UBUNTU: SAUCE: overlayfs -- vfs: add i_op->open()

Add a new inode operation i_op->open().  This is for stacked
filesystems that want to return a struct file from a different
filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andy Whitcroft <apw@canonical.com>

diff --git a/fs/open.c b/fs/open.c
index 4e798b1..caebfd7 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -647,8 +647,7 @@ static inline int __get_file_write_access(struct inode *inode,
        return error;
 }
 
-static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
-                                       struct file *f,
+static struct file *__dentry_open(struct path *path, struct file *f,
                                        int (*open)(struct inode *, struct file *),
                                        const struct cred *cred)
 {
@@ -656,15 +655,16 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
        struct inode *inode;
        int error;
 
+       path_get(path);
        f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
                                FMODE_PREAD | FMODE_PWRITE;
 
        if (unlikely(f->f_flags & O_PATH))
                f->f_mode = FMODE_PATH;
 
-       inode = dentry->d_inode;
+       inode = path->dentry->d_inode;
        if (f->f_mode & FMODE_WRITE) {
-               error = __get_file_write_access(inode, mnt);
+               error = __get_file_write_access(inode, path->mnt);
                if (error)
                        goto cleanup_file;
                if (!special_file(inode->i_mode))
@@ -672,8 +672,7 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
        }
 
        f->f_mapping = inode->i_mapping;
-       f->f_path.dentry = dentry;
-       f->f_path.mnt = mnt;
+       f->f_path = *path;
        f->f_pos = 0;
        file_sb_list_add(f, inode->i_sb);
 
@@ -730,7 +729,7 @@ cleanup_all:
                         * here, so just reset the state.
                         */
                        file_reset_write(f);
-                       mnt_drop_write(mnt);
+                       mnt_drop_write(path->mnt);
                }
        }
        file_sb_list_del(f);
@@ -738,8 +737,7 @@ cleanup_all:
        f->f_path.mnt = NULL;
 cleanup_file:
        put_filp(f);
-       dput(dentry);
-       mntput(mnt);
+       path_put(path);
        return ERR_PTR(error);
 }
 
@@ -765,14 +763,14 @@ cleanup_file:
 struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
                int (*open)(struct inode *, struct file *))
 {
+       struct path path = { .dentry = dentry, .mnt = nd->path.mnt };
        const struct cred *cred = current_cred();
 
        if (IS_ERR(nd->intent.open.file))
                goto out;
        if (IS_ERR(dentry))
                goto out_err;
-       nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->path.mnt),
-                                            nd->intent.open.file,
+       nd->intent.open.file = __dentry_open(&path, nd->intent.open.file,
                                             open, cred);
 out:
        return nd->intent.open.file;
@@ -801,10 +799,17 @@ struct file *nameidata_to_filp(struct nameidata *nd)
 
        /* Has the filesystem initialised the file for us? */
        if (filp->f_path.dentry == NULL) {
-               path_get(&nd->path);
-               filp = __dentry_open(nd->path.dentry, nd->path.mnt, filp,
-                                    NULL, cred);
+               struct inode *inode = nd->path.dentry->d_inode;
+
+               if (inode->i_op->open) {
+                       int flags = filp->f_flags;
+                       put_filp(filp);
+                       filp = inode->i_op->open(nd->path.dentry, flags, cred);
+               } else {
+                       filp = __dentry_open(&nd->path, filp, NULL, cred);
+               }
        }
+
        return filp;
 }
 
@@ -815,26 +820,45 @@ struct file *nameidata_to_filp(struct nameidata *nd)
 struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
                         const struct cred *cred)
 {
-       int error;
-       struct file *f;
-
-       validate_creds(cred);
+       struct path path = { .dentry = dentry, .mnt = mnt };
+       struct file *ret;
 
        /* We must always pass in a valid mount pointer. */
        BUG_ON(!mnt);
 
-       error = -ENFILE;
+       ret = vfs_open(&path, flags, cred);
+       path_put(&path);
+
+       return ret;
+}
+EXPORT_SYMBOL(dentry_open);
+
+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @flags: open flags
+ * @cred: credentials to use
+ *
+ * Open the file.  If successful, the returned file will have acquired
+ * an additional reference for path.
+ */
+struct file *vfs_open(struct path *path, int flags, const struct cred *cred)
+{
+       struct file *f;
+       struct inode *inode = path->dentry->d_inode;
+
+       validate_creds(cred);
+
+       if (inode->i_op->open)
+               return inode->i_op->open(path->dentry, flags, cred);
        f = get_empty_filp();
-       if (f == NULL) {
-               dput(dentry);
-               mntput(mnt);
-               return ERR_PTR(error);
-       }
+       if (f == NULL)
+               return ERR_PTR(-ENFILE);
 
        f->f_flags = flags;
-       return __dentry_open(dentry, mnt, f, NULL, cred);
+       return __dentry_open(path, f, NULL, cred);
 }
-EXPORT_SYMBOL(dentry_open);
+EXPORT_SYMBOL(vfs_open);
 
 static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 {

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 10b2288..737ce9c 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1639,6 +1639,7 @@ struct inode_operations {
        void (*truncate_range)(struct inode *, loff_t, loff_t);
        int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
                      u64 len);
+       struct file *(*open)(struct dentry *, int flags, const struct cred *);
 } ____cacheline_aligned;
 
 struct seq_file;
@@ -2059,6 +2060,7 @@ extern long do_sys_open(int dfd, const char __user *filename, int flags,
 extern struct file *filp_open(const char *, int, int);
 extern struct file *file_open_root(struct dentry *, struct vfsmount *,
                                   const char *, int);
+extern struct file *vfs_open(struct path *, int flags, const struct cred *);
 extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
                                 const struct cred *);
 extern int filp_close(struct file *, fl_owner_t id);