path: root/fs/nfs/internal.h

/*
 * NFS internal definitions
 */

#include "nfs4_fs.h"
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/crc32.h>

#define NFS_MS_MASK (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_SYNCHRONOUS)

struct nfs_string;

/* Maximum number of readahead requests
 * FIXME: this should really be a sysctl so that users may tune it to suit
 *        their needs. People that do NFS over a slow network, might for
 *        instance want to reduce it to something closer to 1 for improved
 *        interactive response.
 */
#define NFS_MAX_READAHEAD	(RPC_DEF_SLOT_TABLE - 1)

static inline void nfs_attr_check_mountpoint(struct super_block *parent, struct nfs_fattr *fattr)
{
	if (!nfs_fsid_equal(&NFS_SB(parent)->fsid, &fattr->fsid))
		fattr->valid |= NFS_ATTR_FATTR_MOUNTPOINT;
}

static inline int nfs_attr_use_mounted_on_fileid(struct nfs_fattr *fattr)
{
	if (((fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID) == 0) ||
	    (((fattr->valid & NFS_ATTR_FATTR_MOUNTPOINT) == 0) &&
	     ((fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL) == 0)))
		return 0;

	fattr->fileid = fattr->mounted_on_fileid;
	return 1;
}

struct nfs_clone_mount {
	const struct super_block *sb;
	const struct dentry *dentry;
	struct nfs_fh *fh;
	struct nfs_fattr *fattr;
	char *hostname;
	char *mnt_path;
	struct sockaddr *addr;
	size_t addrlen;
	rpc_authflavor_t authflavor;
};

/*
 * Note: RFC 1813 doesn't limit the number of auth flavors that
 * a server can return, so make something up.
 */
#define NFS_MAX_SECFLAVORS	(12)

/*
 * Value used if the user did not specify a port value.
 */
#define NFS_UNSPEC_PORT		(-1)

/*
 * Maximum number of pages that readdir can use for creating
 * a vmapped array of pages.
 */
#define NFS_MAX_READDIR_PAGES 8

struct nfs_client_initdata {
	unsigned long init_flags;
	const char *hostname;
	const struct sockaddr *addr;
	size_t addrlen;
	struct nfs_subversion *nfs_mod;
	int proto;
	u32 minorversion;
	struct net *net;
};

/*
 * In-kernel mount arguments
 */
struct nfs_parsed_mount_data {
	int			flags;
	unsigned int		rsize, wsize;
	unsigned int		timeo, retrans;
	unsigned int		acregmin, acregmax,
				acdirmin, acdirmax;
	unsigned int		namlen;
	unsigned int		options;
	unsigned int		bsize;
	struct nfs_auth_info	auth_info;
	rpc_authflavor_t	selected_flavor;
	char			*client_address;
	unsigned int		version;
	unsigned int		minorversion;
	char			*fscache_uniq;
	bool			need_mount;

	struct {
		struct sockaddr_storage	address;
		size_t			addrlen;
		char			*hostname;
		u32			version;
		int			port;
		unsigned short		protocol;
	} mount_server;

	struct {
		struct sockaddr_storage	address;
		size_t			addrlen;
		char			*hostname;
		char			*export_path;
		int			port;
		unsigned short		protocol;
	} nfs_server;

	struct security_mnt_opts lsm_opts;
	struct net		*net;
};

/* mount_clnt.c */
struct nfs_mount_request {
	struct sockaddr		*sap;
	size_t			salen;
	char			*hostname;
	char			*dirpath;
	u32			version;
	unsigned short		protocol;
	struct nfs_fh		*fh;
	int			noresvport;
	unsigned int		*auth_flav_len;
	rpc_authflavor_t	*auth_flavs;
	struct net		*net;
};

struct nfs_mount_info {
	void (*fill_super)(struct super_block *, struct nfs_mount_info *);
	int (*set_security)(struct super_block *, struct dentry *, struct nfs_mount_info *);
	struct nfs_parsed_mount_data *parsed;
	struct nfs_clone_mount *cloned;
	struct nfs_fh *mntfh;
};

extern int nfs_mount(struct nfs_mount_request *info);
extern void nfs_umount(const struct nfs_mount_request *info);

