fs/fat/nfs.c

/* fs/fat/nfs.c
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

#include <linux/exportfs.h>
#include "fat.h"

struct fat_fid {
	u32 i_gen;
	u32 i_pos_low;
	u16 i_pos_hi;
	u16 parent_i_pos_hi;
	u32 parent_i_pos_low;
	u32 parent_i_gen;
};

#define FAT_FID_SIZE_WITHOUT_PARENT 3
#define FAT_FID_SIZE_WITH_PARENT (sizeof(struct fat_fid)/sizeof(u32))

/**
 * Look up a directory inode given its starting cluster.
 */
static struct inode *fat_dget(struct super_block *sb, int i_logstart)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct hlist_head *head;
	struct msdos_inode_info *i;
	struct inode *inode = NULL;

	head = sbi->dir_hashtable + fat_dir_hash(i_logstart);
	spin_lock(&sbi->dir_hash_lock);
	hlist_for_each_entry(i, head, i_dir_hash) {
		BUG_ON(i->vfs_inode.i_sb != sb);
		if (i->i_logstart != i_logstart)
			continue;
		inode = igrab(&i->vfs_inode);
		if (inode)
			break;
	}
	spin_unlock(&sbi->dir_hash_lock);
	return inode;
}

static struct inode *__fat_nfs_get_inode(struct super_block *sb,
				       u64 ino, u32 generation, loff_t i_pos)
{
	struct inode *inode;

	if ((ino < MSDOS_ROOT_INO) || (ino == MSDOS_FSINFO_INO))
		return NULL;

	inode = ilookup(sb, ino);
	if (inode && generation && (inode->i_generation != generation)) {
		iput(inode);
		inode = NULL;
	}

	return inode;
}

static struct inode *fat_nfs_get_inode(struct super_block *sb,
				       u64 ino, u32 generation)
{

	return __fat_nfs_get_inode(sb, ino, generation, 0);
}

static int
fat_encode_fh_nostale(struct inode *inode, __u32 *fh, int *lenp,
		      struct inode *parent)
{
	int len = *lenp;
	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
	struct fat_fid *fid = (struct fat_fid *) fh;
	loff_t i_pos;
	int type = FILEID_FAT_WITHOUT_PARENT;

	if (parent) {
		if (len < FAT_FID_SIZE_WITH_PARENT) {
			*lenp = FAT_FID_SIZE_WITH_PARENT;
			return FILEID_INVALID;
		}
	} else {
		if (len < FAT_FID_SIZE_WITHOUT_PARENT) {
			*lenp = FAT_FID_SIZE_WITHOUT_PARENT;
			return FILEID_INVALID;
		}
	}

	i_pos = fat_i_pos_read(sbi, inode);
	*lenp = FAT_FID_SIZE_WITHOUT_PARENT;
	fid->i_gen = inode->i_generation;
	fid->i_pos_low = i_pos & 0xFFFFFFFF;
	fid->i_pos_hi = (i_pos >> 32) & 0xFFFF;
	if (parent) {
		i_pos = fat_i_pos_read(sbi, parent);
		fid->parent_i_pos_hi = (i_pos >> 32) & 0xFFFF;
		fid->parent_i_pos_low = i_pos & 0xFFFFFFFF;
		fid->parent_i_gen = parent->i_generation;
		type = FILEID_FAT_WITH_PARENT;
		*lenp = FAT_FID_SIZE_WITH_PARENT;
	}

	return type;
}

/**
 * Map a NFS file handle to a corresponding dentry.
 * The dentry may or may not be connected to the filesystem root.
 */
static struct dentry *fat_fh_to_dentry(struct super_block *sb, struct fid *fid,
				int fh_len, int fh_type)
{
	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
				    fat_nfs_get_inode);
}

static struct dentry *fat_fh_to_dentry_nostale(struct super_block *sb,
					       struct fid *fh, int fh_len,
					       int fh_type)
{
	struct inode *inode = NULL;
	struct fat_fid *fid = (struct fat_fid *)fh;
	loff_t i_pos;

	switch (fh_type) {
	case FILEID_FAT_WITHOUT_PARENT:
		if (fh_len < FAT_FID_SIZE_WITHOUT_PARENT)
			return NULL;
		break;
	case FILEID_FAT_WITH_PARENT:
		if (fh_len < FAT_FID_SIZE_WITH_PARENT)
			return NULL;
		break;
	default:
		return NULL;
	}
	i_pos = fid->i_pos_hi;
	i_pos = (i_pos << 32) | (fid->i_pos_low);
	inode = __fat_nfs_get_inode(sb, 0, fid->i_gen, i_pos);

	return d_obtain_alias(inode);
}

/*
 * Find the parent for a file specified by NFS handle.
 * This requires that the handle contain the i_ino of the parent.
 */
static struct dentry *fat_fh_to_parent(struct super_block *sb, struct fid *fid,
				int fh_len, int fh_type)
{
	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
				    fat_nfs_get_inode);
}

static struct dentry *fat_fh_to_parent_nostale(struct super_block *sb,
					       struct fid *fh, int fh_len,
					       int fh_type)
{
	struct inode *inode = NULL;
	struct fat_fid *fid = (struct fat_fid *)fh;
	loff_t i_pos;

	if (fh_len < FAT_FID_SIZE_WITH_PARENT)
		return NULL;

	switch (fh_type) {
	case FILEID_FAT_WITH_PARENT:
		i_pos = fid->parent_i_pos_hi;
		i_pos = (i_pos << 32) | (fid->parent_i_pos_low);
		inode = __fat_nfs_get_inode(sb, 0, fid->parent_i_gen, i_pos);
		break;
	}

	return d_obtain_alias(inode);
}

/*
 * Find the parent for a directory that is not currently connected to
 * the filesystem root.
 *
 * On entry, the caller holds child_dir->d_inode->i_mutex.
 */
static struct dentry *fat_get_parent(struct dentry *child_dir)
{
	struct super_block *sb = child_dir->d_sb;
	struct buffer_head *bh = NULL;
	struct msdos_dir_entry *de;
	struct inode *parent_inode = NULL;

	if (!fat_get_dotdot_entry(child_dir->d_inode, &bh, &de)) {
		int parent_logstart = fat_get_start(MSDOS_SB(sb), de);
		parent_inode = fat_dget(sb, parent_logstart);
	}
	brelse(bh);

	return d_obtain_alias(parent_inode);
}

const struct export_operations fat_export_ops = {
	.fh_to_dentry   = fat_fh_to_dentry,
	.fh_to_parent   = fat_fh_to_parent,
	.get_parent     = fat_get_parent,
};

const struct export_operations fat_export_ops_nostale = {
	.encode_fh      = fat_encode_fh_nostale,
	.fh_to_dentry   = fat_fh_to_dentry_nostale,
	.fh_to_parent   = fat_fh_to_parent_nostale,
	.get_parent     = fat_get_parent,
};