linux-mainline/include/linux/exportfs.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef LINUX_EXPORTFS_H
#define LINUX_EXPORTFS_H 1

#include <linux/types.h>
#include <linux/path.h>

struct dentry;
struct iattr;
struct inode;
struct iomap;
struct super_block;
struct vfsmount;

/* limit the handle size to NFSv4 handle size now */
#define MAX_HANDLE_SZ 128

/*
 * The fileid_type identifies how the file within the filesystem is encoded.
 * In theory this is freely set and parsed by the filesystem, but we try to
 * stick to conventions so we can share some generic code and don't confuse
 * sniffers like ethereal/wireshark.
 *
 * The filesystem must not use the value '0' or '0xff'.
 */
enum fid_type {
	/*
	 * The root, or export point, of the filesystem.
	 * (Never actually passed down to the filesystem.
	 */
	FILEID_ROOT = 0,

	/*
	 * 32bit inode number, 32 bit generation number.
	 */
	FILEID_INO32_GEN = 1,

	/*
	 * 32bit inode number, 32 bit generation number,
	 * 32 bit parent directory inode number.
	 */
	FILEID_INO32_GEN_PARENT = 2,

	/*
	 * 64 bit object ID, 64 bit root object ID,
	 * 32 bit generation number.
	 */
	FILEID_BTRFS_WITHOUT_PARENT = 0x4d,

	/*
	 * 64 bit object ID, 64 bit root object ID,
	 * 32 bit generation number,
	 * 64 bit parent object ID, 32 bit parent generation.
	 */
	FILEID_BTRFS_WITH_PARENT = 0x4e,

	/*
	 * 64 bit object ID, 64 bit root object ID,
	 * 32 bit generation number,
	 * 64 bit parent object ID, 32 bit parent generation,
	 * 64 bit parent root object ID.
	 */
	FILEID_BTRFS_WITH_PARENT_ROOT = 0x4f,

	/*
	 * 32 bit block number, 16 bit partition reference,
	 * 16 bit unused, 32 bit generation number.
	 */
	FILEID_UDF_WITHOUT_PARENT = 0x51,

	/*
	 * 32 bit block number, 16 bit partition reference,
	 * 16 bit unused, 32 bit generation number,
	 * 32 bit parent block number, 32 bit parent generation number
	 */
	FILEID_UDF_WITH_PARENT = 0x52,

	/*
	 * 64 bit checkpoint number, 64 bit inode number,
	 * 32 bit generation number.
	 */
	FILEID_NILFS_WITHOUT_PARENT = 0x61,

	/*
	 * 64 bit checkpoint number, 64 bit inode number,
	 * 32 bit generation number, 32 bit parent generation.
	 * 64 bit parent inode number.
	 */
	FILEID_NILFS_WITH_PARENT = 0x62,

	/*
	 * 32 bit generation number, 40 bit i_pos.
	 */
	FILEID_FAT_WITHOUT_PARENT = 0x71,

	/*
	 * 32 bit generation number, 40 bit i_pos,
	 * 32 bit parent generation number, 40 bit parent i_pos
	 */
	FILEID_FAT_WITH_PARENT = 0x72,

	/*
	 * 64 bit inode number, 32 bit generation number.
	 */
	FILEID_INO64_GEN = 0x81,

	/*
	 * 64 bit inode number, 32 bit generation number,
	 * 64 bit parent inode number, 32 bit parent generation.
	 */
	FILEID_INO64_GEN_PARENT = 0x82,

	/*
	 * 128 bit child FID (struct lu_fid)
	 * 128 bit parent FID (struct lu_fid)
	 */
	FILEID_LUSTRE = 0x97,

	/*
	 * 64 bit inode number, 32 bit subvolume, 32 bit generation number:
	 */
	FILEID_BCACHEFS_WITHOUT_PARENT = 0xb1,
	FILEID_BCACHEFS_WITH_PARENT = 0xb2,