/* client.c */
extern const struct rpc_program nfs_program;
extern void nfs_clients_init(struct net *net);
extern struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *);
int nfs_create_rpc_client(struct nfs_client *, const struct rpc_timeout *, rpc_authflavor_t);
struct nfs_client *nfs_get_client(const struct nfs_client_initdata *,
				  const struct rpc_timeout *, const char *,
				  rpc_authflavor_t);
int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *, struct nfs_fattr *);
void nfs_server_insert_lists(struct nfs_server *);
void nfs_server_remove_lists(struct nfs_server *);
void nfs_init_timeout_values(struct rpc_timeout *, int, unsigned int, unsigned int);
int nfs_init_server_rpcclient(struct nfs_server *, const struct rpc_timeout *t,
		rpc_authflavor_t);
struct nfs_server *nfs_alloc_server(void);
void nfs_server_copy_userdata(struct nfs_server *, struct nfs_server *);

extern void nfs_cleanup_cb_ident_idr(struct net *);
extern void nfs_put_client(struct nfs_client *);
extern void nfs_free_client(struct nfs_client *);
extern struct nfs_client *nfs4_find_client_ident(struct net *, int);
extern struct nfs_client *
nfs4_find_client_sessionid(struct net *, const struct sockaddr *,
				struct nfs4_sessionid *, u32);
extern struct nfs_server *nfs_create_server(struct nfs_mount_info *,
					struct nfs_subversion *);
extern struct nfs_server *nfs4_create_server(
					struct nfs_mount_info *,
					struct nfs_subversion *);
extern struct nfs_server *nfs4_create_referral_server(struct nfs_clone_mount *,
						      struct nfs_fh *);
extern int nfs4_update_server(struct nfs_server *server, const char *hostname,
					struct sockaddr *sap, size_t salen,
					struct net *net);
extern void nfs_free_server(struct nfs_server *server);
extern struct nfs_server *nfs_clone_server(struct nfs_server *,
					   struct nfs_fh *,
					   struct nfs_fattr *,
					   rpc_authflavor_t);
extern int nfs_wait_client_init_complete(const struct nfs_client *clp);
extern void nfs_mark_client_ready(struct nfs_client *clp, int state);
extern struct nfs_client *nfs4_set_ds_client(struct nfs_client* mds_clp,
					     const struct sockaddr *ds_addr,
					     int ds_addrlen, int ds_proto,
					     unsigned int ds_timeo,
					     unsigned int ds_retrans);
extern struct rpc_clnt *nfs4_find_or_create_ds_client(struct nfs_client *,
						struct inode *);
#ifdef CONFIG_PROC_FS
extern int __init nfs_fs_proc_init(void);
extern void nfs_fs_proc_exit(void);
#else
static inline int nfs_fs_proc_init(void)
{
	return 0;
}
static inline void nfs_fs_proc_exit(void)
{
}
#endif

#ifdef CONFIG_NFS_V4_1
int nfs_sockaddr_match_ipaddr(const struct sockaddr *, const struct sockaddr *);
#endif

/* nfs3client.c */
#if IS_ENABLED(CONFIG_NFS_V3)
struct nfs_server *nfs3_create_server(struct nfs_mount_info *, struct nfs_subversion *);
struct nfs_server *nfs3_clone_server(struct nfs_server *, struct nfs_fh *,
				     struct nfs_fattr *, rpc_authflavor_t);
#endif

/* callback_xdr.c */
extern struct svc_version nfs4_callback_version1;
extern struct svc_version nfs4_callback_version4;

struct nfs_pageio_descriptor;
/* pagelist.c */
extern int __init nfs_init_nfspagecache(void);
extern void nfs_destroy_nfspagecache(void);
extern int __init nfs_init_readpagecache(void);
extern void nfs_destroy_readpagecache(void);
extern int __init nfs_init_writepagecache(void);
extern void nfs_destroy_writepagecache(void);

