lkml.org 
[lkml]   [2006]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH 20/20] honor r/w changes at do_remount() time
From
Date

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.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---
lxc-dave/fs/namespace.c | 27 +++++++++++++++++++++++++--
lxc-dave/fs/open.c | 2 +-
lxc-dave/include/linux/mount.h | 19 +++++++++++++++++++
3 files changed, 45 insertions(+), 3 deletions(-)
diff -puN fs/namespace.c~C-D8-actually-add-flags fs/namespace.c
--- lxc/fs/namespace.c~C-D8-actually-add-flags 2006-06-27 10:40:36.000000000 -0700
+++ lxc-dave/fs/namespace.c 2006-06-27 10:40:36.000000000 -0700
@@ -387,7 +387,10 @@ static int show_vfsmnt(struct seq_file *
seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
seq_putc(m, ' ');
mangle(m, mnt->mnt_sb->s_type->name);
- seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
+ if ((mnt->mnt_sb->s_flags & MS_RDONLY) || __mnt_is_readonly(mnt))
+ seq_puts(m, " ro");
+ else
+ seq_puts(m, " 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);
@@ -956,6 +959,23 @@ 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_make_writable(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
@@ -977,7 +997,10 @@ 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);
diff -puN fs/open.c~C-D8-actually-add-flags fs/open.c
--- lxc/fs/open.c~C-D8-actually-add-flags 2006-06-27 10:40:36.000000000 -0700
+++ lxc-dave/fs/open.c 2006-06-27 10:40:36.000000000 -0700
@@ -546,7 +546,7 @@ asmlinkage long sys_faccessat(int dfd, c
special_file(nd.dentry->d_inode->i_mode))
goto out_path_release;

- if(IS_RDONLY(nd.dentry->d_inode))
+ if(mnt_is_readonly(nd.mnt) || IS_RDONLY(nd.dentry->d_inode))
res = -EROFS;

out_path_release:
diff -puN include/linux/mount.h~C-D8-actually-add-flags include/linux/mount.h
--- lxc/include/linux/mount.h~C-D8-actually-add-flags 2006-06-27 10:40:36.000000000 -0700
+++ lxc-dave/include/linux/mount.h 2006-06-27 10:40:36.000000000 -0700
@@ -98,6 +98,25 @@ static inline int __mnt_is_readonly(stru
return (atomic_read(&mnt->mnt_writers) == 0);
}

+/*
+ * This needs to get a consistent look at mnt_writers.
+ * Without the lock, it can race against mnt_make_readonly()
+ * and mistake a temporarily decremented mnt_writers
+ * for a real read-only mount.
+ *
+ * Note: this is never suitable if you need to perform any
+ * write *operations* on the mount, only as a snapshot.
+ */
+static inline int mnt_is_readonly(struct vfsmount *mnt)
+{
+ int ret;
+
+ down_read(&mnt->mnt_sb->s_umount);
+ ret = __mnt_is_readonly(mnt);
+ up_read(&mnt->mnt_sb->s_umount);
+ return ret;
+}
+
static inline int mnt_want_write(struct vfsmount *mnt)
{
int ret = 0;
_
-
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/
\
 
 \ /
  Last update: 2006-06-28 00:18    [from the cache]
©2003-2011 Jasper Spaans. Advertise on this site