btrfs: Add unprivileged ioctl which returns subvolume information

Add new unprivileged ioctl BTRFS_IOC_GET_SUBVOL_INFO which returns
the information of subvolume containing this inode.
(i.e. returns the information in ROOT_ITEM and ROOT_BACKREF.)

Reviewed-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Tested-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
[ minor style fixes, update struct comments ]
Signed-off-by: David Sterba <dsterba@suse.com>

2 files changed, 183 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 4db2446c7015..42ed752288e6 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2383,6 +2383,125 @@ out:
         return ret;
 }
 
+/* Get the subvolume information in BTRFS_ROOT_ITEM and BTRFS_ROOT_BACKREF */
+static int btrfs_ioctl_get_subvol_info(struct file *file, void __user *argp)
+{
+        struct btrfs_ioctl_get_subvol_info_args *subvol_info;
+        struct btrfs_fs_info *fs_info;
+        struct btrfs_root *root;
+        struct btrfs_path *path;
+        struct btrfs_key key;
+        struct btrfs_root_item *root_item;
+        struct btrfs_root_ref *rref;
+        struct extent_buffer *leaf;
+        unsigned long item_off;
+        unsigned long item_len;
+        struct inode *inode;
+        int slot;
+        int ret = 0;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+
+        subvol_info = kzalloc(sizeof(*subvol_info), GFP_KERNEL);
+        if (!subvol_info) {
+                btrfs_free_path(path);
+                return -ENOMEM;
+        }
+
+        inode = file_inode(file);
+        fs_info = BTRFS_I(inode)->root->fs_info;
+
+        /* Get root_item of inode's subvolume */
+        key.objectid = BTRFS_I(inode)->root->root_key.objectid;
+        key.type = BTRFS_ROOT_ITEM_KEY;
+        key.offset = (u64)-1;
+        root = btrfs_read_fs_root_no_name(fs_info, &key);
+        if (IS_ERR(root)) {
+                ret = PTR_ERR(root);
+                goto out;
+        }
+        root_item = &root->root_item;
+
+        subvol_info->treeid = key.objectid;
+
+        subvol_info->generation = btrfs_root_generation(root_item);
+        subvol_info->flags = btrfs_root_flags(root_item);
+
+        memcpy(subvol_info->uuid, root_item->uuid, BTRFS_UUID_SIZE);
+        memcpy(subvol_info->parent_uuid, root_item->parent_uuid,
+                                                    BTRFS_UUID_SIZE);
+        memcpy(subvol_info->received_uuid, root_item->received_uuid,
+                                                    BTRFS_UUID_SIZE);
+
+        subvol_info->ctransid = btrfs_root_ctransid(root_item);
+        subvol_info->ctime.sec = btrfs_stack_timespec_sec(&root_item->ctime);
+        subvol_info->ctime.nsec = btrfs_stack_timespec_nsec(&root_item->ctime);
+
+        subvol_info->otransid = btrfs_root_otransid(root_item);
+        subvol_info->otime.sec = btrfs_stack_timespec_sec(&root_item->otime);
+        subvol_info->otime.nsec = btrfs_stack_timespec_nsec(&root_item->otime);
+
+        subvol_info->stransid = btrfs_root_stransid(root_item);
+        subvol_info->stime.sec = btrfs_stack_timespec_sec(&root_item->stime);
+        subvol_info->stime.nsec = btrfs_stack_timespec_nsec(&root_item->stime);
+
+        subvol_info->rtransid = btrfs_root_rtransid(root_item);
+        subvol_info->rtime.sec = btrfs_stack_timespec_sec(&root_item->rtime);
+        subvol_info->rtime.nsec = btrfs_stack_timespec_nsec(&root_item->rtime);
+
+        if (key.objectid != BTRFS_FS_TREE_OBJECTID) {
+                /* Search root tree for ROOT_BACKREF of this subvolume */
+                root = fs_info->tree_root;
+
+                key.type = BTRFS_ROOT_BACKREF_KEY;
+                key.offset = 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;
+                        }
+                }
+
+                leaf = path->nodes[0];
+                slot = path->slots[0];
+                btrfs_item_key_to_cpu(leaf, &key, slot);
+                if (key.objectid == subvol_info->treeid &&
+                    key.type == BTRFS_ROOT_BACKREF_KEY) {
+                        subvol_info->parent_id = key.offset;
+
+                        rref = btrfs_item_ptr(leaf, slot, struct btrfs_root_ref);
+                        subvol_info->dirid = btrfs_root_ref_dirid(leaf, rref);
+
+                        item_off = btrfs_item_ptr_offset(leaf, slot)
+                                        + sizeof(struct btrfs_root_ref);
+                        item_len = btrfs_item_size_nr(leaf, slot)
+                                        - sizeof(struct btrfs_root_ref);
+                        read_extent_buffer(leaf, subvol_info->name,
+                                           item_off, item_len);
+                } else {
+                        ret = -ENOENT;
+                        goto out;
+                }
+        }
+
+        if (copy_to_user(argp, subvol_info, sizeof(*subvol_info)))
+                ret = -EFAULT;
+
+out:
+        btrfs_free_path(path);
+        kzfree(subvol_info);
+        return ret;
+}
+
 static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                                              void __user *arg)
 {
@@ -5545,6 +5664,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_fsgetxattr(file, argp);
         case FS_IOC_FSSETXATTR:
                 return btrfs_ioctl_fssetxattr(file, argp);
+        case BTRFS_IOC_GET_SUBVOL_INFO:
+                return btrfs_ioctl_get_subvol_info(file, argp);
         }
 