extern int __init nfs_init_directcache(void);
extern void nfs_destroy_directcache(void);
extern void nfs_pgheader_init(struct nfs_pageio_descriptor *desc,
			      struct nfs_pgio_header *hdr,
			      void (*release)(struct nfs_pgio_header *hdr));
void nfs_set_pgio_error(struct nfs_pgio_header *hdr, int error, loff_t pos);
int nfs_iocounter_wait(struct nfs_io_counter *c);

struct nfs_rw_header *nfs_rw_header_alloc(const struct nfs_rw_ops *);
void nfs_rw_header_free(struct nfs_pgio_header *);
void nfs_pgio_data_release(struct nfs_pgio_data *);
int nfs_generic_pgio(struct nfs_pageio_descriptor *, struct nfs_pgio_header *);
int nfs_initiate_pgio(struct rpc_clnt *, struct nfs_pgio_data *,
		      const struct rpc_call_ops *, int, int);

static inline void nfs_iocounter_init(struct nfs_io_counter *c)
{
	c->flags = 0;
	atomic_set(&c->io_count, 0);
}

/* nfs2xdr.c */
extern struct rpc_procinfo nfs_procedures[];
extern int nfs2_decode_dirent(struct xdr_stream *,
				struct nfs_entry *, int);

/* nfs3xdr.c */
extern struct rpc_procinfo nfs3_procedures[];
extern int nfs3_decode_dirent(struct xdr_stream *,
				struct nfs_entry *, int);

/* nfs4xdr.c */
#if IS_ENABLED(CONFIG_NFS_V4)
extern int nfs4_decode_dirent(struct xdr_stream *,
				struct nfs_entry *, int);
#endif
#ifdef CONFIG_NFS_V4_1
extern const u32 nfs41_maxread_overhead;
extern const u32 nfs41_maxwrite_overhead;
extern const u32 nfs41_maxgetdevinfo_overhead;
#endif

/* nfs4proc.c */
#if IS_ENABLED(CONFIG_NFS_V4)
extern struct rpc_procinfo nfs4_procedures[];
#endif

#ifdef CONFIG_NFS_V4_SECURITY_LABEL
extern struct nfs4_label *nfs4_label_alloc(struct nfs_server *server, gfp_t flags);
static inline void nfs4_label_free(struct nfs4_label *label)
{
	if (label) {
		kfree(label->label);
		kfree(label);
	}
	return;
}

static inline void nfs_zap_label_cache_locked(struct nfs_inode *nfsi)
{
	if (nfs_server_capable(&nfsi->vfs_inode, NFS_CAP_SECURITY_LABEL))
		nfsi->cache_validity |= NFS_INO_INVALID_LABEL;
}
#else
static inline struct nfs4_label *nfs4_label_alloc(struct nfs_server *server, gfp_t flags) { return NULL; }
static inline void nfs4_label_free(void *label) {}
static inline void nfs_zap_label_cache_locked(struct nfs_inode *nfsi)
{
}
#endif /* CONFIG_NFS_V4_SECURITY_LABEL */

/* proc.c */
void nfs_close_context(struct nfs_open_context *ctx, int is_sync);
extern struct nfs_client *nfs_init_client(struct nfs_client *clp,
			   const struct rpc_timeout *timeparms,
			   const char *ip_addr);

/* dir.c */
extern void nfs_force_use_readdirplus(struct inode *dir);
extern unsigned long nfs_access_cache_count(struct shrinker *shrink,
					    struct shrink_control *sc);
extern unsigned long nfs_access_cache_scan(struct shrinker *shrink,
					   struct shrink_control *sc);
struct dentry *nfs_lookup(struct inode *, struct dentry *, unsigned int);
int nfs_create(struct inode *, struct dentry *, umode_t, bool);
int nfs_mkdir(struct inode *, struct dentry *, umode_t);
int nfs_rmdir(struct inode *, struct dentry *);
int nfs_unlink(struct inode *, struct dentry *);
int nfs_symlink(struct inode *, struct dentry *, const char *);
int nfs_link(struct dentry *, struct inode *, struct dentry *);
int nfs_mknod(struct inode *, struct dentry *, umode_t, dev_t);
int nfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);

