// SPDX-License-Identifier: GPL-2.0-or-later
/* kiocb-using read/write
 *
 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include <linux/falloc.h>
#include <linux/sched/mm.h>
#include <trace/events/fscache.h>
#include <trace/events/netfs.h>
#include "internal.h"

struct cachefiles_kiocb {
        struct kiocb            iocb;
        refcount_t              ki_refcnt;
        loff_t                  start;
        union {
                size_t          skipped;
                size_t          len;
        };
        struct cachefiles_object *object;
        netfs_io_terminated_t   term_func;
        void                    *term_func_priv;
        bool                    was_async;
        unsigned int            inval_counter;  /* Copy of cookie->inval_counter */
        u64                     b_writing;
};

static inline void cachefiles_put_kiocb(struct cachefiles_kiocb *ki)
{
        if (refcount_dec_and_test(&ki->ki_refcnt)) {
                cachefiles_put_object(ki->object, cachefiles_obj_put_ioreq);
                fput(ki->iocb.ki_filp);
                kfree(ki);
        }
}

/*
 * Handle completion of a read from the cache.
 */
static void cachefiles_read_complete(struct kiocb *iocb, long ret)
{
        struct cachefiles_kiocb *ki = container_of(iocb, struct cachefiles_kiocb, iocb);
        struct inode *inode = file_inode(ki->iocb.ki_filp);

        _enter("%ld", ret);

        if (ret < 0)
                trace_cachefiles_io_error(ki->object, inode, ret,
                                          cachefiles_trace_read_error);

        if (ki->term_func) {
                if (ret >= 0) {
                        if (ki->object->cookie->inval_counter == ki->inval_counter)
                                ki->skipped += ret;
                        else
                                ret = -ESTALE;
                }

                ki->term_func(ki->term_func_priv, ret);
        }

        cachefiles_put_kiocb(ki);
}

/*
 * Initiate a read from the cache.
 */
static int cachefiles_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)
{
        struct cachefiles_object *object;
        struct cachefiles_kiocb *ki;
        struct file *file;
        unsigned int old_nofs;
        ssize_t ret = -ENOBUFS;
        size_t len = iov_iter_count(iter), skipped = 0;

        if (!fscache_wait_for_operation(cres, FSCACHE_WANT_READ))
                goto presubmission_error;

        fscache_count_read();
        object = cachefiles_cres_object(cres);
        file = cachefiles_cres_file(cres);

        _enter("%pD,%li,%llx,%zx/%llx",
               file, file_inode(file)->i_ino, start_pos, len,
               i_size_read(file_inode(file)));

        /* If the caller asked us to seek for data before doing the read, then
         * we should do that now.  If we find a gap, we fill it with zeros.
         */
        if (read_hole != NETFS_READ_HOLE_IGNORE) {
                loff_t off = start_pos, off2;

                off2 = cachefiles_inject_read_error();
                if (off2 == 0)
                        off2 = vfs_llseek(file, off, SEEK_DATA);
                if (off2 < 0 && off2 >= (loff_t)-MAX_ERRNO && off2 != -ENXIO) {
                        skipped = 0;
                        ret = off2;
                        goto presubmission_error;
                }

                if (off2 == -ENXIO || off2 >= start_pos + len) {
                        /* The region is beyond the EOF or there's no more data
                         * in the region, so clear the rest of the buffer and
                         * return success.
                         */
                        ret = -ENODATA;
                        if (read_hole == NETFS_READ_HOLE_FAIL)
                                goto presubmission_error;

