/* 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 ([email protected])
 *
 * 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>
#include <linux/uio.h>

enum netfs_sreq_ref_trace;

/*
 * 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 folio_test_fscache(folio)    folio_test_private_2(folio)
#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))

/**
 * folio_start_fscache - Start an fscache write on a folio.
 * @folio: The folio.
 *
 * Call this function before writing a folio to a local cache.  Starting a
 * second write before the first one finishes is not allowed.
 */
static inline void folio_start_fscache(struct folio *folio)
{
    VM_BUG_ON_FOLIO(folio_test_private_2(folio), folio);
    folio_get(folio);
    folio_set_private_2(folio);
}

/**
 * folio_end_fscache - End an fscache write on a folio.
 * @folio: The folio.
 *
 * Call this function after the folio has been written to the local cache.
 * This will wake any sleepers waiting on this folio.
 */
static inline void folio_end_fscache(struct folio *folio)
{
    folio_end_private_2(folio);
}

/**
 * folio_wait_fscache - Wait for an fscache write on this folio to end.
 * @folio: The folio.
 *
 * If this folio is currently being written to a local cache, wait for
 * the write to finish.  Another write may start after this one finishes,
 * unless the caller holds the folio lock.
 */
static inline void folio_wait_fscache(struct folio *folio)
{
    folio_wait_private_2(folio);
}

/**
 * folio_wait_fscache_killable - Wait for an fscache write on this folio to end.
 * @folio: The folio.
 *
 * If this folio is currently being written to a local cache, wait
 * for the write to finish or for a fatal signal to be received.
 * Another write may start after this one finishes, unless the caller
 * holds the folio lock.
 *
 * Return:
 * - 0 if successful.
 * - -EINTR if a fatal signal was encountered.
 */
static inline int folio_wait_fscache_killable(struct folio *folio)
{
    return folio_wait_private_2_killable(folio);
}

static inline void set_page_fscache(struct page *page)
{
    folio_start_fscache(page_folio(page));
}

static inline void end_page_fscache(struct page *page)
{
    folio_end_private_2(page_folio(page));
}

static inline void wait_on_page_fscache(struct page *page)
{
    folio_wait_private_2(page_folio(page));
}

static inline int wait_on_page_fscache_killable(struct page *page)
{
    return folio_wait_private_2_killable(page_folio(page));
}

enum netfs_io_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);

/*
 * Per-inode context.  This wraps the VFS inode.
 */
struct netfs_inode {
    struct inode        inode;        /* The VFS inode */
    const struct netfs_request_ops *ops;
#if IS_ENABLED(CONFIG_FSCACHE)
    struct fscache_cookie    *cache;
#endif
    loff_t            remote_i_size;    /* Size of the remote file */
};

/*
 * 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 */
    unsigned int            inval_counter;    /* object->inval_counter at begin_op */
};

/*
 * Descriptor for a single component subrequest.
 */
struct netfs_io_subrequest {
    struct netfs_io_request *rreq;        /* Supervising I/O 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        ref;
    short            error;        /* 0 or error that occurred */
    unsigned short        debug_index;    /* Index in list (for debugging output) */
    enum netfs_io_source    source;        /* Where to read from/write to */
    unsigned long        flags;
#define NETFS_SREQ_COPY_TO_CACHE    0    /* Set if should copy the data to the cache */
#define NETFS_SREQ_CLEAR_TAIL        1    /* Set if the rest of the read should be cleared */
#define NETFS_SREQ_SHORT_IO        2    /* Set if the I/O was short */
#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 */
#define NETFS_SREQ_ONDEMAND        5    /* Set if it's from on-demand read mode */
};

enum netfs_io_origin {
    NETFS_READAHEAD,        /* This read was triggered by readahead */
    NETFS_READPAGE,            /* This read is a synchronous read */
    NETFS_READ_FOR_WRITE,        /* This read is to prepare a write */
} __mode(byte);

/*
 * Descriptor for an I/O helper request.  This is used to make multiple I/O
 * operations to a variety of data stores and then stitch the result together.
 */
struct netfs_io_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;    /* Contributory I/O operations */
    void            *netfs_priv;    /* Private data for the netfs */
    unsigned int        debug_id;
    atomic_t        nr_outstanding;    /* Number of ops in progress */
    atomic_t        nr_copy_ops;    /* Number of copy-to-cache 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 */
    enum netfs_io_origin    origin;        /* Origin of the request */
    loff_t            i_size;        /* Size of the file */
    loff_t            start;        /* Start position */
    pgoff_t            no_unlock_folio; /* Don't unlock this folio after read */
    refcount_t        ref;
    unsigned long        flags;
#define NETFS_RREQ_INCOMPLETE_IO    0    /* Some ioreqs terminated short or with error */
#define NETFS_RREQ_COPY_TO_CACHE    1    /* Need to write to the cache */
#define NETFS_RREQ_NO_UNLOCK_FOLIO    2    /* Don't unlock no_unlock_folio on completion */
#define NETFS_RREQ_DONT_UNLOCK_FOLIOS    3    /* Don't unlock the folios on completion */
#define NETFS_RREQ_FAILED        4    /* The request failed */
#define NETFS_RREQ_IN_PROGRESS        5    /* Unlocked when the request completes */
    const struct netfs_request_ops *netfs_ops;
};

