The attached patch extends the get_sb() filesystem operation to take an extra
argument that permits the default root dentry choice (sb->s_root) to be
overridden by the filesystem that owns the superblock.
If the dentry pointer pointed to by that argument is left unchanged, then
do_kern_mount() will use sb->s_root as the root of the mount. If the filesystem
sets the pointer to a dentry of its choice, then that will be used as the root
for that particular mount.
This patch permits a superblock to be implicitly shared amongst several mount
points, such as can be done with NFS to avoid potential inode aliasing (see
patch 5/5).
Signed-Off-By: David Howells <dhowells@xxxxxxxxxx>
---
warthog>diffstat -p1 getsb-2616rc4.diff
Documentation/filesystems/porting | 2 +-
fs/super.c | 10 +++++++---
include/linux/fs.h | 2 +-
3 files changed, 9 insertions(+), 5 deletions(-)
diff -uNrp linux-2.6.16-rc4/Documentation/filesystems/porting linux-2.6.16-rc4-getsb/Documentation/filesystems/porting
--- linux-2.6.16-rc4/Documentation/filesystems/porting 2004-06-18 13:42:30.000000000 +0100
+++ linux-2.6.16-rc4-getsb/Documentation/filesystems/porting 2006-02-22 17:11:59.000000000 +0000
@@ -51,7 +51,7 @@ success and negative number in case of e
informative error value to report). Call it foo_fill_super(). Now declare
struct super_block foo_get_sb(struct file_system_type *fs_type,
- int flags, const char *dev_name, void *data)
+ int flags, const char *dev_name, void *data, struct dentry **_root)
{
return get_sb_bdev(fs_type, flags, dev_name, data, ext2_fill_super);
}
diff -uNrp linux-2.6.16-rc4/include/linux/fs.h linux-2.6.16-rc4-getsb/include/linux/fs.h
--- linux-2.6.16-rc4/include/linux/fs.h 2006-02-22 17:00:41.000000000 +0000
+++ linux-2.6.16-rc4-getsb/include/linux/fs.h 2006-02-22 17:08:45.000000000 +0000
@@ -1240,7 +1240,7 @@ struct file_system_type {
const char *name;
int fs_flags;
struct super_block *(*get_sb) (struct file_system_type *, int,
- const char *, void *);
+ const char *, void *, struct dentry **);
void (*kill_sb) (struct super_block *);
struct module *owner;
struct file_system_type * next;
diff -uNrp linux-2.6.16-rc4/fs/super.c linux-2.6.16-rc4-getsb/fs/super.c
--- linux-2.6.16-rc4/fs/super.c 2006-02-22 17:00:38.000000000 +0000
+++ linux-2.6.16-rc4-getsb/fs/super.c 2006-02-22 17:08:45.000000000 +0000
@@ -792,6 +792,7 @@ do_kern_mount(const char *fstype, int fl
struct file_system_type *type = get_fs_type(fstype);
struct super_block *sb = ERR_PTR(-ENOMEM);
struct vfsmount *mnt;
+ struct dentry *root;
int error;
char *secdata = NULL;
@@ -816,15 +817,18 @@ do_kern_mount(const char *fstype, int fl
}
}
- sb = type->get_sb(type, flags, name, data);
+ root = NULL;
+ sb = type->get_sb(type, flags, name, data, &root);
if (IS_ERR(sb))
goto out_free_secdata;
+ if (!root)
+ root = dget(sb->s_root);
error = security_sb_kern_mount(sb, secdata);
if (error)
goto out_sb;
mnt->mnt_sb = sb;
- mnt->mnt_root = dget(sb->s_root);
- mnt->mnt_mountpoint = sb->s_root;
+ mnt->mnt_root = root;
+ mnt->mnt_mountpoint = root;
mnt->mnt_parent = mnt;
up_write(&sb->s_umount);
free_secdata(secdata);
