On Tue, Mar 8, 2016 at 10:47 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxxxxx>
>
> Regular files opened on overlayfs will result in the file being opened on
> the underlying filesystem, while f_path points to the overlayfs
> mount/dentry.
>
> This confuses filesystems which get the dentry from struct file and assume
> it's theirs.
>
> Add a new helper, file_dentry() [*], to get the filesystem's own dentry
> from the file. This simply compares file_inode(file->f_path.dentry) to
> file_inode(file) and if they are equal returns file->f_path.dentry (this is
> the common, non-overlayfs case).
>
> In the uncommon case (regular file on overlayfs) it will call into
> overlayfs's ->d_native_dentry() to get the underlying dentry matching
> file_inode(file).
>
> [*] If possible, it's better simply to use file_inode() instead.
>
> Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> Tested-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Reviewed-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/open.c | 11 +++++++++++
> fs/overlayfs/super.c | 16 ++++++++++++++++
> include/linux/dcache.h | 1 +
> include/linux/fs.h | 2 ++
> 4 files changed, 30 insertions(+)
>
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(c
> return f->f_inode;
> }
>
> +extern struct dentry *file_dentry(const struct file *file);
> +
> static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
> {
> return locks_lock_inode_wait(file_inode(filp), fl);
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char
> }
> EXPORT_SYMBOL(file_path);
>
> +struct dentry *file_dentry(const struct file *file)
> +{
> + struct dentry *dentry = file->f_path.dentry;
> +
> + if (likely(d_inode(dentry) == file_inode(file)))
> + return dentry;
> + else
> + return dentry->d_op->d_native_dentry(dentry, file_inode(file));
> +}
> +EXPORT_SYMBOL(file_dentry);
> +
> /**
> * vfs_open - open the file at the given path
> * @path: path to open
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(st
> return ret;
> }
>
> +static struct dentry *ovl_d_native_dentry(struct dentry *dentry,
> + struct inode *inode)
> +{
> + struct ovl_entry *oe = dentry->d_fsdata;
> + struct dentry *realentry = ovl_upperdentry_dereference(oe);
> +
> + if (realentry && inode == d_inode(realentry))
> + return realentry;
> + realentry = __ovl_dentry_lower(oe);
> + if (realentry && inode == d_inode(realentry))
> + return realentry;
> + BUG();
> +}
> +
> static const struct dentry_operations ovl_dentry_operations = {
> .d_release = ovl_dentry_release,
> .d_select_inode = ovl_d_select_inode,
> + .d_native_dentry = ovl_d_native_dentry,
> };
>
> static const struct dentry_operations ovl_reval_dentry_operations = {
> .d_release = ovl_dentry_release,
> .d_select_inode = ovl_d_select_inode,
> + .d_native_dentry = ovl_d_native_dentry,
> .d_revalidate = ovl_dentry_revalidate,
> .d_weak_revalidate = ovl_dentry_weak_revalidate,
> };
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -161,6 +161,7 @@ struct dentry_operations {
> struct vfsmount *(*d_automount)(struct path *);
> int (*d_manage)(struct dentry *, bool);
> struct inode *(*d_select_inode)(struct dentry *, unsigned);
> + struct dentry *(*d_native_dentry)(struct dentry *, struct inode *);
> } ____cacheline_aligned;
>
> /*
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