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Date: Fri, 08 Feb 2008 14:27:27 -0800
From: Dave Hansen <haveblue@...ibm.com>
To: linux-kernel@...r.kernel.org
Cc: hch@....de, viro@...IV.linux.org.uk, viro@....linux.org.uk,
miklos@...redi.hu, Dave Hansen <haveblue@...ibm.com>
Subject: [RFC][PATCH 29/30] r/o bind mounts: honor mount writer counts at remount
Originally from: Herbert Poetzl <herbert@...hfloor.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@...ibm.com>
Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Andrew Morton <akpm@...ux-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 */
_
--
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