/* file.c */
int nfs_file_fsync_commit(struct file *, loff_t, loff_t, int);
loff_t nfs_file_llseek(struct file *, loff_t, int);
int nfs_file_flush(struct file *, fl_owner_t);
ssize_t nfs_file_read(struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t nfs_file_splice_read(struct file *, loff_t *, struct pipe_inode_info *,
			     size_t, unsigned int);
int nfs_file_mmap(struct file *, struct vm_area_struct *);
ssize_t nfs_file_write(struct kiocb *, const struct iovec *, unsigned long, loff_t);
int nfs_file_release(struct inode *, struct file *);
int nfs_lock(struct file *, int, struct file_lock *);
int nfs_flock(struct file *, int, struct file_lock *);
ssize_t nfs_file_splice_write(struct pipe_inode_info *, struct file *, loff_t *,
			      size_t, unsigned int);
int nfs_check_flags(int);
int nfs_setlease(struct file *, long, struct file_lock **);

/* inode.c */
extern struct workqueue_struct *nfsiod_workqueue;
extern struct inode *nfs_alloc_inode(struct super_block *sb);
extern void nfs_destroy_inode(struct inode *);
extern int nfs_write_inode(struct inode *, struct writeback_control *);
extern int nfs_drop_inode(struct inode *);
extern void nfs_clear_inode(struct inode *);
extern void nfs_evict_inode(struct inode *);
void nfs_zap_acl_cache(struct inode *inode);
extern int nfs_wait_bit_killable(void *word);

/* super.c */
extern const struct super_operations nfs_sops;
extern struct file_system_type nfs_fs_type;
extern struct file_system_type nfs_xdev_fs_type;
#if IS_ENABLED(CONFIG_NFS_V4)
extern struct file_system_type nfs4_xdev_fs_type;
extern struct file_system_type nfs4_referral_fs_type;
#endif
bool nfs_auth_info_match(const struct nfs_auth_info *, rpc_authflavor_t);
struct dentry *nfs_try_mount(int, const char *, struct nfs_mount_info *,
			struct nfs_subversion *);
void nfs_initialise_sb(struct super_block *);
int nfs_set_sb_security(struct super_block *, struct dentry *, struct nfs_mount_info *);
int nfs_clone_sb_security(struct super_block *, struct dentry *, struct nfs_mount_info *);
struct dentry *nfs_fs_mount_common(struct nfs_server *, int, const char *,
				   struct nfs_mount_info *, struct nfs_subversion *);
struct dentry *nfs_fs_mount(struct file_system_type *, int, const char *, void *);
struct dentry * nfs_xdev_mount_common(struct file_system_type *, int,
		const char *, struct nfs_mount_info *);
void nfs_kill_super(struct super_block *);
void nfs_fill_super(struct super_block *, struct nfs_mount_info *);

extern struct rpc_stat nfs_rpcstat;

extern int __init register_nfs_fs(void);
extern void __exit unregister_nfs_fs(void);
extern void nfs_sb_active(struct super_block *sb);
extern void nfs_sb_deactive(struct super_block *sb);

/* namespace.c */
#define NFS_PATH_CANONICAL 1
extern char *nfs_path(char **p, struct dentry *dentry,
		      char *buffer, ssize_t buflen, unsigned flags);
extern struct vfsmount *nfs_d_automount(struct path *path);
struct vfsmount *nfs_submount(struct nfs_server *, struct dentry *,
			      struct nfs_fh *, struct nfs_fattr *);
struct vfsmount *nfs_do_submount(struct dentry *, struct nfs_fh *,
				 struct nfs_fattr *, rpc_authflavor_t);

/* getroot.c */
extern struct dentry *nfs_get_root(struct super_block *, struct nfs_fh *,
				   const char *);
#if IS_ENABLED(CONFIG_NFS_V4)
extern struct dentry *nfs4_get_root(struct super_block *, struct nfs_fh *,
				    const char *);

extern int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh, bool);
#endif

struct nfs_pgio_completion_ops;
/* read.c */
extern void nfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
			struct inode *inode, bool force_mds,
			const struct nfs_pgio_completion_ops *compl_ops);
extern void nfs_read_prepare(struct rpc_task *task, void *calldata);
extern void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio);

