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    SubjectRe: [PATCH 1/4] vfs: add file_dentry()
    On Thu, Mar 17, 2016 at 10:02:00AM +0100, Miklos Szeredi wrote:
    > From: Miklos Szeredi <mszeredi@redhat.com>
    >
    > This series fixes bugs in nfs and ext4 due to 4bacc9c9234c ("overlayfs: Make
    > f_path always point to the overlay and f_inode to the underlay").
    >
    > 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.
    >
    > Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
    > Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
    > Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com>
    > Cc: <stable@vger.kernel.org> # v4.2
    > Cc: David Howells <dhowells@redhat.com>
    > Cc: Al Viro <viro@zeniv.linux.org.uk>
    > Cc: Theodore Ts'o <tytso@mit.edu>
    > Cc: Daniel Axtens <dja@axtens.net>
    > ---
    > fs/open.c | 11 +++++++++++
    > fs/overlayfs/super.c | 16 ++++++++++++++++
    > include/linux/dcache.h | 1 +
    > include/linux/fs.h | 2 ++
    > 4 files changed, 30 insertions(+)

    I have this patch in the ext4.git tree, but I'd like to get an
    Acked-by from Al before I send a pull request to Linus.

    Al? Any objections to my sending in this change via the ext4 tree?

    - Ted

    >
    > diff --git a/fs/open.c b/fs/open.c
    > index 55bdc75e2172..6326c11eda78 100644
    > --- a/fs/open.c
    > +++ b/fs/open.c
    > @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char *buf, int buflen)
    > }
    > 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
    > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
    > index 619ad4b016d2..5142aa2034c4 100644
    > --- a/fs/overlayfs/super.c
    > +++ b/fs/overlayfs/super.c
    > @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
    > 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,
    > };
    > diff --git a/include/linux/dcache.h b/include/linux/dcache.h
    > index c4b5f4b3f8f8..99ecb6de636c 100644
    > --- 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;
    >
    > /*
    > diff --git a/include/linux/fs.h b/include/linux/fs.h
    > index ae681002100a..1091d9f43271 100644
    > --- a/include/linux/fs.h
    > +++ b/include/linux/fs.h
    > @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(const struct file *f)
    > 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);
    > --
    > 2.1.4
    >

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