2 files changed, 117 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 42ed752288e6..be9b3f39183c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2502,6 +2502,103 @@ out:
         return ret;
 }
 
+/*
+ * Return ROOT_REF information of the subvolume containing this inode
+ * except the subvolume name.
+ */
+static int btrfs_ioctl_get_subvol_rootref(struct file *file, void __user *argp)
+{
+        struct btrfs_ioctl_get_subvol_rootref_args *rootrefs;
+        struct btrfs_root_ref *rref;
+        struct btrfs_root *root;
+        struct btrfs_path *path;
+        struct btrfs_key key;
+        struct extent_buffer *leaf;
+        struct inode *inode;
+        u64 objectid;
+        int slot;
+        int ret;
+        u8 found;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+
+        rootrefs = memdup_user(argp, sizeof(*rootrefs));
+        if (IS_ERR(rootrefs)) {
+                btrfs_free_path(path);
+                return PTR_ERR(rootrefs);
+        }
+
+        inode = file_inode(file);
+        root = BTRFS_I(inode)->root->fs_info->tree_root;
+        objectid = BTRFS_I(inode)->root->root_key.objectid;
+
+        key.objectid = objectid;
+        key.type = BTRFS_ROOT_REF_KEY;
+        key.offset = rootrefs->min_treeid;
+        found = 0;
+
+        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+        if (ret < 0) {
+                goto out;
+        } else if (path->slots[0] >=
+                   btrfs_header_nritems(path->nodes[0])) {
+                ret = btrfs_next_leaf(root, path);
+                if (ret < 0) {
+                        goto out;
+                } else if (ret > 0) {
+                        ret = -EUCLEAN;
+                        goto out;
+                }
+        }
+        while (1) {
+                leaf = path->nodes[0];
+                slot = path->slots[0];
+
+                btrfs_item_key_to_cpu(leaf, &key, slot);
+                if (key.objectid != objectid || key.type != BTRFS_ROOT_REF_KEY) {
+                        ret = 0;
+                        goto out;
+                }
+
+                if (found == BTRFS_MAX_ROOTREF_BUFFER_NUM) {
+                        ret = -EOVERFLOW;
+                        goto out;
+                }
+
+                rref = btrfs_item_ptr(leaf, slot, struct btrfs_root_ref);
+                rootrefs->rootref[found].treeid = key.offset;
+                rootrefs->rootref[found].dirid =
+                                  btrfs_root_ref_dirid(leaf, rref);
+                found++;
+
+                ret = btrfs_next_item(root, path);
+                if (ret < 0) {
+                        goto out;
+                } else if (ret > 0) {
+                        ret = -EUCLEAN;
+                        goto out;
+                }
+        }
+
+out:
+        if (!ret || ret == -EOVERFLOW) {
+                rootrefs->num_items = found;
+                /* update min_treeid for next search */
+                if (found)
+                        rootrefs->min_treeid =
+                                rootrefs->rootref[found - 1].treeid + 1;
+                if (copy_to_user(argp, rootrefs, sizeof(*rootrefs)))
+                        ret = -EFAULT;
+        }
+
+        kfree(rootrefs);
+        btrfs_free_path(path);
+
+        return ret;
+}
+
 static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                                              void __user *arg)
 {
@@ -5666,6 +5763,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_fssetxattr(file, argp);
         case BTRFS_IOC_GET_SUBVOL_INFO:
                 return btrfs_ioctl_get_subvol_info(file, argp);
+        case BTRFS_IOC_GET_SUBVOL_ROOTREF:
+                return btrfs_ioctl_get_subvol_rootref(file, argp);
         }
 
         return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index f8f20d72b852..f90d10478235 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -785,6 +785,22 @@ struct btrfs_ioctl_get_subvol_info_args {
         __u64 reserved[8];
 };
 
+#define BTRFS_MAX_ROOTREF_BUFFER_NUM 255
+struct btrfs_ioctl_get_subvol_rootref_args {
+                /* in/out, minimum id of rootref's treeid to be searched */
+                __u64 min_treeid;
+
+                /* out */
+                struct {
+                        __u64 treeid;
+                        __u64 dirid;
+                } rootref[BTRFS_MAX_ROOTREF_BUFFER_NUM];
+
+                /* out, number of found items */
+                __u8 num_items;
+                __u8 align[7];
+};
+
 /* Error codes as returned by the kernel */
 enum btrfs_err_code {
         BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET = 1,
@@ -905,5 +921,7 @@ enum btrfs_err_code {
                                         struct btrfs_ioctl_logical_ino_args)
 #define BTRFS_IOC_GET_SUBVOL_INFO _IOR(BTRFS_IOCTL_MAGIC, 60, \
                                 struct btrfs_ioctl_get_subvol_info_args)
+#define BTRFS_IOC_GET_SUBVOL_ROOTREF _IOWR(BTRFS_IOCTL_MAGIC, 61, \
+                                struct btrfs_ioctl_get_subvol_rootref_args)
 
 #endif /* _UAPI_LINUX_BTRFS_H */