/*
 * Operations the network filesystem can/must provide to the helpers.
 */
struct netfs_request_ops {
    int (*init_request)(struct netfs_io_request *rreq, struct file *file);
    void (*free_request)(struct netfs_io_request *rreq);
    int (*begin_cache_operation)(struct netfs_io_request *rreq);

    void (*expand_readahead)(struct netfs_io_request *rreq);
    bool (*clamp_length)(struct netfs_io_subrequest *subreq);
    void (*issue_read)(struct netfs_io_subrequest *subreq);
    bool (*is_still_valid)(struct netfs_io_request *rreq);
    int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
                 struct folio **foliop, void **_fsdata);
    void (*done)(struct netfs_io_request *rreq);
};

/*
 * How to handle reading from a hole.
 */
enum netfs_read_from_hole {
    NETFS_READ_HOLE_IGNORE,
    NETFS_READ_HOLE_CLEAR,
    NETFS_READ_HOLE_FAIL,
};

/*
 * 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,
            enum netfs_read_from_hole read_hole,
            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_io_source (*prepare_read)(struct netfs_io_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,
                 bool no_space_allocated_yet);

    /* Prepare an on-demand read operation, shortening it to a cached/uncached
     * boundary as appropriate.
     */
    enum netfs_io_source (*prepare_ondemand_read)(struct netfs_cache_resources *cres,
                              loff_t start, size_t *_len,
                              loff_t i_size,
                              unsigned long *_flags, ino_t ino);

    /* Query the occupancy of the cache in a region, returning where the
     * next chunk of data starts and how long it is.
     */
    int (*query_occupancy)(struct netfs_cache_resources *cres,
                   loff_t start, size_t len, size_t granularity,
                   loff_t *_data_start, size_t *_data_len);
};

struct readahead_control;
void netfs_readahead(struct readahead_control *);
int netfs_read_folio(struct file *, struct folio *);
int netfs_write_begin(struct netfs_inode *, struct file *,
        struct address_space *, loff_t pos, unsigned int len,
        struct folio **, void **fsdata);

void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
              enum netfs_sreq_ref_trace what);
void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
              bool was_async, enum netfs_sreq_ref_trace what);
void netfs_stats_show(struct seq_file *);
ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len,
                struct iov_iter *new,
                iov_iter_extraction_t extraction_flags);

/**
 * netfs_inode - Get the netfs inode context from the inode
 * @inode: The inode to query
 *
 * Get the netfs lib inode context from the network filesystem's inode.  The
 * context struct is expected to directly follow on from the VFS inode struct.
 */
static inline struct netfs_inode *netfs_inode(struct inode *inode)
{
    return container_of(inode, struct netfs_inode, inode);
}

/**
 * netfs_inode_init - Initialise a netfslib inode context
 * @ctx: The netfs inode to initialise
 * @ops: The netfs's operations list
 *
 * Initialise the netfs library context struct.  This is expected to follow on
 * directly from the VFS inode struct.
 */
static inline void netfs_inode_init(struct netfs_inode *ctx,
                    const struct netfs_request_ops *ops)
{
    ctx->ops = ops;
    ctx->remote_i_size = i_size_read(&ctx->inode);
#if IS_ENABLED(CONFIG_FSCACHE)
    ctx->cache = NULL;
#endif
}

/**
 * netfs_resize_file - Note that a file got resized
 * @ctx: The netfs inode being resized
 * @new_i_size: The new file size
 *
 * Inform the netfs lib that a file got resized so that it can adjust its state.
 */
static inline void netfs_resize_file(struct netfs_inode *ctx, loff_t new_i_size)
{
    ctx->remote_i_size = new_i_size;
}

/**
 * netfs_i_cookie - Get the cache cookie from the inode
 * @ctx: The netfs inode to query
 *
 * Get the caching cookie (if enabled) from the network filesystem's inode.
 */
static inline struct fscache_cookie *netfs_i_cookie(struct netfs_inode *ctx)
{
#if IS_ENABLED(CONFIG_FSCACHE)
    return ctx->cache;
#else
    return NULL;
#endif
}

#endif /* _LINUX_NETFS_H */