                        iov_iter_zero(len, iter);
                        skipped = len;
                        ret = 0;
                        goto presubmission_error;
                }

                skipped = off2 - off;
                iov_iter_zero(skipped, iter);
        }

        ret = -ENOMEM;
        ki = kzalloc_obj(struct cachefiles_kiocb);
        if (!ki)
                goto presubmission_error;

        refcount_set(&ki->ki_refcnt, 2);
        ki->iocb.ki_filp        = file;
        ki->iocb.ki_pos         = start_pos + skipped;
        ki->iocb.ki_flags       = IOCB_DIRECT;
        ki->iocb.ki_ioprio      = get_current_ioprio();
        ki->skipped             = skipped;
        ki->object              = object;
        ki->inval_counter       = cres->inval_counter;
        ki->term_func           = term_func;
        ki->term_func_priv      = term_func_priv;
        ki->was_async           = true;

        if (ki->term_func)
                ki->iocb.ki_complete = cachefiles_read_complete;

        get_file(ki->iocb.ki_filp);
        cachefiles_grab_object(object, cachefiles_obj_get_ioreq);

        trace_cachefiles_read(object, file_inode(file), ki->iocb.ki_pos, len - skipped);
        old_nofs = memalloc_nofs_save();
        ret = cachefiles_inject_read_error();
        if (ret == 0)
                ret = vfs_iocb_iter_read(file, &ki->iocb, iter);
        memalloc_nofs_restore(old_nofs);
        switch (ret) {
        case -EIOCBQUEUED:
                goto in_progress;

        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /* There's no easy way to restart the syscall since other AIO's
                 * may be already running. Just fail this IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                ki->was_async = false;
                cachefiles_read_complete(&ki->iocb, ret);
                if (ret > 0)
                        ret = 0;
                break;
        }

in_progress:
        cachefiles_put_kiocb(ki);
        _leave(" = %zd", ret);
        return ret;

presubmission_error:
        if (term_func)
                term_func(term_func_priv, ret < 0 ? ret : skipped);
        return ret;
}

/*
 * Query the occupancy of the cache in a region, returning where the next chunk
 * of data starts and how long it is.
 */
static int cachefiles_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 cachefiles_object *object;
        struct file *file;
        loff_t off, off2;

        *_data_start = -1;
        *_data_len = 0;

        if (!fscache_wait_for_operation(cres, FSCACHE_WANT_READ))
                return -ENOBUFS;

        object = cachefiles_cres_object(cres);
        file = cachefiles_cres_file(cres);
        granularity = max_t(size_t, object->volume->cache->bsize, granularity);

        _enter("%pD,%li,%llx,%zx/%llx",
               file, file_inode(file)->i_ino, start, len,
               i_size_read(file_inode(file)));

        off = cachefiles_inject_read_error();
        if (off == 0)
                off = vfs_llseek(file, start, SEEK_DATA);
        if (off == -ENXIO)
                return -ENODATA; /* Beyond EOF */
        if (off < 0 && off >= (loff_t)-MAX_ERRNO)
                return -ENOBUFS; /* Error. */
        if (round_up(off, granularity) >= start + len)
                return -ENODATA; /* No data in range */

        off2 = cachefiles_inject_read_error();
        if (off2 == 0)
                off2 = vfs_llseek(file, off, SEEK_HOLE);
        if (off2 == -ENXIO)
                return -ENODATA; /* Beyond EOF */
        if (off2 < 0 && off2 >= (loff_t)-MAX_ERRNO)
                return -ENOBUFS; /* Error. */

        /* Round away partial blocks */
        off = round_up(off, granularity);
        off2 = round_down(off2, granularity);
        if (off2 <= off)
                return -ENODATA;

        *_data_start = off;
        if (off2 > start + len)
                *_data_len = len;
        else
                *_data_len = off2 - off;
        return 0;
}

/*
 * Handle completion of a write to the cache.
 */
static void cachefiles_write_complete(struct kiocb *iocb, long ret)
{
        struct cachefiles_kiocb *ki = container_of(iocb, struct cachefiles_kiocb, iocb);
        struct cachefiles_object *object = ki->object;
        struct inode *inode = file_inode(ki->iocb.ki_filp);

        _enter("%ld", ret);

        if (ki->was_async)
                kiocb_end_write(iocb);

        if (ret < 0)
                trace_cachefiles_io_error(object, inode, ret,
                                          cachefiles_trace_write_error);

        atomic_long_sub(ki->b_writing, &object->volume->cache->b_writing);
        set_bit(FSCACHE_COOKIE_HAVE_DATA, &object->cookie->flags);
        if (ki->term_func)
                ki->term_func(ki->term_func_priv, ret);
        cachefiles_put_kiocb(ki);
}

