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

#include <linux/export.h>
#include <linux/uio.h>
#include "internal.h"

/*
 * Perform the cleanup rituals after an unbuffered write is complete.
 */
static void netfs_unbuffered_write_done(struct netfs_io_request *wreq)
{
        struct netfs_inode *ictx = netfs_inode(wreq->inode);

        _enter("R=%x", wreq->debug_id);

        /* Okay, declare that all I/O is complete. */
        trace_netfs_rreq(wreq, netfs_rreq_trace_write_done);

        if (!wreq->error)
                netfs_update_i_size(ictx, &ictx->inode, wreq->start, wreq->transferred);

        if (wreq->origin == NETFS_DIO_WRITE &&
            wreq->mapping->nrpages) {
                /* mmap may have got underfoot and we may now have folios
                 * locally covering the region we just wrote.  Attempt to
                 * discard the folios, but leave in place any modified locally.
                 * ->write_iter() is prevented from interfering by the DIO
                 * counter.
                 */
                pgoff_t first = wreq->start >> PAGE_SHIFT;
                pgoff_t last = (wreq->start + wreq->transferred - 1) >> PAGE_SHIFT;

                invalidate_inode_pages2_range(wreq->mapping, first, last);
        }

        if (wreq->origin == NETFS_DIO_WRITE)
                inode_dio_end(wreq->inode);

        _debug("finished");
        netfs_wake_rreq_flag(wreq, NETFS_RREQ_IN_PROGRESS, netfs_rreq_trace_wake_ip);
        /* As we cleared NETFS_RREQ_IN_PROGRESS, we acquired its ref. */

        if (wreq->iocb) {
                size_t written = umin(wreq->transferred, wreq->len);

                wreq->iocb->ki_pos += written;
                if (wreq->iocb->ki_complete) {
                        trace_netfs_rreq(wreq, netfs_rreq_trace_ki_complete);
                        wreq->iocb->ki_complete(wreq->iocb, wreq->error ?: written);
                }
                wreq->iocb = VFS_PTR_POISON;
        }

        netfs_clear_subrequests(wreq);
}

/*
 * Collect the subrequest results of unbuffered write subrequests.
 */
static void netfs_unbuffered_write_collect(struct netfs_io_request *wreq,
                                           struct netfs_io_stream *stream,
                                           struct netfs_io_subrequest *subreq)
{
        trace_netfs_collect_sreq(wreq, subreq);

        spin_lock(&wreq->lock);
        list_del_init(&subreq->rreq_link);
        spin_unlock(&wreq->lock);

        wreq->transferred += subreq->transferred;
        iov_iter_advance(&wreq->buffer.iter, subreq->transferred);

        stream->collected_to = subreq->start + subreq->transferred;
        wreq->collected_to = stream->collected_to;
        netfs_put_subrequest(subreq, netfs_sreq_trace_put_done);

        trace_netfs_collect_stream(wreq, stream);
        trace_netfs_collect_state(wreq, wreq->collected_to, 0);
}

/*
 * Write data to the server without going through the pagecache and without
 * writing it to the local cache.  We dispatch the subrequests serially and
 * wait for each to complete before dispatching the next, lest we leave a gap
 * in the data written due to a failure such as ENOSPC.  We could, however
 * attempt to do preparation such as content encryption for the next subreq
 * whilst the current is in progress.
 */
static int netfs_unbuffered_write(struct netfs_io_request *wreq)
{
        struct netfs_io_subrequest *subreq = NULL;
        struct netfs_io_stream *stream = &wreq->io_streams[0];
        int ret;

        _enter("%llx", wreq->len);

        if (wreq->origin == NETFS_DIO_WRITE)
                inode_dio_begin(wreq->inode);

        stream->collected_to = wreq->start;

        for (;;) {
                bool retry = false;

                if (!subreq) {
                        netfs_prepare_write(wreq, stream, wreq->start + wreq->transferred);
                        subreq = stream->construct;
                        stream->construct = NULL;
                }

                /* Check if (re-)preparation failed. */
                if (unlikely(test_bit(NETFS_SREQ_FAILED, &subreq->flags))) {
                        netfs_write_subrequest_terminated(subreq, subreq->error);
                        wreq->error = subreq->error;
                        break;
                }

                iov_iter_truncate(&subreq->io_iter, wreq->len - wreq->transferred);
                if (!iov_iter_count(&subreq->io_iter))
                        break;

                subreq->len = netfs_limit_iter(&subreq->io_iter, 0,
                                               stream->sreq_max_len,
                                               stream->sreq_max_segs);
                iov_iter_truncate(&subreq->io_iter, subreq->len);
                stream->submit_extendable_to = subreq->len;

                trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
                stream->issue_write(subreq);

