linux/fs/afs/dir_search.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Search a directory's hash table.
 *
 * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * https://tools.ietf.org/html/draft-keiser-afs3-directory-object-00
 */

#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/iversion.h>
#include "internal.h"
#include "afs_fs.h"
#include "xdr_fs.h"

/*
 * Calculate the name hash.
 */
unsigned int afs_dir_hash_name(const struct qstr *name)
{
	const unsigned char *p = name->name;
	unsigned int hash = 0, i;
	int bucket;

	for (i = 0; i < name->len; i++)
		hash = (hash * 173) + p[i];
	bucket = hash & (AFS_DIR_HASHTBL_SIZE - 1);
	if (hash > INT_MAX) {
		bucket = AFS_DIR_HASHTBL_SIZE - bucket;
		bucket &= (AFS_DIR_HASHTBL_SIZE - 1);
	}
	return bucket;
}

/*
 * Reset a directory iterator.
 */
static bool afs_dir_reset_iter(struct afs_dir_iter *iter)
{
	unsigned long long i_size = i_size_read(&iter->dvnode->netfs.inode);
	unsigned int nblocks;

	/* Work out the maximum number of steps we can take. */
	nblocks = umin(i_size / AFS_DIR_BLOCK_SIZE, AFS_DIR_MAX_BLOCKS);
	if (!nblocks)
		return false;
	iter->loop_check = nblocks * (AFS_DIR_SLOTS_PER_BLOCK - AFS_DIR_RESV_BLOCKS);
	iter->prev_entry = 0; /* Hash head is previous */
	return true;
}

/*
 * Initialise a directory iterator for looking up a name.
 */
bool afs_dir_init_iter(struct afs_dir_iter *iter, const struct qstr *name)
{
	iter->nr_slots = afs_dir_calc_slots(name->len);
	iter->bucket = afs_dir_hash_name(name);
	return afs_dir_reset_iter(iter);
}

/*
 * Get a specific block.
 */
union afs_xdr_dir_block *afs_dir_find_block(struct afs_dir_iter *iter, size_t block)
{
	struct folio_queue *fq = iter->fq;
	struct afs_vnode *dvnode = iter->dvnode;
	struct folio *folio;
	size_t blpos = block * AFS_DIR_BLOCK_SIZE;
	size_t blend = (block + 1) * AFS_DIR_BLOCK_SIZE, fpos = iter->fpos;
	int slot = iter->fq_slot;

	_enter("%zx,%d", block, slot);

	if (iter->block) {
		kunmap_local(iter->block);
		iter->block = NULL;
	}

	if (dvnode->directory_size < blend)
		goto fail;

	if (!fq || blpos < fpos) {
		fq = dvnode->directory;
		slot = 0;
		fpos = 0;
	}

	/* Search the folio queue for the folio containing the block... */
	for (; fq; fq = fq->next) {
		for (; slot < folioq_count(fq); slot++) {
			size_t fsize = folioq_folio_size(fq, slot);

			if (blend <= fpos + fsize) {
				/* ... and then return the mapped block. */
				folio = folioq_folio(fq, slot);
				if (WARN_ON_ONCE(folio_pos(folio) != fpos))
					goto fail;
				iter->fq = fq;
				iter->fq_slot = slot;
				iter->fpos = fpos;
				iter->block = kmap_local_folio(folio, blpos - fpos);
				return iter->block;
			}
			fpos += fsize;
		}
		slot = 0;
	}

fail:
	iter->fq = NULL;
	iter->fq_slot = 0;
	afs_invalidate_dir(dvnode, afs_dir_invalid_edit_get_block);
	return NULL;
}

/*
 * Search through a directory bucket.
 */
int afs_dir_search_bucket(struct afs_dir_iter *iter, const struct qstr *name,
			  struct afs_fid *_fid)
{
	const union afs_xdr_dir_block *meta;
	unsigned int entry;
	int ret = -ESTALE;

	meta = afs_dir_find_block(iter, 0);
	if (!meta)
		return -ESTALE;

	entry = ntohs(meta->meta.hashtable[iter->bucket & (AFS_DIR_HASHTBL_SIZE - 1)]);
	_enter("%x,%x", iter->bucket, entry);

	while (entry) {
		const union afs_xdr_dir_block *block;
		const union afs_xdr_dirent *dire;
		unsigned int blnum = entry / AFS_DIR_SLOTS_PER_BLOCK;
		unsigned int slot = entry % AFS_DIR_SLOTS_PER_BLOCK;
		unsigned int resv = (blnum == 0 ? AFS_DIR_RESV_BLOCKS0 : AFS_DIR_RESV_BLOCKS);

		_debug("search %x", entry);

		if (slot < resv) {
			kdebug("slot out of range h=%x rs=%2x sl=%2x-%2x",
			       iter->bucket, resv, slot, slot + iter->nr_slots - 1);
			goto bad;
		}

		block = afs_dir_find_block(iter, blnum);
		if (!block)
			goto bad;
		dire = &block->dirents[slot];

		if (slot + iter->nr_slots <= AFS_DIR_SLOTS_PER_BLOCK &&
		    memcmp(dire->u.name, name->name, name->len) == 0 &&
		    dire->u.name[name->len] == '\0') {
			_fid->vnode  = ntohl(dire->u.vnode);
			_fid->unique = ntohl(dire->u.unique);
			ret = entry;
			goto found;
		}

		iter->prev_entry = entry;
		entry = ntohs(dire->u.hash_next);
		if (!--iter->loop_check) {
			kdebug("dir chain loop h=%x", iter->bucket);
			goto bad;
		}
	}

	ret = -ENOENT;
found:
	if (iter->block) {
		kunmap_local(iter->block);
		iter->block = NULL;
	}

bad:
	if (ret == -ESTALE)
		afs_invalidate_dir(iter->dvnode, afs_dir_invalid_iter_stale);
	_leave(" = %d", ret);
	return ret;
}

/*
 * Search the appropriate hash chain in the contents of an AFS directory.
 */
int afs_dir_search(struct afs_vnode *dvnode, struct qstr *name,
		   struct afs_fid *_fid, afs_dataversion_t *_dir_version)
{
	struct afs_dir_iter iter = { .dvnode = dvnode, };
	int ret, retry_limit = 3;

	_enter("{%lu},,,", dvnode->netfs.inode.i_ino);

	if (!afs_dir_init_iter(&iter, name))
		return -ENOENT;
	do {
		if (--retry_limit < 0) {
			pr_warn("afs_read_dir(): Too many retries\n");
			ret = -ESTALE;
			break;
		}
		ret = afs_read_dir(dvnode, NULL);
		if (ret < 0) {
			if (ret != -ESTALE)
				break;
			if (test_bit(AFS_VNODE_DELETED, &dvnode->flags)) {
				ret = -ESTALE;
				break;
			}
			continue;
		}
		*_dir_version = inode_peek_iversion_raw(&dvnode->netfs.inode);

		ret = afs_dir_search_bucket(&iter, name, _fid);
		up_read(&dvnode->validate_lock);
		if (ret == -ESTALE)
			afs_dir_reset_iter(&iter);
	} while (ret == -ESTALE);

	_leave(" = %d", ret);
	return ret;
}