/**
@file     file_handle_tools.h
@brief    Tools for creating and working with file handles
@details  Copyright (c) 2024 Acronis International GmbH
@author   Bruce Wang ([email protected])
@since    $Id: $
*/

#pragma once

#include "compat.h"
#include "memory.h"

typedef struct {
  uint32_t handle_bytes;
  int handle_type;
  int mnt_id;
  unsigned char* f_handle;
} file_handle_info_t;

#ifndef BPF_PROGRAM

// init_empty initialize message enough so 'free' can work
static inline void file_handle_info_init_empty(file_handle_info_t* info)
{
	info->f_handle = NULL;
}

// It is a bit counterintuitive but 'info->mnt_id' is always filled in despite the return value.
// If 'f_handle' is non-null, it can be used
static inline int file_handle_info_make_with_alloc_flags(file_handle_info_t* info, const struct path *path, bool nowait)
{
	int dwords = MAX_HANDLE_SZ >> 2;
	struct dentry *dentry = path->dentry;
	struct vfsmount* mnt = path->mnt;

	info->mnt_id = mnt ? get_mnt_id(mnt) : 0;
	info->f_handle = NULL;
	info->handle_bytes = 0;

#ifdef HAVE_EXPORTFS_ENCODE_INODE_FH
	if (!dentry || !dentry->d_inode || !dentry->d_inode->i_sb || !dentry->d_inode->i_sb->s_export_op) {
		return -EFAULT;
	}
#else
	if (!dentry || !dentry->d_sb || !dentry->d_sb->s_export_op) {
		return -EFAULT;
	}
#endif

	info->f_handle = kmem_cache_alloc(g_handles_cache, mem_flags(nowait));
	if (!info->f_handle) {
		return -ENOMEM;
	}

	// Returns an enum fid_type or a negative on errno.
	info->handle_type = exportfs_encode_fh(dentry, (struct fid *)info->f_handle, &dwords, 0);
	if (info->handle_type < 0) {
		goto err;
	}

	info->handle_bytes = dwords * sizeof(u32);
	return 0;

err:
	kmem_cache_free(g_handles_cache, info->f_handle);
	info->f_handle = NULL;
	return info->handle_type;
}

static inline int file_handle_info_make(file_handle_info_t* info, const struct path *path)
{
	return file_handle_info_make_with_alloc_flags(info, path, false /*nowait*/);
}

static inline int file_handle_info_make_nowait(file_handle_info_t* info, const struct path *path)
{
	return file_handle_info_make_with_alloc_flags(info, path, true /*nowait*/);
}

static inline void file_handle_info_free(file_handle_info_t* info) {
	if (info->f_handle) {
		kmem_cache_free(g_handles_cache, info->f_handle);
	}
}

#endif