[v3,2/3] btrfs: Add unprivileged ioctl which returns subvolume's ROOT_REF
diff mbox

Message ID b1b01fcb-f1a4-5e3e-64cf-0bb376f3c0a4@jp.fujitsu.com
State New
Headers show

Commit Message

Misono Tomohiro March 19, 2018, 7:27 a.m. UTC
Add unprivileged ioctl BTRFS_IOC_GET_SUBVOL_ROOTREF which
returns ROOT_REF information of the subvolume containing this inode.
The min id of root ref's subvolume to be searched is specified by
min_id in struct btrfs_ioctl_get_subvol_rootref_args.

If there are more root refs than BTRFS_MAX_ROOTREF_BUFFER_NUM,
this ioctl sets min_id to the last searched root ref's subvolid + 1
and return -EOVERFLOW. Therefore the caller can just call this ioctl
again without changing the argument to continue search.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/ioctl.c           | 91 ++++++++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h | 16 ++++++++
 2 files changed, 107 insertions(+)

Patch
diff mbox

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index be2abe7a5bba..5b97a735790e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2425,6 +2425,95 @@  static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
 	return ret;
 }
 
+/* Returns ROOT_REF information of the subvolume contining this inode. */
+static noinline 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 *l;
+	int slot;
+
+	struct inode *inode;
+	int i, nritems;
+	int ret;
+	u64 objectid;
+	u8 found;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	rootrefs = memdup_user(argp, sizeof(*rootrefs));
+	if (!rootrefs) {
+		btrfs_free_path(path);
+		return -ENOMEM;
+	}
+
+	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_id;
+	found = 0;
+	while (1) {
+		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		if (ret < 0)
+			goto out;
+
+		l = path->nodes[0];
+		slot = path->slots[0];
+		nritems = btrfs_header_nritems(l);
+		if (nritems - slot == 0) {
+			ret = 0;
+			goto out;
+		}
+
+		for (i = slot; i < nritems; i++) {
+			btrfs_item_key_to_cpu(l, &key, i);
+			if (key.objectid != objectid ||
+					key.type != BTRFS_ROOT_REF_KEY) {
+				ret = 0;
+				goto out;
+			}
+
+			if (found == BTRFS_MAX_ROOTREF_BUFFER_NUM) {
+				/* update min_id for next search */
+				rootrefs->min_id = key.offset;
+				ret = -EOVERFLOW;
+				goto out;
+			}
+
+			rref = btrfs_item_ptr(l, i, struct btrfs_root_ref);
+			rootrefs->rootref[found].subvolid = key.offset;
+			rootrefs->rootref[found].dirid =
+					  btrfs_root_ref_dirid(l, rref);
+			found++;
+		}
+
+		btrfs_release_path(path);
+		key.offset++;
+	}
+
+out:
+	if (!ret || ret == -EOVERFLOW) {
+		rootrefs->num_items = found;
+		if (copy_to_user(argp, rootrefs, sizeof(*rootrefs)))
+			ret = -EFAULT;
+	}
+
+	btrfs_free_path(path);
+	kfree(rootrefs);
+
+	return ret;
+}
+
 static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 					     void __user *arg)
 {
@@ -5781,6 +5870,8 @@  long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_set_features(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 ed053852c71f..82c88d52d6e6 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -774,6 +774,20 @@  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, min id of rootref's subvolid to be searched */
+		__u64 min_id;
+		/* out */
+		struct {
+			__u64 subvolid;
+			__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,
@@ -894,5 +908,7 @@  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 */