// SPDX-License-Identifier: GPL-2.0-or-later
/* Direct I/O support.
 *
 * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/export.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include <linux/sched/mm.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/netfs.h>
#include "internal.h"

static void netfs_prepare_dio_read_iterator(struct netfs_io_subrequest *subreq)
{
        struct netfs_io_request *rreq = subreq->rreq;
        size_t rsize;

        rsize = umin(subreq->len, rreq->io_streams[0].sreq_max_len);
        subreq->len = rsize;

        if (unlikely(rreq->io_streams[0].sreq_max_segs)) {
                size_t limit = netfs_limit_iter(&rreq->buffer.iter, 0, rsize,
                                                rreq->io_streams[0].sreq_max_segs);

                if (limit < rsize) {
                        subreq->len = limit;
                        trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
                }
        }

        trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);

        subreq->io_iter = rreq->buffer.iter;
        iov_iter_truncate(&subreq->io_iter, subreq->len);
        iov_iter_advance(&rreq->buffer.iter, subreq->len);
}

/*
 * Perform a read to a buffer from the server, slicing up the region to be read
 * according to the network rsize.
 */
static int netfs_dispatch_unbuffered_reads(struct netfs_io_request *rreq)
{
        struct netfs_io_stream *stream = &rreq->io_streams[0];
        unsigned long long start = rreq->start;
        ssize_t size = rreq->len;
        int ret = 0;

        do {
                struct netfs_io_subrequest *subreq;
                ssize_t slice;

                subreq = netfs_alloc_subrequest(rreq);
                if (!subreq) {
                        ret = -ENOMEM;
                        break;
                }

                subreq->source  = NETFS_DOWNLOAD_FROM_SERVER;
                subreq->start   = start;
                subreq->len     = size;

                __set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);

                spin_lock(&rreq->lock);
                list_add_tail(&subreq->rreq_link, &stream->subrequests);
                if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
                        if (!stream->active) {
                                stream->collected_to = subreq->start;
                                /* Store list pointers before active flag */
                                smp_store_release(&stream->active, true);
                        }
                }
                trace_netfs_sreq(subreq, netfs_sreq_trace_added);
                spin_unlock(&rreq->lock);

                netfs_stat(&netfs_n_rh_download);
                if (rreq->netfs_ops->prepare_read) {
                        ret = rreq->netfs_ops->prepare_read(subreq);
                        if (ret < 0) {
                                netfs_put_subrequest(subreq, netfs_sreq_trace_put_cancel);
                                break;
                        }
                }

                netfs_prepare_dio_read_iterator(subreq);
                slice = subreq->len;
                size -= slice;
                start += slice;
                rreq->submitted += slice;
                if (size <= 0) {
                        smp_wmb(); /* Write lists before ALL_QUEUED. */
                        set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
                }

                rreq->netfs_ops->issue_read(subreq);

                if (test_bit(NETFS_RREQ_PAUSE, &rreq->flags))
                        netfs_wait_for_paused_read(rreq);
                if (test_bit(NETFS_RREQ_FAILED, &rreq->flags))
                        break;
                cond_resched();
        } while (size > 0);

        if (unlikely(size > 0)) {
                smp_wmb(); /* Write lists before ALL_QUEUED. */
                set_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags);
                netfs_wake_collector(rreq);
        }

        return ret;
}

/*
 * Perform a read to an application buffer, bypassing the pagecache and the
 * local disk cache.
 */
static ssize_t netfs_unbuffered_read(struct netfs_io_request *rreq, bool sync)
{
        ssize_t ret;

        _enter("R=%x %llx-%llx",
               rreq->debug_id, rreq->start, rreq->start + rreq->len - 1);

        if (rreq->len == 0) {
                pr_err("Zero-sized read [R=%x]\n", rreq->debug_id);
                netfs_put_request(rreq, netfs_rreq_trace_put_discard);
                return -EIO;
        }