	/*
	 * 64 bit unique kernfs id
	 */
	FILEID_KERNFS = 0xfe,

	/*
	 * Filesystems must not use 0xff file ID.
	 */
	FILEID_INVALID = 0xff,
};

struct fid {
	union {
		struct {
			u32 ino;
			u32 gen;
			u32 parent_ino;
			u32 parent_gen;
		} i32;
		struct {
			u64 ino;
			u32 gen;
		} __packed i64;
		struct {
 			u32 block;
 			u16 partref;
 			u16 parent_partref;
 			u32 generation;
 			u32 parent_block;
 			u32 parent_generation;
 		} udf;
		DECLARE_FLEX_ARRAY(__u32, raw);
	};
};

enum handle_to_path_flags {
	HANDLE_CHECK_PERMS   = (1 << 0),
	HANDLE_CHECK_SUBTREE = (1 << 1),
};

struct handle_to_path_ctx {
	struct path root;
	enum handle_to_path_flags flags;
	unsigned int fh_flags;
};

#define EXPORT_FH_CONNECTABLE	0x1 /* Encode file handle with parent */
#define EXPORT_FH_FID		0x2 /* File handle may be non-decodeable */
#define EXPORT_FH_DIR_ONLY	0x4 /* Only decode file handle for a directory */

/*
 * Filesystems use only lower 8 bits of file_handle type for fid_type.
 * name_to_handle_at() uses upper 16 bits of type as user flags to be
 * interpreted by open_by_handle_at().
 */
#define FILEID_USER_FLAGS_MASK	0xffff0000
#define FILEID_USER_FLAGS(type) ((type) & FILEID_USER_FLAGS_MASK)

/* Flags supported in encoded handle_type that is exported to user */
#define FILEID_IS_CONNECTABLE	0x10000
#define FILEID_IS_DIR		0x20000
#define FILEID_VALID_USER_FLAGS	(FILEID_IS_CONNECTABLE | FILEID_IS_DIR)

/**
 * struct export_operations - for nfsd to communicate with file systems
 * @encode_fh:      encode a file handle fragment from a dentry
 * @fh_to_dentry:   find the implied object and get a dentry for it
 * @fh_to_parent:   find the implied object's parent and get a dentry for it
 * @get_name:       find the name for a given inode in a given directory
 * @get_parent:     find the parent of a given directory
 * @commit_metadata: commit metadata changes to stable storage
 *
 * See Documentation/filesystems/nfs/exporting.rst for details on how to use
 * this interface correctly.
 *
 * encode_fh:
 *    @encode_fh should store in the file handle fragment @fh (using at most
 *    @max_len bytes) information that can be used by @decode_fh to recover the
 *    file referred to by the &struct dentry @de.  If @flag has CONNECTABLE bit
 *    set, the encode_fh() should store sufficient information so that a good
 *    attempt can be made to find not only the file but also it's place in the
 *    filesystem.   This typically means storing a reference to de->d_parent in
 *    the filehandle fragment.  encode_fh() should return the fileid_type on
 *    success and on error returns 255 (if the space needed to encode fh is
 *    greater than @max_len*4 bytes). On error @max_len contains the minimum
 *    size(in 4 byte unit) needed to encode the file handle.
 *
 * fh_to_dentry:
 *    @fh_to_dentry is given a &struct super_block (@sb) and a file handle
 *    fragment (@fh, @fh_len). It should return a &struct dentry which refers
 *    to the same file that the file handle fragment refers to.  If it cannot,
 *    it should return a %NULL pointer if the file cannot be found, or an
 *    %ERR_PTR error code of %ENOMEM if a memory allocation failure occurred.
 *    Any other error code is treated like %NULL, and will cause an %ESTALE error
 *    for callers of exportfs_decode_fh().
 *    Any suitable dentry can be returned including, if necessary, a new dentry
 *    created with d_alloc_root.  The caller can then find any other extant
 *    dentries by following the d_alias links.
 *
 * fh_to_parent:
 *    Same as @fh_to_dentry, except that it returns a pointer to the parent
 *    dentry if it was encoded into the filehandle fragment by @encode_fh.
 *
 * get_name:
 *    @get_name should find a name for the given @child in the given @parent
 *    directory.  The name should be stored in the @name (with the
 *    understanding that it is already pointing to a %NAME_MAX+1 sized
 *    buffer.   get_name() should return %0 on success, a negative error code
 *    or error.  @get_name will be called without @parent->i_mutex held.
 *
 * get_parent:
 *    @get_parent should find the parent directory for the given @child which
 *    is also a directory.  In the event that it cannot be found, or storage
 *    space cannot be allocated, a %ERR_PTR should be returned.
 *
 * permission:
 *    Allow filesystems to specify a custom permission function.
 *
 * open:
 *    Allow filesystems to specify a custom open function.
 *
 * commit_metadata:
 *    @commit_metadata should commit metadata changes to stable storage.
 *
 * Locking rules:
 *    get_parent is called with child->d_inode->i_mutex down
 *    get_name is not (which is possibly inconsistent)
 */