/*
 * Initiate a write to the cache.
 */
int __cachefiles_write(struct cachefiles_object *object,
                       struct file *file,
                       loff_t start_pos,
                       struct iov_iter *iter,
                       netfs_io_terminated_t term_func,
                       void *term_func_priv)
{
        struct cachefiles_cache *cache;
        struct cachefiles_kiocb *ki;
        unsigned int old_nofs;
        ssize_t ret;
        size_t len = iov_iter_count(iter);

        fscache_count_write();
        cache = object->volume->cache;

        _enter("%pD,%li,%llx,%zx/%llx",
               file, file_inode(file)->i_ino, start_pos, len,
               i_size_read(file_inode(file)));

        ki = kzalloc_obj(struct cachefiles_kiocb);
        if (!ki) {
                if (term_func)
                        term_func(term_func_priv, -ENOMEM);
                return -ENOMEM;
        }

        refcount_set(&ki->ki_refcnt, 2);
        ki->iocb.ki_filp        = file;
        ki->iocb.ki_pos         = start_pos;
        ki->iocb.ki_flags       = IOCB_DIRECT | IOCB_WRITE;
        ki->iocb.ki_ioprio      = get_current_ioprio();
        ki->object              = object;
        ki->start               = start_pos;
        ki->len                 = len;
        ki->term_func           = term_func;
        ki->term_func_priv      = term_func_priv;
        ki->was_async           = true;
        ki->b_writing           = (len + (1 << cache->bshift) - 1) >> cache->bshift;

        if (ki->term_func)
                ki->iocb.ki_complete = cachefiles_write_complete;
        atomic_long_add(ki->b_writing, &cache->b_writing);

        get_file(ki->iocb.ki_filp);
        cachefiles_grab_object(object, cachefiles_obj_get_ioreq);

        trace_cachefiles_write(object, file_inode(file), ki->iocb.ki_pos, len);
        old_nofs = memalloc_nofs_save();
        ret = cachefiles_inject_write_error();
        if (ret == 0)
                ret = vfs_iocb_iter_write(file, &ki->iocb, iter);
        memalloc_nofs_restore(old_nofs);
        switch (ret) {
        case -EIOCBQUEUED:
                goto in_progress;

        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /* There's no easy way to restart the syscall since other AIO's
                 * may be already running. Just fail this IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                ki->was_async = false;
                cachefiles_write_complete(&ki->iocb, ret);
                break;
        }

in_progress:
        cachefiles_put_kiocb(ki);
        _leave(" = %zd", ret);
        return ret;
}

static int cachefiles_write(struct netfs_cache_resources *cres,
                            loff_t start_pos,
                            struct iov_iter *iter,
                            netfs_io_terminated_t term_func,
                            void *term_func_priv)
{
        if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE)) {
                if (term_func)
                        term_func(term_func_priv, -ENOBUFS);
                trace_netfs_sreq(term_func_priv, netfs_sreq_trace_cache_nowrite);
                return -ENOBUFS;
        }

        return __cachefiles_write(cachefiles_cres_object(cres),
                                  cachefiles_cres_file(cres),
                                  start_pos, iter,
                                  term_func, term_func_priv);
}

static inline enum netfs_io_source
cachefiles_do_prepare_read(struct netfs_cache_resources *cres,
                           loff_t start, size_t *_len, loff_t i_size,
                           unsigned long *_flags, ino_t netfs_ino)
{
        enum cachefiles_prepare_read_trace why;
        struct cachefiles_object *object = NULL;
        struct cachefiles_cache *cache;
        struct fscache_cookie *cookie = fscache_cres_cookie(cres);
        const struct cred *saved_cred;
        struct file *file = cachefiles_cres_file(cres);
        enum netfs_io_source ret = NETFS_DOWNLOAD_FROM_SERVER;
        size_t len = *_len;
        loff_t off, to;
        ino_t ino = file ? file_inode(file)->i_ino : 0;
        int rc;