        // TODO: Use bounce buffer if requested

        inode_dio_begin(rreq->inode);

        ret = netfs_dispatch_unbuffered_reads(rreq);

        if (!rreq->submitted) {
                netfs_put_request(rreq, netfs_rreq_trace_put_no_submit);
                inode_dio_end(rreq->inode);
                ret = 0;
                goto out;
        }

        if (sync)
                ret = netfs_wait_for_read(rreq);
        else
                ret = -EIOCBQUEUED;
out:
        _leave(" = %zd", ret);
        return ret;
}

/**
 * netfs_unbuffered_read_iter_locked - Perform an unbuffered or direct I/O read
 * @iocb: The I/O control descriptor describing the read
 * @iter: The output buffer (also specifies read length)
 *
 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
 * output buffer.  No use is made of the pagecache.
 *
 * The caller must hold any appropriate locks.
 */
ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *iter)
{
        struct netfs_io_request *rreq;
        ssize_t ret;
        size_t orig_count = iov_iter_count(iter);
        bool sync = is_sync_kiocb(iocb);

        _enter("");

        if (!orig_count)
                return 0; /* Don't update atime */

        ret = kiocb_write_and_wait(iocb, orig_count);
        if (ret < 0)
                return ret;
        file_accessed(iocb->ki_filp);

        rreq = netfs_alloc_request(iocb->ki_filp->f_mapping, iocb->ki_filp,
                                   iocb->ki_pos, orig_count,
                                   iocb->ki_flags & IOCB_DIRECT ?
                                   NETFS_DIO_READ : NETFS_UNBUFFERED_READ);
        if (IS_ERR(rreq))
                return PTR_ERR(rreq);

        netfs_stat(&netfs_n_rh_dio_read);
        trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_dio_read);

        /* If this is an async op, we have to keep track of the destination
         * buffer for ourselves as the caller's iterator will be trashed when
         * we return.
         *
         * In such a case, extract an iterator to represent as much of the the
         * output buffer as we can manage.  Note that the extraction might not
         * be able to allocate a sufficiently large bvec array and may shorten
         * the request.
         */
        if (user_backed_iter(iter)) {
                ret = netfs_extract_user_iter(iter, rreq->len, &rreq->buffer.iter, 0);
                if (ret < 0)
                        goto error_put;
                rreq->direct_bv = (struct bio_vec *)rreq->buffer.iter.bvec;
                rreq->direct_bv_count = ret;
                rreq->direct_bv_unpin = iov_iter_extract_will_pin(iter);
                rreq->len = iov_iter_count(&rreq->buffer.iter);
        } else {
                rreq->buffer.iter = *iter;
                rreq->len = orig_count;
                rreq->direct_bv_unpin = false;
                iov_iter_advance(iter, orig_count);
        }

        // TODO: Set up bounce buffer if needed

        if (!sync) {
                rreq->iocb = iocb;
                __set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags);
        }

        ret = netfs_unbuffered_read(rreq, sync);
        if (ret < 0)
                goto out; /* May be -EIOCBQUEUED */
        if (sync) {
                // TODO: Copy from bounce buffer
                iocb->ki_pos += rreq->transferred;
                ret = rreq->transferred;
        }

out:
        netfs_put_request(rreq, netfs_rreq_trace_put_return);
        if (ret > 0)
                orig_count -= ret;
        return ret;

error_put:
        netfs_put_failed_request(rreq);
        return ret;
}
EXPORT_SYMBOL(netfs_unbuffered_read_iter_locked);

/**
 * netfs_unbuffered_read_iter - Perform an unbuffered or direct I/O read
 * @iocb: The I/O control descriptor describing the read
 * @iter: The output buffer (also specifies read length)
 *
 * Perform an unbuffered I/O or direct I/O from the file in @iocb to the
 * output buffer.  No use is made of the pagecache.
 */
ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
        struct inode *inode = file_inode(iocb->ki_filp);
        ssize_t ret;

        if (!iter->count)
                return 0; /* Don't update atime */

        ret = netfs_start_io_direct(inode);
        if (ret == 0) {
                ret = netfs_unbuffered_read_iter_locked(iocb, iter);
                netfs_end_io_direct(inode);
        }
        return ret;
}
EXPORT_SYMBOL(netfs_unbuffered_read_iter);