/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Network filesystem support services.
 *
 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * See:
 *
 *      Documentation/filesystems/netfs_library.rst
 *
 * for a description of the network filesystem interface declared here.
 */

#ifndef _LINUX_NETFS_H
#define _LINUX_NETFS_H

#include <linux/workqueue.h>
#include <linux/fs.h>
#include <linux/pagemap.h>

/*
 * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
 * a page is currently backed by a local disk cache
 */
#define PageFsCache(page)               PagePrivate2((page))
#define SetPageFsCache(page)            SetPagePrivate2((page))
#define ClearPageFsCache(page)          ClearPagePrivate2((page))
#define TestSetPageFsCache(page)        TestSetPagePrivate2((page))
#define TestClearPageFsCache(page)      TestClearPagePrivate2((page))

/**
 * set_page_fscache - Set PG_fscache on a page and take a ref
 * @page: The page.
 *
 * Set the PG_fscache (PG_private_2) flag on a page and take the reference
 * needed for the VM to handle its lifetime correctly.  This sets the flag and
 * takes the reference unconditionally, so care must be taken not to set the
 * flag again if it's already set.
 */
static inline void set_page_fscache(struct page *page)
{
        set_page_private_2(page);
}

/**
 * end_page_fscache - Clear PG_fscache and release any waiters
 * @page: The page
 *
 * Clear the PG_fscache (PG_private_2) bit on a page and wake up any sleepers
 * waiting for this.  The page ref held for PG_private_2 being set is released.
 *
 * This is, for example, used when a netfs page is being written to a local
 * disk cache, thereby allowing writes to the cache for the same page to be
 * serialised.
 */
static inline void end_page_fscache(struct page *page)
{
        end_page_private_2(page);
}

/**
 * wait_on_page_fscache - Wait for PG_fscache to be cleared on a page
 * @page: The page to wait on
 *
 * Wait for PG_fscache (aka PG_private_2) to be cleared on a page.
 */
static inline void wait_on_page_fscache(struct page *page)
{
        wait_on_page_private_2(page);
}

/**
 * wait_on_page_fscache_killable - Wait for PG_fscache to be cleared on a page
 * @page: The page to wait on
 *
 * Wait for PG_fscache (aka PG_private_2) to be cleared on a page or until a
 * fatal signal is received by the calling task.
 *
 * Return:
 * - 0 if successful.
 * - -EINTR if a fatal signal was encountered.
 */
static inline int wait_on_page_fscache_killable(struct page *page)
{
        return wait_on_page_private_2_killable(page);
}

enum netfs_read_source {
        NETFS_FILL_WITH_ZEROES,
        NETFS_DOWNLOAD_FROM_SERVER,
        NETFS_READ_FROM_CACHE,
        NETFS_INVALID_READ,
} __mode(byte);

typedef void (*netfs_io_terminated_t)(void *priv, ssize_t transferred_or_error,
                                      bool was_async);

/*
 * Resources required to do operations on a cache.
 */
struct netfs_cache_resources {
        const struct netfs_cache_ops    *ops;
        void                            *cache_priv;
        void                            *cache_priv2;
        unsigned int                    debug_id;       /* Cookie debug ID */
};

/*
 * Descriptor for a single component subrequest.
 */
struct netfs_read_subrequest {
        struct netfs_read_request *rreq;        /* Supervising read request */
        struct list_head        rreq_link;      /* Link in rreq->subrequests */
        loff_t                  start;          /* Where to start the I/O */
        size_t                  len;            /* Size of the I/O */
        size_t                  transferred;    /* Amount of data transferred */
        refcount_t              usage;
        short                   error;          /* 0 or error that occurred */
        unsigned short          debug_index;    /* Index in list (for debugging output) */
        enum netfs_read_source  source;         /* Where to read from */
        unsigned long           flags;
#define NETFS_SREQ_WRITE_TO_CACHE       0       /* Set if should write to cache */
#define NETFS_SREQ_CLEAR_TAIL           1       /* Set if the rest of the read should be cleared */
#define NETFS_SREQ_SHORT_READ           2       /* Set if there was a short read from the cache */
#define NETFS_SREQ_SEEK_DATA_READ       3       /* Set if ->read() should SEEK_DATA first */
#define NETFS_SREQ_NO_PROGRESS          4       /* Set if we didn't manage to read any data */
};