        _enter("%zx @%llx/%llx", len, start, i_size);

        if (start >= i_size) {
                ret = NETFS_FILL_WITH_ZEROES;
                why = cachefiles_trace_read_after_eof;
                goto out_no_object;
        }

        if (test_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags)) {
                __set_bit(NETFS_SREQ_COPY_TO_CACHE, _flags);
                why = cachefiles_trace_read_no_data;
                if (!test_bit(NETFS_SREQ_ONDEMAND, _flags))
                        goto out_no_object;
        }

        /* The object and the file may be being created in the background. */
        if (!file) {
                why = cachefiles_trace_read_no_file;
                if (!fscache_wait_for_operation(cres, FSCACHE_WANT_READ))
                        goto out_no_object;
                file = cachefiles_cres_file(cres);
                if (!file)
                        goto out_no_object;
                ino = file_inode(file)->i_ino;
        }

        object = cachefiles_cres_object(cres);
        cache = object->volume->cache;
        cachefiles_begin_secure(cache, &saved_cred);
retry:
        off = cachefiles_inject_read_error();
        if (off == 0)
                off = vfs_llseek(file, start, SEEK_DATA);
        if (off < 0 && off >= (loff_t)-MAX_ERRNO) {
                if (off == (loff_t)-ENXIO) {
                        why = cachefiles_trace_read_seek_nxio;
                        goto download_and_store;
                }
                trace_cachefiles_io_error(object, file_inode(file), off,
                                          cachefiles_trace_seek_error);
                why = cachefiles_trace_read_seek_error;
                goto out;
        }

        if (off >= start + len) {
                why = cachefiles_trace_read_found_hole;
                goto download_and_store;
        }

        if (off > start) {
                off = round_up(off, cache->bsize);
                len = off - start;
                *_len = len;
                why = cachefiles_trace_read_found_part;
                goto download_and_store;
        }

        to = cachefiles_inject_read_error();
        if (to == 0)
                to = vfs_llseek(file, start, SEEK_HOLE);
        if (to < 0 && to >= (loff_t)-MAX_ERRNO) {
                trace_cachefiles_io_error(object, file_inode(file), to,
                                          cachefiles_trace_seek_error);
                why = cachefiles_trace_read_seek_error;
                goto out;
        }

        if (to < start + len) {
                if (start + len >= i_size)
                        to = round_up(to, cache->bsize);
                else
                        to = round_down(to, cache->bsize);
                len = to - start;
                *_len = len;
        }

        why = cachefiles_trace_read_have_data;
        ret = NETFS_READ_FROM_CACHE;
        goto out;

download_and_store:
        __set_bit(NETFS_SREQ_COPY_TO_CACHE, _flags);
        if (test_bit(NETFS_SREQ_ONDEMAND, _flags)) {
                rc = cachefiles_ondemand_read(object, start, len);
                if (!rc) {
                        __clear_bit(NETFS_SREQ_ONDEMAND, _flags);
                        goto retry;
                }
                ret = NETFS_INVALID_READ;
        }
out:
        cachefiles_end_secure(cache, saved_cred);
out_no_object:
        trace_cachefiles_prep_read(object, start, len, *_flags, ret, why, ino, netfs_ino);
        return ret;
}

/*
 * Prepare a read operation, shortening it to a cached/uncached
 * boundary as appropriate.
 */
static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *subreq,
                                                    unsigned long long i_size)
{
        return cachefiles_do_prepare_read(&subreq->rreq->cache_resources,
                                          subreq->start, &subreq->len, i_size,
                                          &subreq->flags, subreq->rreq->inode->i_ino);
}

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

/*
 * Prepare for a write to occur.
 */
int __cachefiles_prepare_write(struct cachefiles_object *object,
                               struct file *file,
                               loff_t *_start, size_t *_len, size_t upper_len,
                               bool no_space_allocated_yet)
{
        struct cachefiles_cache *cache = object->volume->cache;
        loff_t start = *_start, pos;
        size_t len = *_len;
        int ret;

        /* Round to DIO size */
        start = round_down(*_start, PAGE_SIZE);
        if (start != *_start || *_len > upper_len) {
                /* Probably asked to cache a streaming write written into the
                 * pagecache when the cookie was temporarily out of service to
                 * culling.
                 */
                fscache_count_dio_misfit();
                return -ENOBUFS;
        }

