Commit 2e4b7fcd authored by Dave Hansen's avatar Dave Hansen Committed by Al Viro
Browse files

[PATCH] r/o bind mounts: honor mount writer counts at remount 



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

Acked-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarChristoph Hellwig <hch@infradead.org>
Signed-off-by: default avatarDave Hansen <haveblue@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 3d733633

fs/namespace.c

+43 −7
Original line number Diff line number Diff line
@@ -105,7 +105,11 @@ struct vfsmount *alloc_vfsmnt(const char *name) 
 */

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);
@@ -305,7 +309,7 @@ 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;
@@ -318,15 +322,25 @@ int mnt_make_readonly(struct vfsmount *mnt) 
		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;
@@ -693,7 +707,7 @@ static int show_vfsmnt(struct seq_file *m, void *v) 
		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);
@@ -1295,6 +1309,23 @@ 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
@@ -1317,6 +1348,9 @@ static noinline int do_remount(struct nameidata *nd, int flags, int mnt_flags, 
		return -EINVAL;



	down_write(&sb->s_umount);

	if (flags & MS_BIND)

		err = change_mount_flags(nd->path.mnt, flags);

	else

		err = do_remount_sb(sb, flags, data, 0);

	if (!err)

		nd->path.mnt->mnt_flags = mnt_flags;
@@ -1701,6 +1735,8 @@ long do_mount(char *dev_name, char *dir_name, char *type_page, 
		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);

include/linux/mount.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */

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