                /* Async, need to wait. */
                netfs_wait_for_in_progress_stream(wreq, stream);

                if (test_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags)) {
                        retry = true;
                } else if (test_bit(NETFS_SREQ_FAILED, &subreq->flags)) {
                        ret = subreq->error;
                        wreq->error = ret;
                        netfs_see_subrequest(subreq, netfs_sreq_trace_see_failed);
                        subreq = NULL;
                        break;
                }
                ret = 0;

                if (!retry) {
                        netfs_unbuffered_write_collect(wreq, stream, subreq);
                        subreq = NULL;
                        if (wreq->transferred >= wreq->len)
                                break;
                        if (!wreq->iocb && signal_pending(current)) {
                                ret = wreq->transferred ? -EINTR : -ERESTARTSYS;
                                trace_netfs_rreq(wreq, netfs_rreq_trace_intr);
                                break;
                        }
                        continue;
                }

                /* We need to retry the last subrequest, so first reset the
                 * iterator, taking into account what, if anything, we managed
                 * to transfer.
                 */
                subreq->error = -EAGAIN;
                trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
                if (subreq->transferred > 0)
                        iov_iter_advance(&wreq->buffer.iter, subreq->transferred);

                if (stream->source == NETFS_UPLOAD_TO_SERVER &&
                    wreq->netfs_ops->retry_request)
                        wreq->netfs_ops->retry_request(wreq, stream);

                __clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
                __clear_bit(NETFS_SREQ_BOUNDARY, &subreq->flags);
                __clear_bit(NETFS_SREQ_FAILED, &subreq->flags);
                subreq->io_iter         = wreq->buffer.iter;
                subreq->start           = wreq->start + wreq->transferred;
                subreq->len             = wreq->len   - wreq->transferred;
                subreq->transferred     = 0;
                subreq->retry_count     += 1;
                stream->sreq_max_len    = UINT_MAX;
                stream->sreq_max_segs   = INT_MAX;

                netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);

                if (stream->prepare_write) {
                        stream->prepare_write(subreq);
                        __set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
                        netfs_stat(&netfs_n_wh_retry_write_subreq);
                } else {
                        struct iov_iter source;

                        netfs_reset_iter(subreq);
                        source = subreq->io_iter;
                        netfs_reissue_write(stream, subreq, &source);
                }
        }

        netfs_unbuffered_write_done(wreq);
        _leave(" = %d", ret);
        return ret;
}

static void netfs_unbuffered_write_async(struct work_struct *work)
{
        struct netfs_io_request *wreq = container_of(work, struct netfs_io_request, work);

        netfs_unbuffered_write(wreq);
        netfs_put_request(wreq, netfs_rreq_trace_put_complete);
}

/*
 * Perform an unbuffered write where we may have to do an RMW operation on an
 * encrypted file.  This can also be used for direct I/O writes.
 */
ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
                                                  struct netfs_group *netfs_group)
{
        struct netfs_io_request *wreq;
        unsigned long long start = iocb->ki_pos;
        unsigned long long end = start + iov_iter_count(iter);
        ssize_t ret, n;
        size_t len = iov_iter_count(iter);
        bool async = !is_sync_kiocb(iocb);

        _enter("");

        /* We're going to need a bounce buffer if what we transmit is going to
         * be different in some way to the source buffer, e.g. because it gets
         * encrypted/compressed or because it needs expanding to a block size.
         */
        // TODO

        _debug("uw %llx-%llx", start, end);

        wreq = netfs_create_write_req(iocb->ki_filp->f_mapping, iocb->ki_filp, start,
                                      iocb->ki_flags & IOCB_DIRECT ?
                                      NETFS_DIO_WRITE : NETFS_UNBUFFERED_WRITE);
        if (IS_ERR(wreq))
                return PTR_ERR(wreq);

        wreq->io_streams[0].avail = true;
        trace_netfs_write(wreq, (iocb->ki_flags & IOCB_DIRECT ?
                                 netfs_write_trace_dio_write :
                                 netfs_write_trace_unbuffered_write));