        *_len = round_up(len, PAGE_SIZE);

        /* We need to work out whether there's sufficient disk space to perform
         * the write - but we can skip that check if we have space already
         * allocated.
         */
        if (no_space_allocated_yet)
                goto check_space;

        pos = cachefiles_inject_read_error();
        if (pos == 0)
                pos = vfs_llseek(file, start, SEEK_DATA);
        if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
                if (pos == -ENXIO)
                        goto check_space; /* Unallocated tail */
                trace_cachefiles_io_error(object, file_inode(file), pos,
                                          cachefiles_trace_seek_error);
                return pos;
        }
        if ((u64)pos >= (u64)start + *_len)
                goto check_space; /* Unallocated region */

        /* We have a block that's at least partially filled - if we're low on
         * space, we need to see if it's fully allocated.  If it's not, we may
         * want to cull it.
         */
        if (cachefiles_has_space(cache, 0, *_len / PAGE_SIZE,
                                 cachefiles_has_space_check) == 0)
                return 0; /* Enough space to simply overwrite the whole block */

        pos = cachefiles_inject_read_error();
        if (pos == 0)
                pos = vfs_llseek(file, start, SEEK_HOLE);
        if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
                trace_cachefiles_io_error(object, file_inode(file), pos,
                                          cachefiles_trace_seek_error);
                return pos;
        }
        if ((u64)pos >= (u64)start + *_len)
                return 0; /* Fully allocated */

        /* Partially allocated, but insufficient space: cull. */
        fscache_count_no_write_space();
        ret = cachefiles_inject_remove_error();
        if (ret == 0)
                ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                                    start, *_len);
        if (ret < 0) {
                trace_cachefiles_io_error(object, file_inode(file), ret,
                                          cachefiles_trace_fallocate_error);
                cachefiles_io_error_obj(object,
                                        "CacheFiles: fallocate failed (%d)\n", ret);
                ret = -EIO;
        }

        return ret;

check_space:
        return cachefiles_has_space(cache, 0, *_len / PAGE_SIZE,
                                    cachefiles_has_space_for_write);
}

static int cachefiles_prepare_write(struct netfs_cache_resources *cres,
                                    loff_t *_start, size_t *_len, size_t upper_len,
                                    loff_t i_size, bool no_space_allocated_yet)
{
        struct cachefiles_object *object = cachefiles_cres_object(cres);
        struct cachefiles_cache *cache = object->volume->cache;
        const struct cred *saved_cred;
        int ret;

        if (!cachefiles_cres_file(cres)) {
                if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE))
                        return -ENOBUFS;
                if (!cachefiles_cres_file(cres))
                        return -ENOBUFS;
        }

        cachefiles_begin_secure(cache, &saved_cred);
        ret = __cachefiles_prepare_write(object, cachefiles_cres_file(cres),
                                         _start, _len, upper_len,
                                         no_space_allocated_yet);
        cachefiles_end_secure(cache, saved_cred);
        return ret;
}

static void cachefiles_prepare_write_subreq(struct netfs_io_subrequest *subreq)
{
        struct netfs_io_request *wreq = subreq->rreq;
        struct netfs_cache_resources *cres = &wreq->cache_resources;
        struct netfs_io_stream *stream = &wreq->io_streams[subreq->stream_nr];

        _enter("W=%x[%x] %llx", wreq->debug_id, subreq->debug_index, subreq->start);

        stream->sreq_max_len = MAX_RW_COUNT;
        stream->sreq_max_segs = BIO_MAX_VECS;

        if (!cachefiles_cres_file(cres)) {
                if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE))
                        return netfs_prepare_write_failed(subreq);
                if (!cachefiles_cres_file(cres))
                        return netfs_prepare_write_failed(subreq);
        }
}

static void cachefiles_issue_write(struct netfs_io_subrequest *subreq)
{
        struct netfs_io_request *wreq = subreq->rreq;
        struct netfs_cache_resources *cres = &wreq->cache_resources;
        struct cachefiles_object *object = cachefiles_cres_object(cres);
        struct cachefiles_cache *cache = object->volume->cache;
        struct netfs_io_stream *stream = &wreq->io_streams[subreq->stream_nr];
        const struct cred *saved_cred;
        size_t off, pre, post, len = subreq->len;
        loff_t start = subreq->start;
        int ret;

