// 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;
        } else {
                /*
                 * We need to initialize this field because the fh is actually
                 * 12 bytes long
                 */
                fid->parent_i_pos_hi = 0;
        }

        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 = {
        .encode_fh      = generic_encode_ino32_fh,
        .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,
};