/* super.c */
void nfs_clone_super(struct super_block *, struct nfs_mount_info *);
void nfs_umount_begin(struct super_block *);
int  nfs_statfs(struct dentry *, struct kstatfs *);
int  nfs_show_options(struct seq_file *, struct dentry *);
int  nfs_show_devname(struct seq_file *, struct dentry *);
int  nfs_show_path(struct seq_file *, struct dentry *);
int  nfs_show_stats(struct seq_file *, struct dentry *);
void nfs_put_super(struct super_block *);
int nfs_remount(struct super_block *sb, int *flags, char *raw_data);

/* write.c */
extern void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
			struct inode *inode, int ioflags, bool force_mds,
			const struct nfs_pgio_completion_ops *compl_ops);
extern void nfs_pageio_reset_write_mds(struct nfs_pageio_descriptor *pgio);
extern void nfs_commit_free(struct nfs_commit_data *p);
extern void nfs_write_prepare(struct rpc_task *task, void *calldata);
extern void nfs_commit_prepare(struct rpc_task *task, void *calldata);
extern int nfs_initiate_commit(struct rpc_clnt *clnt,
			       struct nfs_commit_data *data,
			       const struct rpc_call_ops *call_ops,
			       int how, int flags);
extern void nfs_init_commit(struct nfs_commit_data *data,
			    struct list_head *head,
			    struct pnfs_layout_segment *lseg,
			    struct nfs_commit_info *cinfo);
int nfs_scan_commit_list(struct list_head *src, struct list_head *dst,
			 struct nfs_commit_info *cinfo, int max);
unsigned long nfs_reqs_to_commit(struct nfs_commit_info *);
int nfs_scan_commit(struct inode *inode, struct list_head *dst,
		    struct nfs_commit_info *cinfo);
void nfs_mark_request_commit(struct nfs_page *req,
			     struct pnfs_layout_segment *lseg,
			     struct nfs_commit_info *cinfo);
int nfs_generic_commit_list(struct inode *inode, struct list_head *head,
			    int how, struct nfs_commit_info *cinfo);
void nfs_retry_commit(struct list_head *page_list,
		      struct pnfs_layout_segment *lseg,
		      struct nfs_commit_info *cinfo);
void nfs_commitdata_release(struct nfs_commit_data *data);
void nfs_request_add_commit_list(struct nfs_page *req, struct list_head *dst,
				 struct nfs_commit_info *cinfo);
void nfs_request_remove_commit_list(struct nfs_page *req,
				    struct nfs_commit_info *cinfo);
void nfs_init_cinfo(struct nfs_commit_info *cinfo,
		    struct inode *inode,
		    struct nfs_direct_req *dreq);
int nfs_key_timeout_notify(struct file *filp, struct inode *inode);
bool nfs_ctx_key_to_expire(struct nfs_open_context *ctx);

#ifdef CONFIG_MIGRATION
extern int nfs_migrate_page(struct address_space *,
		struct page *, struct page *, enum migrate_mode);
#else
#define nfs_migrate_page NULL
#endif

/* unlink.c */
extern struct rpc_task *
nfs_async_rename(struct inode *old_dir, struct inode *new_dir,
		 struct dentry *old_dentry, struct dentry *new_dentry,
		 void (*complete)(struct rpc_task *, struct nfs_renamedata *));
extern int nfs_sillyrename(struct inode *dir, struct dentry *dentry);

/* direct.c */
void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
			      struct nfs_direct_req *dreq);
static inline void nfs_inode_dio_wait(struct inode *inode)
{
	inode_dio_wait(inode);
}
extern ssize_t nfs_dreq_bytes_left(struct nfs_direct_req *dreq);

/* nfs4proc.c */
extern void __nfs4_read_done_cb(struct nfs_pgio_data *);
extern struct nfs_client *nfs4_init_client(struct nfs_client *clp,
			    const struct rpc_timeout *timeparms,
			    const char *ip_addr);
extern int nfs40_walk_client_list(struct nfs_client *clp,
				struct nfs_client **result,
				struct rpc_cred *cred);
extern int nfs41_walk_client_list(struct nfs_client *clp,
				struct nfs_client **result,
				struct rpc_cred *cred);