        {
                /* If this is an async op and we're not using a bounce buffer,
                 * we have to save the source buffer as the iterator is only
                 * good until 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)) {
                        n = netfs_extract_user_iter(iter, len, &wreq->buffer.iter, 0);
                        if (n < 0) {
                                ret = n;
                                goto error_put;
                        }
                        wreq->direct_bv = (struct bio_vec *)wreq->buffer.iter.bvec;
                        wreq->direct_bv_count = n;
                        wreq->direct_bv_unpin = iov_iter_extract_will_pin(iter);
                } else {
                        /* If this is a kernel-generated async DIO request,
                         * assume that any resources the iterator points to
                         * (eg. a bio_vec array) will persist till the end of
                         * the op.
                         */
                        wreq->buffer.iter = *iter;
                }

                wreq->len = iov_iter_count(&wreq->buffer.iter);
        }

        __set_bit(NETFS_RREQ_USE_IO_ITER, &wreq->flags);

        /* Copy the data into the bounce buffer and encrypt it. */
        // TODO

        /* Dispatch the write. */
        __set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);

        if (async) {
                INIT_WORK(&wreq->work, netfs_unbuffered_write_async);
                wreq->iocb = iocb;
                queue_work(system_dfl_wq, &wreq->work);
                ret = -EIOCBQUEUED;
        } else {
                ret = netfs_unbuffered_write(wreq);
                if (ret < 0) {
                        _debug("begin = %zd", ret);
                } else {
                        iocb->ki_pos += wreq->transferred;
                        ret = wreq->transferred ?: wreq->error;
                }

                netfs_put_request(wreq, netfs_rreq_trace_put_complete);
        }

        netfs_put_request(wreq, netfs_rreq_trace_put_return);
        return ret;

error_put:
        netfs_put_failed_request(wreq);
        return ret;
}
EXPORT_SYMBOL(netfs_unbuffered_write_iter_locked);

/**
 * netfs_unbuffered_write_iter - Unbuffered write to a file
 * @iocb: IO state structure
 * @from: iov_iter with data to write
 *
 * Do an unbuffered write to a file, writing the data directly to the server
 * and not lodging the data in the pagecache.
 *
 * Return:
 * * Negative error code if no data has been written at all of
 *   vfs_fsync_range() failed for a synchronous write
 * * Number of bytes written, even for truncated writes
 */
ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct netfs_inode *ictx = netfs_inode(inode);
        ssize_t ret;
        loff_t pos = iocb->ki_pos;
        unsigned long long end = pos + iov_iter_count(from) - 1;

        _enter("%llx,%zx,%llx", pos, iov_iter_count(from), i_size_read(inode));

        if (!iov_iter_count(from))
                return 0;

        trace_netfs_write_iter(iocb, from);
        netfs_stat(&netfs_n_wh_dio_write);

        ret = netfs_start_io_direct(inode);
        if (ret < 0)
                return ret;
        ret = generic_write_checks(iocb, from);
        if (ret <= 0)
                goto out;
        ret = file_remove_privs(file);
        if (ret < 0)
                goto out;
        ret = file_update_time(file);
        if (ret < 0)
                goto out;
        if (iocb->ki_flags & IOCB_NOWAIT) {
                /* We could block if there are any pages in the range. */
                ret = -EAGAIN;
                if (filemap_range_has_page(mapping, pos, end))
                        if (filemap_invalidate_inode(inode, true, pos, end))
                                goto out;
        } else {
                ret = filemap_write_and_wait_range(mapping, pos, end);
                if (ret < 0)
                        goto out;
        }

        /*
         * After a write we want buffered reads to be sure to go to disk to get
         * the new data.  We invalidate clean cached page from the region we're
         * about to write.  We do this *before* the write so that we can return
         * without clobbering -EIOCBQUEUED from ->direct_IO().
         */
        ret = filemap_invalidate_inode(inode, true, pos, end);
        if (ret < 0)
                goto out;
        end = iocb->ki_pos + iov_iter_count(from);
        if (end > ictx->zero_point)
                ictx->zero_point = end;

        fscache_invalidate(netfs_i_cookie(ictx), NULL, i_size_read(inode),
                           FSCACHE_INVAL_DIO_WRITE);
        ret = netfs_unbuffered_write_iter_locked(iocb, from, NULL);
out:
        netfs_end_io_direct(inode);
        return ret;
}
EXPORT_SYMBOL(netfs_unbuffered_write_iter);