         return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index c8d99b9ca550..f8f20d72b852 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -725,6 +725,66 @@ struct btrfs_ioctl_send_args {
         __u64 reserved[4];              /* in */
 };
 
+/*
+ * Information about a fs tree root.
+ *
+ * All items are filled by the ioctl
+ */
+struct btrfs_ioctl_get_subvol_info_args {
+        /* Id of this subvolume */
+        __u64 treeid;
+
+        /* Name of this subvolume, used to get the real name at mount point */
+        char name[BTRFS_VOL_NAME_MAX + 1];
+
+        /*
+         * Id of the subvolume which contains this subvolume.
+         * Zero for top-level subvolume or a deleted subvolume.
+         */
+        __u64 parent_id;
+
+        /*
+         * Inode number of the directory which contains this subvolume.
+         * Zero for top-level subvolume or a deleted subvolume
+         */
+        __u64 dirid;
+
+        /* Latest transaction id of this subvolume */
+        __u64 generation;
+
+        /* Flags of this subvolume */
+        __u64 flags;
+
+        /* UUID of this subvolume */
+        __u8 uuid[BTRFS_UUID_SIZE];
+
+        /*
+         * UUID of the subvolume of which this subvolume is a snapshot.
+         * All zero for a non-snapshot subvolume.
+         */
+        __u8 parent_uuid[BTRFS_UUID_SIZE];
+
+        /*
+         * UUID of the subvolume from which this subvolume was received.
+         * All zero for non-received subvolume.
+         */
+        __u8 received_uuid[BTRFS_UUID_SIZE];
+
+        /* Transaction id indicating when change/create/send/receive happened */
+        __u64 ctransid;
+        __u64 otransid;
+        __u64 stransid;
+        __u64 rtransid;
+        /* Time corresponding to c/o/s/rtransid */
+        struct btrfs_ioctl_timespec ctime;
+        struct btrfs_ioctl_timespec otime;
+        struct btrfs_ioctl_timespec stime;
+        struct btrfs_ioctl_timespec rtime;
+
+        /* Must be zero */
+        __u64 reserved[8];
+};
+
 /* Error codes as returned by the kernel */
 enum btrfs_err_code {
         BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET = 1,
@@ -843,5 +903,7 @@ enum btrfs_err_code {
                                    struct btrfs_ioctl_vol_args_v2)
 #define BTRFS_IOC_LOGICAL_INO_V2 _IOWR(BTRFS_IOCTL_MAGIC, 59, \
                                         struct btrfs_ioctl_logical_ino_args)
+#define BTRFS_IOC_GET_SUBVOL_INFO _IOR(BTRFS_IOCTL_MAGIC, 60, \
+                                struct btrfs_ioctl_get_subvol_info_args)
 
 #endif /* _UAPI_LINUX_BTRFS_H */