dir_edit.c

/* AFS filesystem directory editing
 *
 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

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

/*
 * Find a number of contiguous clear bits in a directory block bitmask.
 *
 * There are 64 slots, which means we can load the entire bitmap into a
 * variable.  The first bit doesn't count as it corresponds to the block header
 * slot.  nr_slots is between 1 and 9.
 */
static int afs_find_contig_bits(union afs_xdr_dir_block *block, unsigned int nr_slots)
{
	u64 bitmap;
	u32 mask;
	int bit, n;

	bitmap  = (u64)block->hdr.bitmap[0] << 0 * 8;
	bitmap |= (u64)block->hdr.bitmap[1] << 1 * 8;
	bitmap |= (u64)block->hdr.bitmap[2] << 2 * 8;
	bitmap |= (u64)block->hdr.bitmap[3] << 3 * 8;
	bitmap |= (u64)block->hdr.bitmap[4] << 4 * 8;
	bitmap |= (u64)block->hdr.bitmap[5] << 5 * 8;
	bitmap |= (u64)block->hdr.bitmap[6] << 6 * 8;
	bitmap |= (u64)block->hdr.bitmap[7] << 7 * 8;
	bitmap >>= 1; /* The first entry is metadata */
	bit = 1;
	mask = (1 << nr_slots) - 1;

	do {
		if (sizeof(unsigned long) == 8)
			n = ffz(bitmap);
		else
			n = ((u32)bitmap) != 0 ?
				ffz((u32)bitmap) :
				ffz((u32)(bitmap >> 32)) + 32;
		bitmap >>= n;
		bit += n;

		if ((bitmap & mask) == 0) {
			if (bit > 64 - nr_slots)
				return -1;
			return bit;
		}

		n = __ffs(bitmap);
		bitmap >>= n;
		bit += n;
	} while (bitmap);

	return -1;
}

/*
 * Set a number of contiguous bits in the directory block bitmap.
 */
static void afs_set_contig_bits(union afs_xdr_dir_block *block,
				int bit, unsigned int nr_slots)
{
	u64 mask, before, after;

	mask = (1 << nr_slots) - 1;
	mask <<= bit;

	before = *(u64 *)block->hdr.bitmap;

	block->hdr.bitmap[0] |= (u8)(mask >> 0 * 8);
	block->hdr.bitmap[1] |= (u8)(mask >> 1 * 8);
	block->hdr.bitmap[2] |= (u8)(mask >> 2 * 8);
	block->hdr.bitmap[3] |= (u8)(mask >> 3 * 8);
	block->hdr.bitmap[4] |= (u8)(mask >> 4 * 8);
	block->hdr.bitmap[5] |= (u8)(mask >> 5 * 8);
	block->hdr.bitmap[6] |= (u8)(mask >> 6 * 8);
	block->hdr.bitmap[7] |= (u8)(mask >> 7 * 8);

	after = *(u64 *)block->hdr.bitmap;
}

/*
 * Clear a number of contiguous bits in the directory block bitmap.
 */
static void afs_clear_contig_bits(union afs_xdr_dir_block *block,
				  int bit, unsigned int nr_slots)
{
	u64 mask, before, after;

	mask = (1 << nr_slots) - 1;
	mask <<= bit;

	before = *(u64 *)block->hdr.bitmap;

	block->hdr.bitmap[0] &= ~(u8)(mask >> 0 * 8);
	block->hdr.bitmap[1] &= ~(u8)(mask >> 1 * 8);
	block->hdr.bitmap[2] &= ~(u8)(mask >> 2 * 8);
	block->hdr.bitmap[3] &= ~(u8)(mask >> 3 * 8);
	block->hdr.bitmap[4] &= ~(u8)(mask >> 4 * 8);
	block->hdr.bitmap[5] &= ~(u8)(mask >> 5 * 8);
	block->hdr.bitmap[6] &= ~(u8)(mask >> 6 * 8);
	block->hdr.bitmap[7] &= ~(u8)(mask >> 7 * 8);

	after = *(u64 *)block->hdr.bitmap;
}

/*
 * Scan a directory block looking for a dirent of the right name.
 */
static int afs_dir_scan_block(union afs_xdr_dir_block *block, struct qstr *name,
			      unsigned int blocknum)
{
	union afs_xdr_dirent *de;
	u64 bitmap;
	int d, len, n;

