alistair23-linux/include/linux/cleancache.h

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

#include <linux/fs.h>
#include <linux/exportfs.h>
#include <linux/mm.h>

#define CLEANCACHE_NO_POOL		-1
#define CLEANCACHE_NO_BACKEND		-2
#define CLEANCACHE_NO_BACKEND_SHARED	-3

#define CLEANCACHE_KEY_MAX 6

/*
 * cleancache requires every file with a page in cleancache to have a
 * unique key unless/until the file is removed/truncated.  For some
 * filesystems, the inode number is unique, but for "modern" filesystems
 * an exportable filehandle is required (see exportfs.h)
 */
struct cleancache_filekey {
	union {
		ino_t ino;
		__u32 fh[CLEANCACHE_KEY_MAX];
		u32 key[CLEANCACHE_KEY_MAX];
	} u;
};

struct cleancache_ops {
	int (*init_fs)(size_t);
	int (*init_shared_fs)(uuid_t *uuid, size_t);
	int (*get_page)(int, struct cleancache_filekey,
			pgoff_t, struct page *);
	void (*put_page)(int, struct cleancache_filekey,
			pgoff_t, struct page *);
	void (*invalidate_page)(int, struct cleancache_filekey, pgoff_t);
	void (*invalidate_inode)(int, struct cleancache_filekey);
	void (*invalidate_fs)(int);
};

extern int cleancache_register_ops(const struct cleancache_ops *ops);
extern void __cleancache_init_fs(struct super_block *);
extern void __cleancache_init_shared_fs(struct super_block *);
extern int  __cleancache_get_page(struct page *);
extern void __cleancache_put_page(struct page *);
extern void __cleancache_invalidate_page(struct address_space *, struct page *);
extern void __cleancache_invalidate_inode(struct address_space *);
extern void __cleancache_invalidate_fs(struct super_block *);

#ifdef CONFIG_CLEANCACHE
#define cleancache_enabled (1)
static inline bool cleancache_fs_enabled_mapping(struct address_space *mapping)
{
	return mapping->host->i_sb->cleancache_poolid >= 0;
}
static inline bool cleancache_fs_enabled(struct page *page)
{
	return cleancache_fs_enabled_mapping(page->mapping);
}
#else
#define cleancache_enabled (0)
#define cleancache_fs_enabled(_page) (0)
#define cleancache_fs_enabled_mapping(_page) (0)
#endif

/*
 * The shim layer provided by these inline functions allows the compiler
 * to reduce all cleancache hooks to nothingness if CONFIG_CLEANCACHE
 * is disabled, to a single global variable check if CONFIG_CLEANCACHE
 * is enabled but no cleancache "backend" has dynamically enabled it,
 * and, for the most frequent cleancache ops, to a single global variable
 * check plus a superblock element comparison if CONFIG_CLEANCACHE is enabled
 * and a cleancache backend has dynamically enabled cleancache, but the
 * filesystem referenced by that cleancache op has not enabled cleancache.
 * As a result, CONFIG_CLEANCACHE can be enabled by default with essentially
 * no measurable performance impact.
 */

static inline void cleancache_init_fs(struct super_block *sb)
{
	if (cleancache_enabled)
		__cleancache_init_fs(sb);
}

static inline void cleancache_init_shared_fs(struct super_block *sb)
{
	if (cleancache_enabled)
		__cleancache_init_shared_fs(sb);
}

static inline int cleancache_get_page(struct page *page)
{
	if (cleancache_enabled && cleancache_fs_enabled(page))
		return __cleancache_get_page(page);
	return -1;
}

static inline void cleancache_put_page(struct page *page)
{
	if (cleancache_enabled && cleancache_fs_enabled(page))
		__cleancache_put_page(page);
}

static inline void cleancache_invalidate_page(struct address_space *mapping,
					struct page *page)
{
	/* careful... page->mapping is NULL sometimes when this is called */
	if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
		__cleancache_invalidate_page(mapping, page);
}

static inline void cleancache_invalidate_inode(struct address_space *mapping)
{
	if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
		__cleancache_invalidate_inode(mapping);
}

static inline void cleancache_invalidate_fs(struct super_block *sb)
{
	if (cleancache_enabled)
		__cleancache_invalidate_fs(sb);
}

#endif /* _LINUX_CLEANCACHE_H */