[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: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Dave Hansen 2008-02-15 14:38:00 -08:00 committed by Al Viro
parent 3d733633a6
commit 2e4b7fcd92
2 changed files with 44 additions and 7 deletions

View file

@ -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
@ -1317,7 +1348,10 @@ static noinline int do_remount(struct nameidata *nd, int flags, int mnt_flags,
return -EINVAL;
down_write(&sb->s_umount);
err = do_remount_sb(sb, flags, data, 0);
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;
up_write(&sb->s_umount);
@ -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);

View file

@ -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 */