	_enter("");

	bitmap  = (u64)block->hdr.bitmap[0] << 0 * 8;
	bitmap |= (u64)block->hdr.bitmap[1] << 1 * 8;
	bitmap |= (u64)block->hdr.bitmap[2] << 2 * 8;
	bitmap |= (u64)block->hdr.bitmap[3] << 3 * 8;
	bitmap |= (u64)block->hdr.bitmap[4] << 4 * 8;
	bitmap |= (u64)block->hdr.bitmap[5] << 5 * 8;
	bitmap |= (u64)block->hdr.bitmap[6] << 6 * 8;
	bitmap |= (u64)block->hdr.bitmap[7] << 7 * 8;

	for (d = (blocknum == 0 ? AFS_DIR_RESV_BLOCKS0 : AFS_DIR_RESV_BLOCKS);
	     d < AFS_DIR_SLOTS_PER_BLOCK;
	     d++) {
		if (!((bitmap >> d) & 1))
			continue;
		de = &block->dirents[d];
		if (de->u.valid != 1)
			continue;

		/* The block was NUL-terminated by afs_dir_check_page(). */
		len = strlen(de->u.name);
		if (len == name->len &&
		    memcmp(de->u.name, name->name, name->len) == 0)
			return d;

		n = round_up(12 + len + 1 + 4, AFS_DIR_DIRENT_SIZE);
		n /= AFS_DIR_DIRENT_SIZE;
		d += n - 1;
	}

	return -1;
}

/*
 * Initialise a new directory block.  Note that block 0 is special and contains
 * some extra metadata.
 */
static void afs_edit_init_block(union afs_xdr_dir_block *meta,
				union afs_xdr_dir_block *block, int block_num)
{
	memset(block, 0, sizeof(*block));
	block->hdr.npages = htons(1);
	block->hdr.magic = AFS_DIR_MAGIC;
	block->hdr.bitmap[0] = 1;

	if (block_num == 0) {
		block->hdr.bitmap[0] = 0xff;
		block->hdr.bitmap[1] = 0x1f;
		memset(block->meta.alloc_ctrs,
		       AFS_DIR_SLOTS_PER_BLOCK,
		       sizeof(block->meta.alloc_ctrs));
		meta->meta.alloc_ctrs[0] =
			AFS_DIR_SLOTS_PER_BLOCK - AFS_DIR_RESV_BLOCKS0;
	}

	if (block_num < AFS_DIR_BLOCKS_WITH_CTR)
		meta->meta.alloc_ctrs[block_num] =
			AFS_DIR_SLOTS_PER_BLOCK - AFS_DIR_RESV_BLOCKS;
}

/*
 * Edit a directory's file data to add a new directory entry.  Doing this after
 * create, mkdir, symlink, link or rename if the data version number is
 * incremented by exactly one avoids the need to re-download the entire
 * directory contents.
 *
 * The caller must hold the inode locked.
 */
void afs_edit_dir_add(struct afs_vnode *vnode,
		      struct qstr *name, struct afs_fid *new_fid,
		      enum afs_edit_dir_reason why)
{
	union afs_xdr_dir_block *meta, *block;
	struct afs_xdr_dir_page *meta_page, *dir_page;
	union afs_xdr_dirent *de;
	struct page *page0, *page;
	unsigned int need_slots, nr_blocks, b;
	pgoff_t index;
	loff_t i_size;
	gfp_t gfp;
	int slot;

	_enter(",,{%d,%s},", name->len, name->name);

	i_size = i_size_read(&vnode->vfs_inode);
	if (i_size > AFS_DIR_BLOCK_SIZE * AFS_DIR_MAX_BLOCKS ||
	    (i_size & (AFS_DIR_BLOCK_SIZE - 1))) {
		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
		return;
	}

	gfp = vnode->vfs_inode.i_mapping->gfp_mask;
	page0 = find_or_create_page(vnode->vfs_inode.i_mapping, 0, gfp);
	if (!page0) {
		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
		_leave(" [fgp]");
		return;
	}

	/* Work out how many slots we're going to need. */
	need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE);
	need_slots /= AFS_DIR_DIRENT_SIZE;

	meta_page = kmap(page0);
	meta = &meta_page->blocks[0];
	if (i_size == 0)
		goto new_directory;
	nr_blocks = i_size / AFS_DIR_BLOCK_SIZE;

