blob: a831ce83756c83fd08e2176c0bc986240ab2c95b [file] [log] [blame]
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* This file is part of libmount from util-linux project.
*
* Copyright (C) 2016 David Sterba <dsterba@suse.cz>
* Copyright (C) 2016 Stanislav Brabec <sbrabec@suse.cz>
*
* libmount is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* Based on kernel ctree.h, rbtree.h and btrfs-progs.
*/
#include <dirent.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <stdint.h>
#include <linux/btrfs.h>
#include "mountP.h"
#include "bitops.h"
/* linux/btrfs.h lacks large parts of stuff needed for getting default
* sub-volume. Suppose that if BTRFS_DIR_ITEM_KEY is not defined, all
* declarations are still missing.
*/
#ifndef BTRFS_DIR_ITEM_KEY
/*
* dir items are the name -> inode pointers in a directory. There is one
* for every name in a directory.
*/
#define BTRFS_DIR_ITEM_KEY 84
/* holds pointers to all of the tree roots */
#define BTRFS_ROOT_TREE_OBJECTID 1ULL
/* directory objectid inside the root tree */
#define BTRFS_ROOT_TREE_DIR_OBJECTID 6ULL
/*
* the key defines the order in the tree, and so it also defines (optimal)
* block layout. objectid corresponds with the inode number. The flags
* tells us things about the object, and is a kind of stream selector.
* so for a given inode, keys with flags of 1 might refer to the inode
* data, flags of 2 may point to file data in the btree and flags == 3
* may point to extents.
*
* offset is the starting byte offset for this key in the stream.
*
* btrfs_disk_key is in disk byte order. struct btrfs_key is always
* in cpu native order. Otherwise they are identical and their sizes
* should be the same (ie both packed)
*/
struct btrfs_disk_key {
uint64_t objectid; /* little endian */
uint8_t type;
uint64_t offset; /* little endian */
} __attribute__ ((__packed__));
struct btrfs_dir_item {
struct btrfs_disk_key location;
uint64_t transid; /* little endian */
uint16_t data_len; /* little endian */
uint16_t name_len; /* little endian */
uint8_t type;
} __attribute__ ((__packed__));
#define BTRFS_SETGET_STACK_FUNCS(name, type, member, bits) \
static inline uint##bits##_t btrfs_##name(const type *s) \
{ \
return le##bits##_to_cpu(s->member); \
}
/* struct btrfs_disk_key */
BTRFS_SETGET_STACK_FUNCS(disk_key_objectid, struct btrfs_disk_key,
objectid, 64)
BTRFS_SETGET_STACK_FUNCS(stack_dir_name_len, struct btrfs_dir_item, name_len, 16)
/*
Red Black Trees
*/
struct rb_node {
unsigned long __rb_parent_color;
struct rb_node *rb_right;
struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
/* The alignment might seem pointless, but allegedly CRIS needs it */
#endif /* BTRFS_DIR_ITEM_KEY */
/*
* btrfs_get_default_subvol_id:
* @path: Path to mounted btrfs volume
*
* Searches for the btrfs default subvolume id.
*
* Returns: default subvolume id or UINT64_MAX (-1) in case of no
* default subvolume or error. In case of error, errno is set
* properly.
*/
uint64_t btrfs_get_default_subvol_id(const char *path)
{
int iocret;
int fd;
DIR *dirstream;
struct btrfs_ioctl_search_args args;
struct btrfs_ioctl_search_key *sk = &args.key;
struct btrfs_ioctl_search_header *sh;
uint64_t found = UINT64_MAX;
dirstream = opendir(path);
if (!dirstream) {
DBG(BTRFS, ul_debug("opendir() failed for \"%s\" [errno=%d %m]", path, errno));
return UINT64_MAX;
}
fd = dirfd(dirstream);
if (fd < 0) {
DBG(BTRFS, ul_debug("dirfd(opendir()) failed for \"%s\" [errno=%d %m]", path, errno));
goto out;
}
memset(&args, 0, sizeof(args));
sk->tree_id = BTRFS_ROOT_TREE_OBJECTID;
sk->min_objectid = BTRFS_ROOT_TREE_DIR_OBJECTID;
sk->max_objectid = BTRFS_ROOT_TREE_DIR_OBJECTID;
sk->min_type = BTRFS_DIR_ITEM_KEY;
sk->max_type = BTRFS_DIR_ITEM_KEY;
sk->max_offset = UINT64_MAX;
sk->max_transid = UINT64_MAX;
sk->nr_items = 1;
iocret = ioctl(fd, BTRFS_IOC_TREE_SEARCH, &args);
if (iocret < 0) {
DBG(BTRFS, ul_debug("ioctl() failed for \"%s\" [errno=%d %m]", path, errno));
goto out;
}
/* the ioctl returns the number of items it found in nr_items */
if (sk->nr_items == 0) {
DBG(BTRFS, ul_debug("root tree dir object id not found"));
goto out;
}
DBG(BTRFS, ul_debug("found %d root tree dir object id items", sk->nr_items));
sh = (struct btrfs_ioctl_search_header *)args.buf;
if (sh->type == BTRFS_DIR_ITEM_KEY) {
struct btrfs_dir_item *di;
int name_len;
char *name;
di = (struct btrfs_dir_item *)(sh + 1);
name_len = btrfs_stack_dir_name_len(di);
name = (char *)(di + 1);
if (!strncmp("default", name, name_len)) {
found = btrfs_disk_key_objectid(&di->location);
DBG(BTRFS, ul_debug("\"default\" id is %llu", (unsigned long long)found));
} else {
DBG(BTRFS, ul_debug("\"default\" id not found in tree root"));
goto out;
}
} else {
DBG(BTRFS, ul_debug("unexpected type found: %d", (int)sh->type));
goto out;
}
out:
closedir(dirstream);
return found;
}