        _enter("W=%x[%x] %llx-%llx",
               wreq->debug_id, subreq->debug_index, start, start + len - 1);

        /* We need to start on the cache granularity boundary */
        off = start & (CACHEFILES_DIO_BLOCK_SIZE - 1);
        if (off) {
                pre = CACHEFILES_DIO_BLOCK_SIZE - off;
                if (pre >= len) {
                        fscache_count_dio_misfit();
                        netfs_write_subrequest_terminated(subreq, len);
                        return;
                }
                subreq->transferred += pre;
                start += pre;
                len -= pre;
                iov_iter_advance(&subreq->io_iter, pre);
        }

        /* We also need to end on the cache granularity boundary */
        if (start + len == wreq->i_size) {
                size_t part = len % CACHEFILES_DIO_BLOCK_SIZE;
                size_t need = CACHEFILES_DIO_BLOCK_SIZE - part;

                if (part && stream->submit_extendable_to >= need) {
                        len += need;
                        subreq->len += need;
                        subreq->io_iter.count += need;
                }
        }

        post = len & (CACHEFILES_DIO_BLOCK_SIZE - 1);
        if (post) {
                len -= post;
                if (len == 0) {
                        fscache_count_dio_misfit();
                        netfs_write_subrequest_terminated(subreq, post);
                        return;
                }
                iov_iter_truncate(&subreq->io_iter, len);
        }

        trace_netfs_sreq(subreq, netfs_sreq_trace_cache_prepare);
        cachefiles_begin_secure(cache, &saved_cred);
        ret = __cachefiles_prepare_write(object, cachefiles_cres_file(cres),
                                         &start, &len, len, true);
        cachefiles_end_secure(cache, saved_cred);
        if (ret < 0) {
                netfs_write_subrequest_terminated(subreq, ret);
                return;
        }

        trace_netfs_sreq(subreq, netfs_sreq_trace_cache_write);
        cachefiles_write(&subreq->rreq->cache_resources,
                         subreq->start, &subreq->io_iter,
                         netfs_write_subrequest_terminated, subreq);
}

/*
 * Clean up an operation.
 */
static void cachefiles_end_operation(struct netfs_cache_resources *cres)
{
        struct file *file = cachefiles_cres_file(cres);

        if (file)
                fput(file);
        fscache_end_cookie_access(fscache_cres_cookie(cres), fscache_access_io_end);
}

static const struct netfs_cache_ops cachefiles_netfs_cache_ops = {
        .end_operation          = cachefiles_end_operation,
        .read                   = cachefiles_read,
        .write                  = cachefiles_write,
        .issue_write            = cachefiles_issue_write,
        .prepare_read           = cachefiles_prepare_read,
        .prepare_write          = cachefiles_prepare_write,
        .prepare_write_subreq   = cachefiles_prepare_write_subreq,
        .prepare_ondemand_read  = cachefiles_prepare_ondemand_read,
        .query_occupancy        = cachefiles_query_occupancy,
};

/*
 * Open the cache file when beginning a cache operation.
 */
bool cachefiles_begin_operation(struct netfs_cache_resources *cres,
                                enum fscache_want_state want_state)
{
        struct cachefiles_object *object = cachefiles_cres_object(cres);

        if (!cachefiles_cres_file(cres)) {
                cres->ops = &cachefiles_netfs_cache_ops;
                if (object->file) {
                        spin_lock(&object->lock);
                        if (!cres->cache_priv2 && object->file)
                                cres->cache_priv2 = get_file(object->file);
                        spin_unlock(&object->lock);
                }
        }

        if (!cachefiles_cres_file(cres) && want_state != FSCACHE_WANT_PARAMS) {
                pr_err("failed to get cres->file\n");
                return false;
        }

        return true;
}