/*
 * Determine the device name as a string
 */
static inline char *nfs_devname(struct dentry *dentry,
				char *buffer, ssize_t buflen)
{
	char *dummy;
	return nfs_path(&dummy, dentry, buffer, buflen, NFS_PATH_CANONICAL);
}

/*
 * Determine the actual block size (and log2 thereof)
 */
static inline
unsigned long nfs_block_bits(unsigned long bsize, unsigned char *nrbitsp)
{
	/* make sure blocksize is a power of two */
	if ((bsize & (bsize - 1)) || nrbitsp) {
		unsigned char	nrbits;

		for (nrbits = 31; nrbits && !(bsize & (1 << nrbits)); nrbits--)
			;
		bsize = 1 << nrbits;
		if (nrbitsp)
			*nrbitsp = nrbits;
	}

	return bsize;
}

/*
 * Calculate the number of 512byte blocks used.
 */
static inline blkcnt_t nfs_calc_block_size(u64 tsize)
{
	blkcnt_t used = (tsize + 511) >> 9;
	return (used > ULONG_MAX) ? ULONG_MAX : used;
}

/*
 * Compute and set NFS server blocksize
 */
static inline
unsigned long nfs_block_size(unsigned long bsize, unsigned char *nrbitsp)
{
	if (bsize < NFS_MIN_FILE_IO_SIZE)
		bsize = NFS_DEF_FILE_IO_SIZE;
	else if (bsize >= NFS_MAX_FILE_IO_SIZE)
		bsize = NFS_MAX_FILE_IO_SIZE;

	return nfs_block_bits(bsize, nrbitsp);
}

/*
 * Determine the maximum file size for a superblock
 */
static inline
void nfs_super_set_maxbytes(struct super_block *sb, __u64 maxfilesize)
{
	sb->s_maxbytes = (loff_t)maxfilesize;
	if (sb->s_maxbytes > MAX_LFS_FILESIZE || sb->s_maxbytes <= 0)
		sb->s_maxbytes = MAX_LFS_FILESIZE;
}

/*
 * Determine the number of bytes of data the page contains
 */
static inline
unsigned int nfs_page_length(struct page *page)
{
	loff_t i_size = i_size_read(page_file_mapping(page)->host);

	if (i_size > 0) {
		pgoff_t page_index = page_file_index(page);
		pgoff_t end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;
		if (page_index < end_index)
			return PAGE_CACHE_SIZE;
		if (page_index == end_index)
			return ((i_size - 1) & ~PAGE_CACHE_MASK) + 1;
	}
	return 0;
}

/*
 * Convert a umode to a dirent->d_type
 */
static inline
unsigned char nfs_umode_to_dtype(umode_t mode)
{
	return (mode >> 12) & 15;
}

/*
 * Determine the number of pages in an array of length 'len' and
 * with a base offset of 'base'
 */
static inline
unsigned int nfs_page_array_len(unsigned int base, size_t len)
{
	return ((unsigned long)len + (unsigned long)base +
		PAGE_SIZE - 1) >> PAGE_SHIFT;
}

/*
 * Convert a struct timespec into a 64-bit change attribute
 *
 * This does approximately the same thing as timespec_to_ns(),
 * but for calculation efficiency, we multiply the seconds by
 * 1024*1024*1024.
 */
static inline
u64 nfs_timespec_to_change_attr(const struct timespec *ts)
{
	return ((u64)ts->tv_sec << 30) + ts->tv_nsec;
}

#ifdef CONFIG_CRC32
/**
 * nfs_fhandle_hash - calculate the crc32 hash for the filehandle
 * @fh - pointer to filehandle
 *
 * returns a crc32 hash for the filehandle that is compatible with
 * the one displayed by "wireshark".
 */
static inline u32 nfs_fhandle_hash(const struct nfs_fh *fh)
{
	return ~crc32_le(0xFFFFFFFF, &fh->data[0], fh->size);
}
#else
static inline u32 nfs_fhandle_hash(const struct nfs_fh *fh)
{
	return 0;
}
#endif