/*
 * Descriptor for a read helper request.  This is used to make multiple I/O
 * requests on a variety of sources and then stitch the result together.
 */
struct netfs_read_request {
        struct work_struct      work;
        struct inode            *inode;         /* The file being accessed */
        struct address_space    *mapping;       /* The mapping being accessed */
        struct netfs_cache_resources cache_resources;
        struct list_head        subrequests;    /* Requests to fetch I/O from disk or net */
        void                    *netfs_priv;    /* Private data for the netfs */
        unsigned int            debug_id;
        atomic_t                nr_rd_ops;      /* Number of read ops in progress */
        atomic_t                nr_wr_ops;      /* Number of write ops in progress */
        size_t                  submitted;      /* Amount submitted for I/O so far */
        size_t                  len;            /* Length of the request */
        short                   error;          /* 0 or error that occurred */
        loff_t                  i_size;         /* Size of the file */
        loff_t                  start;          /* Start position */
        pgoff_t                 no_unlock_page; /* Don't unlock this page after read */
        refcount_t              usage;
        unsigned long           flags;
#define NETFS_RREQ_INCOMPLETE_IO        0       /* Some ioreqs terminated short or with error */
#define NETFS_RREQ_WRITE_TO_CACHE       1       /* Need to write to the cache */
#define NETFS_RREQ_NO_UNLOCK_PAGE       2       /* Don't unlock no_unlock_page on completion */
#define NETFS_RREQ_DONT_UNLOCK_PAGES    3       /* Don't unlock the pages on completion */
#define NETFS_RREQ_FAILED               4       /* The request failed */
#define NETFS_RREQ_IN_PROGRESS          5       /* Unlocked when the request completes */
        const struct netfs_read_request_ops *netfs_ops;
};

/*
 * Operations the network filesystem can/must provide to the helpers.
 */
struct netfs_read_request_ops {
        bool (*is_cache_enabled)(struct inode *inode);
        void (*init_rreq)(struct netfs_read_request *rreq, struct file *file);
        int (*begin_cache_operation)(struct netfs_read_request *rreq);
        void (*expand_readahead)(struct netfs_read_request *rreq);
        bool (*clamp_length)(struct netfs_read_subrequest *subreq);
        void (*issue_op)(struct netfs_read_subrequest *subreq);
        bool (*is_still_valid)(struct netfs_read_request *rreq);
        int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
                                 struct page *page, void **_fsdata);
        void (*done)(struct netfs_read_request *rreq);
        void (*cleanup)(struct address_space *mapping, void *netfs_priv);
};

/*
 * Table of operations for access to a cache.  This is obtained by
 * rreq->ops->begin_cache_operation().
 */
struct netfs_cache_ops {
        /* End an operation */
        void (*end_operation)(struct netfs_cache_resources *cres);

        /* Read data from the cache */
        int (*read)(struct netfs_cache_resources *cres,
                    loff_t start_pos,
                    struct iov_iter *iter,
                    bool seek_data,
                    netfs_io_terminated_t term_func,
                    void *term_func_priv);

        /* Write data to the cache */
        int (*write)(struct netfs_cache_resources *cres,
                     loff_t start_pos,
                     struct iov_iter *iter,
                     netfs_io_terminated_t term_func,
                     void *term_func_priv);

        /* Expand readahead request */
        void (*expand_readahead)(struct netfs_cache_resources *cres,
                                 loff_t *_start, size_t *_len, loff_t i_size);

        /* Prepare a read operation, shortening it to a cached/uncached
         * boundary as appropriate.
         */
        enum netfs_read_source (*prepare_read)(struct netfs_read_subrequest *subreq,
                                               loff_t i_size);

        /* Prepare a write operation, working out what part of the write we can
         * actually do.
         */
        int (*prepare_write)(struct netfs_cache_resources *cres,
                             loff_t *_start, size_t *_len, loff_t i_size);
};

struct readahead_control;
extern void netfs_readahead(struct readahead_control *,
                            const struct netfs_read_request_ops *,
                            void *);
extern int netfs_readpage(struct file *,
                          struct page *,
                          const struct netfs_read_request_ops *,
                          void *);
extern int netfs_write_begin(struct file *, struct address_space *,
                             loff_t, unsigned int, unsigned int, struct page **,
                             void **,
                             const struct netfs_read_request_ops *,
                             void *);

extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t, bool);
extern void netfs_stats_show(struct seq_file *);

#endif /* _LINUX_NETFS_H */