	/* Find a block that has sufficient slots available.  Each VM page
	 * contains two or more directory blocks.
	 */
	for (b = 0; b < nr_blocks + 1; b++) {
		/* If the directory extended into a new page, then we need to
		 * tack a new page on the end.
		 */
		index = b / AFS_DIR_BLOCKS_PER_PAGE;
		if (index == 0) {
			page = page0;
			dir_page = meta_page;
		} else {
			if (nr_blocks >= AFS_DIR_MAX_BLOCKS)
				goto error;
			gfp = vnode->vfs_inode.i_mapping->gfp_mask;
			page = find_or_create_page(vnode->vfs_inode.i_mapping,
						   index, gfp);
			if (!page)
				goto error;
			if (!PagePrivate(page)) {
				set_page_private(page, 1);
				SetPagePrivate(page);
			}
			dir_page = kmap(page);
		}

		/* Abandon the edit if we got a callback break. */
		if (!test_bit(AFS_VNODE_DIR_VALID, &vnode->flags))
			goto invalidated;

		block = &dir_page->blocks[b % AFS_DIR_BLOCKS_PER_PAGE];

		_debug("block %u: %2u %3u %u",
		       b,
		       (b < AFS_DIR_BLOCKS_WITH_CTR) ? meta->meta.alloc_ctrs[b] : 99,
		       ntohs(block->hdr.npages),
		       ntohs(block->hdr.magic));

		/* Initialise the block if necessary. */
		if (b == nr_blocks) {
			_debug("init %u", b);
			afs_edit_init_block(meta, block, b);
			i_size_write(&vnode->vfs_inode, (b + 1) * AFS_DIR_BLOCK_SIZE);
		}

		/* Only lower dir pages have a counter in the header. */
		if (b >= AFS_DIR_BLOCKS_WITH_CTR ||
		    meta->meta.alloc_ctrs[b] >= need_slots) {
			/* We need to try and find one or more consecutive
			 * slots to hold the entry.
			 */
			slot = afs_find_contig_bits(block, need_slots);
			if (slot >= 0) {
				_debug("slot %u", slot);
				goto found_space;
			}
		}

		if (page != page0) {
			unlock_page(page);
			kunmap(page);
			put_page(page);
		}
	}

	/* There are no spare slots of sufficient size, yet the operation
	 * succeeded.  Download the directory again.
	 */
	trace_afs_edit_dir(vnode, why, afs_edit_dir_create_nospc, 0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	goto out_unmap;

new_directory:
	afs_edit_init_block(meta, meta, 0);
	i_size = AFS_DIR_BLOCK_SIZE;
	i_size_write(&vnode->vfs_inode, i_size);
	slot = AFS_DIR_RESV_BLOCKS0;
	page = page0;
	block = meta;
	nr_blocks = 1;
	b = 0;

found_space:
	/* Set the dirent slot. */
	trace_afs_edit_dir(vnode, why, afs_edit_dir_create, b, slot,
			   new_fid->vnode, new_fid->unique, name->name);
	de = &block->dirents[slot];
	de->u.valid	= 1;
	de->u.unused[0]	= 0;
	de->u.hash_next	= 0; // TODO: Really need to maintain this
	de->u.vnode	= htonl(new_fid->vnode);
	de->u.unique	= htonl(new_fid->unique);
	memcpy(de->u.name, name->name, name->len + 1);
	de->u.name[name->len] = 0;

	/* Adjust the bitmap. */
	afs_set_contig_bits(block, slot, need_slots);
	if (page != page0) {
		unlock_page(page);
		kunmap(page);
		put_page(page);
	}

	/* Adjust the allocation counter. */
	if (b < AFS_DIR_BLOCKS_WITH_CTR)
		meta->meta.alloc_ctrs[b] -= need_slots;

	inode_inc_iversion_raw(&vnode->vfs_inode);
	afs_stat_v(vnode, n_dir_cr);
	_debug("Insert %s in %u[%u]", name->name, b, slot);

out_unmap:
	unlock_page(page0);
	kunmap(page0);
	put_page(page0);
	_leave("");
	return;

invalidated:
	trace_afs_edit_dir(vnode, why, afs_edit_dir_create_inval, 0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	if (page != page0) {
		kunmap(page);
		put_page(page);
	}
	goto out_unmap;

error:
	trace_afs_edit_dir(vnode, why, afs_edit_dir_create_error, 0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	goto out_unmap;
}