struct export_operations {
	int (*encode_fh)(struct inode *inode, __u32 *fh, int *max_len,
			struct inode *parent);
	struct dentry * (*fh_to_dentry)(struct super_block *sb, struct fid *fid,
			int fh_len, int fh_type);
	struct dentry * (*fh_to_parent)(struct super_block *sb, struct fid *fid,
			int fh_len, int fh_type);
	int (*get_name)(struct dentry *parent, char *name,
			struct dentry *child);
	struct dentry * (*get_parent)(struct dentry *child);
	int (*commit_metadata)(struct inode *inode);

	int (*get_uuid)(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
	int (*map_blocks)(struct inode *inode, loff_t offset,
			  u64 len, struct iomap *iomap,
			  bool write, u32 *device_generation);
	int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
			     int nr_iomaps, struct iattr *iattr);
	int (*permission)(struct handle_to_path_ctx *ctx, unsigned int oflags);
	struct file * (*open)(struct path *path, unsigned int oflags);
#define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
#define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
#define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */
#define EXPORT_OP_REMOTE_FS		(0x8) /* Filesystem is remote */
#define EXPORT_OP_NOATOMIC_ATTR		(0x10) /* Filesystem cannot supply
						  atomic attribute updates
						*/
#define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
#define EXPORT_OP_NOLOCKS		(0x40) /* no file locking support */
	unsigned long	flags;
};

/**
 * exportfs_cannot_lock() - check if export implements file locking
 * @export_ops:	the nfs export operations to check
 *
 * Returns true if the export does not support file locking.
 */
static inline bool
exportfs_cannot_lock(const struct export_operations *export_ops)
{
	return export_ops->flags & EXPORT_OP_NOLOCKS;
}

extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
				    int *max_len, struct inode *parent,
				    int flags);
extern int exportfs_encode_fh(struct dentry *dentry, struct fid *fid,
			      int *max_len, int flags);

static inline bool exportfs_can_encode_fid(const struct export_operations *nop)
{
	return !nop || nop->encode_fh;
}

static inline bool exportfs_can_decode_fh(const struct export_operations *nop)
{
	return nop && nop->fh_to_dentry;
}

static inline bool exportfs_can_encode_fh(const struct export_operations *nop,
					  int fh_flags)
{
	/*
	 * If a non-decodeable file handle was requested, we only need to make
	 * sure that filesystem did not opt-out of encoding fid.
	 */
	if (fh_flags & EXPORT_FH_FID)
		return exportfs_can_encode_fid(nop);

	/*
	 * If a decodeable file handle was requested, we need to make sure that
	 * filesystem can also decode file handles.
	 */
	return exportfs_can_decode_fh(nop);
}

static inline int exportfs_encode_fid(struct inode *inode, struct fid *fid,
				      int *max_len)
{
	return exportfs_encode_inode_fh(inode, fid, max_len, NULL,
					EXPORT_FH_FID);
}

extern struct dentry *exportfs_decode_fh_raw(struct vfsmount *mnt,
					     struct fid *fid, int fh_len,
					     int fileid_type,
					     unsigned int flags,
					     int (*acceptable)(void *, struct dentry *),
					     void *context);
extern struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
	int fh_len, int fileid_type, int (*acceptable)(void *, struct dentry *),
	void *context);

/*
 * Generic helpers for filesystems.
 */
int generic_encode_ino32_fh(struct inode *inode, __u32 *fh, int *max_len,
			    struct inode *parent);
struct dentry *generic_fh_to_dentry(struct super_block *sb,
	struct fid *fid, int fh_len, int fh_type,
	struct inode *(*get_inode) (struct super_block *sb, u64 ino, u32 gen));
struct dentry *generic_fh_to_parent(struct super_block *sb,
	struct fid *fid, int fh_len, int fh_type,
	struct inode *(*get_inode) (struct super_block *sb, u64 ino, u32 gen));

#endif /* LINUX_EXPORTFS_H */