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