/*
 * Edit a directory's file data to remove a new directory entry.  Doing this
 * after unlink, rmdir or rename if the data version number is incremented by
 * exactly one avoids the need to re-download the entire directory contents.
 *
 * The caller must hold the inode locked.
 */
void afs_edit_dir_remove(struct afs_vnode *vnode,
			 struct qstr *name, enum afs_edit_dir_reason why)
{
	struct afs_xdr_dir_page *meta_page, *dir_page;
	union afs_xdr_dir_block *meta, *block;
	union afs_xdr_dirent *de;
	struct page *page0, *page;
	unsigned int need_slots, nr_blocks, b;
	pgoff_t index;
	loff_t i_size;
	int slot;

	_enter(",,{%d,%s},", name->len, name->name);

	i_size = i_size_read(&vnode->vfs_inode);
	if (i_size < AFS_DIR_BLOCK_SIZE ||
	    i_size > AFS_DIR_BLOCK_SIZE * AFS_DIR_MAX_BLOCKS ||
	    (i_size & (AFS_DIR_BLOCK_SIZE - 1))) {
		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
		return;
	}
	nr_blocks = i_size / AFS_DIR_BLOCK_SIZE;

	page0 = find_lock_page(vnode->vfs_inode.i_mapping, 0);
	if (!page0) {
		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
		_leave(" [fgp]");
		return;
	}

	/* Work out how many slots we're going to discard. */
	need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE);
	need_slots /= AFS_DIR_DIRENT_SIZE;

	meta_page = kmap(page0);
	meta = &meta_page->blocks[0];

	/* Find a page that has sufficient slots available.  Each VM page
	 * contains two or more directory blocks.
	 */
	for (b = 0; b < nr_blocks; b++) {
		index = b / AFS_DIR_BLOCKS_PER_PAGE;
		if (index != 0) {
			page = find_lock_page(vnode->vfs_inode.i_mapping, index);
			if (!page)
				goto error;
			dir_page = kmap(page);
		} else {
			page = page0;
			dir_page = meta_page;
		}

		/* Abandon the edit if we got a callback break. */
		if (!test_bit(AFS_VNODE_DIR_VALID, &vnode->flags))
			goto invalidated;

		block = &dir_page->blocks[b % AFS_DIR_BLOCKS_PER_PAGE];

		if (b > AFS_DIR_BLOCKS_WITH_CTR ||
		    meta->meta.alloc_ctrs[b] <= AFS_DIR_SLOTS_PER_BLOCK - 1 - need_slots) {
			slot = afs_dir_scan_block(block, name, b);
			if (slot >= 0)
				goto found_dirent;
		}

		if (page != page0) {
			unlock_page(page);
			kunmap(page);
			put_page(page);
		}
	}

	/* Didn't find the dirent to clobber.  Download the directory again. */
	trace_afs_edit_dir(vnode, why, afs_edit_dir_delete_noent,
			   0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	goto out_unmap;

found_dirent:
	de = &block->dirents[slot];

	trace_afs_edit_dir(vnode, why, afs_edit_dir_delete, b, slot,
			   ntohl(de->u.vnode), ntohl(de->u.unique),
			   name->name);

	memset(de, 0, sizeof(*de) * need_slots);

	/* Adjust the bitmap. */
	afs_clear_contig_bits(block, slot, need_slots);
	if (page != page0) {
		unlock_page(page);
		kunmap(page);
		put_page(page);
	}

	/* Adjust the allocation counter. */
	if (b < AFS_DIR_BLOCKS_WITH_CTR)
		meta->meta.alloc_ctrs[b] += need_slots;

	inode_set_iversion_raw(&vnode->vfs_inode, vnode->status.data_version);
	afs_stat_v(vnode, n_dir_rm);
	_debug("Remove %s from %u[%u]", name->name, b, slot);

out_unmap:
	unlock_page(page0);
	kunmap(page0);
	put_page(page0);
	_leave("");
	return;

invalidated:
	trace_afs_edit_dir(vnode, why, afs_edit_dir_delete_inval,
			   0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	if (page != page0) {
		unlock_page(page);
		kunmap(page);
		put_page(page);
	}
	goto out_unmap;

error:
	trace_afs_edit_dir(vnode, why, afs_edit_dir_delete_error,
			   0, 0, 0, 0, name->name);
	clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
	goto out_unmap;
}