// SPDX-License-Identifier: GPL-2.0-only

  /* fs/fat/nfs.c

   */
  
  #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_ilookup(struct super_block *sb, u64 ino, loff_t i_pos)
  {
  	if (MSDOS_SB(sb)->options.nfs == FAT_NFS_NOSTALE_RO)
  		return fat_iget(sb, i_pos);
  
  	else {
  		if ((ino < MSDOS_ROOT_INO) || (ino == MSDOS_FSINFO_INO))
  			return NULL;
  		return ilookup(sb, ino);
  	}
  }

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

  {

  	struct inode *inode = fat_ilookup(sb, ino, i_pos);

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

  	if (inode == NULL && MSDOS_SB(sb)->options.nfs == FAT_NFS_NOSTALE_RO) {
  		struct buffer_head *bh = NULL;
  		struct msdos_dir_entry *de ;
  		sector_t blocknr;
  		int offset;
  		fat_get_blknr_offset(MSDOS_SB(sb), i_pos, &blocknr, &offset);
  		bh = sb_bread(sb, blocknr);
  		if (!bh) {
  			fat_msg(sb, KERN_ERR,
  				"unable to read block(%llu) for building NFS inode",
  				(llu)blocknr);
  			return inode;
  		}
  		de = (struct msdos_dir_entry *)bh->b_data;
  		/* If a file is deleted on server and client is not updated
  		 * yet, we must not build the inode upon a lookup call.
  		 */
  		if (IS_FREE(de[offset].name))
  			inode = NULL;
  		else
  			inode = fat_build_inode(sb, &de[offset], i_pos);
  		brelse(bh);
  	}

  
  	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);
  }

  /*

   * Rebuild the parent for a directory that is not connected
   *  to the filesystem root
   */
  static
  struct inode *fat_rebuild_parent(struct super_block *sb, int parent_logstart)
  {
  	int search_clus, clus_to_match;
  	struct msdos_dir_entry *de;
  	struct inode *parent = NULL;
  	struct inode *dummy_grand_parent = NULL;
  	struct fat_slot_info sinfo;
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	sector_t blknr = fat_clus_to_blknr(sbi, parent_logstart);
  	struct buffer_head *parent_bh = sb_bread(sb, blknr);
  	if (!parent_bh) {
  		fat_msg(sb, KERN_ERR,
  			"unable to read cluster of parent directory");
  		return NULL;
  	}
  
  	de = (struct msdos_dir_entry *) parent_bh->b_data;
  	clus_to_match = fat_get_start(sbi, &de[0]);
  	search_clus = fat_get_start(sbi, &de[1]);
  
  	dummy_grand_parent = fat_dget(sb, search_clus);
  	if (!dummy_grand_parent) {
  		dummy_grand_parent = new_inode(sb);
  		if (!dummy_grand_parent) {
  			brelse(parent_bh);
  			return parent;
  		}
  
  		dummy_grand_parent->i_ino = iunique(sb, MSDOS_ROOT_INO);
  		fat_fill_inode(dummy_grand_parent, &de[1]);
  		MSDOS_I(dummy_grand_parent)->i_pos = -1;
  	}
  
  	if (!fat_scan_logstart(dummy_grand_parent, clus_to_match, &sinfo))
  		parent = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
  
  	brelse(parent_bh);
  	iput(dummy_grand_parent);
  
  	return parent;
  }
  
  /*

   * Find the parent for a directory that is not currently connected to
   * the filesystem root.
   *

   * On entry, the caller holds d_inode(child_dir)->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;

  	struct msdos_sb_info *sbi = MSDOS_SB(sb);

  	if (!fat_get_dotdot_entry(d_inode(child_dir), &bh, &de)) {

  		int parent_logstart = fat_get_start(sbi, de);

  		parent_inode = fat_dget(sb, parent_logstart);

  		if (!parent_inode && sbi->options.nfs == FAT_NFS_NOSTALE_RO)
  			parent_inode = fat_rebuild_parent(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,
  };