt_sb->s_flags & fs_infop->flag)
 			seq_puts(m, fs_infop->str);
@@ -1231,6 +1245,23 @@ out:
 	return err;
 }
 
+static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
+{
+	int error = 0;
+	int readonly_request = 0;
+
+	if (ms_flags & MS_RDONLY)
+		readonly_request = 1;
+	if (readonly_request == __mnt_is_readonly(mnt))
+		return 0;
+
+	if (readonly_request)
+		error = mnt_make_readonly(mnt);
+	else
+		__mnt_unmake_readonly(mnt);
+	return error;
+}
+
 /*
  * change filesystem flags. dir should be a physical root of filesystem.
  * If you've mounted a non-root directory somewhere and want to do remount
@@ -1252,7 +1283,10 @@ static int do_remount(struct nameidata *
 		return -EINVAL;
 
 	down_write(&sb->s_umount);
-	err = do_remount_sb(sb, flags, data, 0);
+	if (flags & MS_BIND)
+		err = change_mount_flags(nd->mnt, flags);
+	else
+		err = do_remount_sb(sb, flags, data, 0);
 	if (!err)
 		nd->mnt->mnt_flags = mnt_flags;
 	up_write(&sb->s_umount);
@@ -1696,6 +1730,8 @@ long do_mount(char *dev_name, char *dir_
 		mnt_flags |= MNT_NODIRATIME;
 	if (flags & MS_RELATIME)
 		mnt_flags |= MNT_RELATIME;
+	if (flags & MS_RDONLY)
+		mnt_flags |= MNT_READONLY;
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
 		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);
diff -puN include/linux/mount.h~r-o-bind-mounts-honor-r-w-changes-at-do_remount-time include/linux/mount.h
--- linux-2.6.git/include/linux/mount.h~r-o-bind-mounts-honor-r-w-changes-at-do_remount-time	2008-02-08 13:05:01.000000000 -0800
+++ linux-2.6.git-dave/include/linux/mount.h	2008-02-08 13:05:01.000000000 -0800
@@ -29,6 +29,7 @@ struct mnt_namespace;
 #define MNT_NOATIME	0x08
 #define MNT_NODIRATIME	0x10
 #define MNT_RELATIME	0x20
+#define MNT_READONLY	0x40	/* does the user want this to be r/o? */
 
 #define MNT_SHRINKABLE	0x100
 #define MNT_IMBALANCED_WRITE_COUNT	0x200 /* just for debugging */
_

  parent reply	other threads:[~2008-02-08 22:41 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 22:26 [RFC][PATCH 00/30] Read-only bind mounts (-mm resend) Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 01/30] reiserfs: eliminate private use of struct file in xattr Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 02/30] hppfs pass vfsmount to dentry_open() Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 03/30] check for null vfsmount in dentry_open() Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 04/30] fix up new filp allocators Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 05/30] do namei_flags calculation inside open_namei() Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 06/30] make open_namei() return a filp Dave Hansen
2008-02-09  5:09   ` Christoph Hellwig
2008-02-08 22:26 ` [RFC][PATCH 07/30] r/o bind mounts: stub functions Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 08/30] r/o bind mounts: create helper to drop file write access Dave Hansen
2008-02-08 22:26 ` [RFC][PATCH 09/30] r/o bind mounts: drop write during emergency remount Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 10/30] r/o bind mounts: elevate write count for vfs_rmdir() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 11/30] r/o bind mounts: elevate write count for callers of vfs_mkdir() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 12/30] r/o bind mounts: elevate mnt_writers for unlink callers Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 13/30] r/o bind mounts: elevate write count for xattr_permission() callers Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 14/30] r/o bind mounts: elevate write count for ncp_ioctl() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 15/30] r/o bind mounts: write counts for time functions Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 16/30] r/o bind mounts: elevate write count for do_utimes() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 17/30] r/o bind mounts: write count for file_update_time() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 18/30] r/o bind mounts: write counts for link/symlink Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 19/30] r/o bind mounts: elevate write count for ioctls() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 20/30] r/o bind mounts: elevate write count for open()s Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 21/30] r/o bind mounts: get write access for vfs_rename() callers Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 22/30] r/o bind mounts: elevate write count for chmod/chown callers Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 23/30] r/o bind mounts: write counts for truncate() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 24/30] r/o bind mounts: elevate count for xfs timestamp updates Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 25/30] r/o bind mounts: make access() use new r/o helper Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 26/30] r/o bind mounts: check mnt instead of superblock directly Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 27/30] r/o bind mounts: get callers of vfs_mknod/create() Dave Hansen
2008-02-08 22:27 ` [RFC][PATCH 28/30] r/o bind mounts: track numbers of writers to mounts Dave Hansen
2008-02-08 22:27 ` Dave Hansen [this message]
2008-02-08 22:27 ` [RFC][PATCH 30/30] r/o bind mounts: debugging for missed calls Dave Hansen
2008-02-09  6:39 ` [RFC][PATCH 00/30] Read-only bind mounts (-mm resend) Christoph Hellwig
2008-02-09  7:57 ` Al Viro
2008-02-12  5:06 ` Christoph Hellwig

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20080208222727.0F5093DA@kernel \
    --to=haveblue@us.ibm.com \
    --cc=hch@lst.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=miklos@szeredi.hu \
    --cc=viro@ZenIV.linux.org.uk \
    --cc=viro@ftp.linux.org.uk \
    --subject='Re: [RFC][PATCH 29/30] r/o bind mounts: honor mount writer counts at remount' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).