/* handling of writes to regular files and writing back to the server
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */
#include <linux/backing-dev.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include "internal.h"

static int afs_write_back_from_locked_page(struct afs_writeback *wb,
                                           struct page *page);

/*
 * mark a page as having been made dirty and thus needing writeback
 */
int afs_set_page_dirty(struct page *page)
{
        _enter("");
        return __set_page_dirty_nobuffers(page);
}

/*
 * unlink a writeback record because its usage has reached zero
 * - must be called with the wb->vnode->writeback_lock held
 */
static void afs_unlink_writeback(struct afs_writeback *wb)
{
        struct afs_writeback *front;
        struct afs_vnode *vnode = wb->vnode;

        list_del_init(&wb->link);
        if (!list_empty(&vnode->writebacks)) {
                /* if an fsync rises to the front of the queue then wake it
                 * up */
                front = list_entry(vnode->writebacks.next,
                                   struct afs_writeback, link);
                if (front->state == AFS_WBACK_SYNCING) {
                        _debug("wake up sync");
                        front->state = AFS_WBACK_COMPLETE;
                        wake_up(&front->waitq);
                }
        }
}

/*
 * free a writeback record
 */
static void afs_free_writeback(struct afs_writeback *wb)
{
        _enter("");
        key_put(wb->key);
        kfree(wb);
}

/*
 * dispose of a reference to a writeback record
 */
void afs_put_writeback(struct afs_writeback *wb)
{
        struct afs_vnode *vnode = wb->vnode;

        _enter("{%d}", wb->usage);

        spin_lock(&vnode->writeback_lock);
        if (--wb->usage == 0)
                afs_unlink_writeback(wb);
        else
                wb = NULL;
        spin_unlock(&vnode->writeback_lock);
        if (wb)
                afs_free_writeback(wb);
}

/*
 * partly or wholly fill a page that's under preparation for writing
 */
static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
                         loff_t pos, unsigned len, struct page *page)
{
        loff_t i_size;
        unsigned eof;
        int ret;

        _enter(",,%llu,%u", (unsigned long long)pos, len);

        ASSERTCMP(len, <=, PAGE_CACHE_SIZE);

        i_size = i_size_read(&vnode->vfs_inode);
        if (pos + len > i_size)
                eof = i_size;
        else
                eof = PAGE_CACHE_SIZE;

        ret = afs_vnode_fetch_data(vnode, key, 0, eof, page);
        if (ret < 0) {
                if (ret == -ENOENT) {
                        _debug("got NOENT from server"
                               " - marking file deleted and stale");
                        set_bit(AFS_VNODE_DELETED, &vnode->flags);
                        ret = -ESTALE;
                }
        }

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

/*
 * prepare to perform part of a write to a page
 */
int afs_write_begin(struct file *file, struct address_space *mapping,
                    loff_t pos, unsigned len, unsigned flags,
                    struct page **pagep, void **fsdata)
{
        struct afs_writeback *candidate, *wb;
        struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
        struct page *page;
        struct key *key = file->private_data;
        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
        unsigned to = from + len;
        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
        int ret;

        _enter("{%x:%u},{%lx},%u,%u",
               vnode->fid.vid, vnode->fid.vnode, index, from, to);

        candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
        if (!candidate)
                return -ENOMEM;
        candidate->vnode = vnode;
        candidate->first = candidate->last = index;
        candidate->offset_first = from;
        candidate->to_last = to;
        INIT_LIST_HEAD(&candidate->link);
        candidate->usage = 1;
        candidate->state = AFS_WBACK_PENDING;
        init_waitqueue_head(&candidate->waitq);

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page) {
                kfree(candidate);
                return -ENOMEM;
        }
        *pagep = page;
        /* page won't leak in error case: it eventually gets cleaned off LRU */

        if (!PageUptodate(page)) {
                _debug("not up to date");
                ret = afs_fill_page(vnode, key, pos, len, page);
                if (ret < 0) {
                        kfree(candidate);
                        _leave(" = %d [prep]", ret);
                        return ret;
                }
                SetPageUptodate(page);
        }

try_again:
        spin_lock(&vnode->writeback_lock);

        /* see if this page is already pending a writeback under a suitable key
         * - if so we can just join onto that one */
        wb = (struct afs_writeback *) page_private(page);
        if (wb) {
                if (wb->key == key && wb->state == AFS_WBACK_PENDING)
                        goto subsume_in_current_wb;
                goto flush_conflicting_wb;
        }

        if (index > 0) {
                /* see if we can find an already pending writeback that we can
                 * append this page to */
                list_for_each_entry(wb, &vnode->writebacks, link) {
                        if (wb->last == index - 1 && wb->key == key &&
                            wb->state == AFS_WBACK_PENDING)
                                goto append_to_previous_wb;
                }
        }

        list_add_tail(&candidate->link, &vnode->writebacks);
        candidate->key = key_get(key);
        spin_unlock(&vnode->writeback_lock);
        SetPagePrivate(page);
        set_page_private(page, (unsigned long) candidate);
        _leave(" = 0 [new]");
        return 0;

subsume_in_current_wb:
        _debug("subsume");
        ASSERTRANGE(wb->first, <=, index, <=, wb->last);
        if (index == wb->first && from < wb->offset_first)
                wb->offset_first = from;
        if (index == wb->last && to > wb->to_last)
                wb->to_last = to;
        spin_unlock(&vnode->writeback_lock);
        kfree(candidate);
        _leave(" = 0 [sub]");
        return 0;

append_to_previous_wb:
        _debug("append into %lx-%lx", wb->first, wb->last);
        wb->usage++;
        wb->last++;
        wb->to_last = to;
        spin_unlock(&vnode->writeback_lock);
        SetPagePrivate(page);
        set_page_private(page, (unsigned long) wb);
        kfree(candidate);
        _leave(" = 0 [app]");
        return 0;

        /* the page is currently bound to another context, so if it's dirty we
         * need to flush it before we can use the new context */
flush_conflicting_wb:
        _debug("flush conflict");
        if (wb->state == AFS_WBACK_PENDING)
                wb->state = AFS_WBACK_CONFLICTING;
        spin_unlock(&vnode->writeback_lock);
        if (PageDirty(page)) {
                ret = afs_write_back_from_locked_page(wb, page);
                if (ret < 0) {
                        afs_put_writeback(candidate);
                        _leave(" = %d", ret);
                        return ret;
                }
        }

        /* the page holds a ref on the writeback record */
        afs_put_writeback(wb);
        set_page_private(page, 0);
        ClearPagePrivate(page);
        goto try_again;
}

/*
 * finalise part of a write to a page
 */
int afs_write_end(struct file *file, struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned copied,
                  struct page *page, void *fsdata)
{
        struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
        loff_t i_size, maybe_i_size;

        _enter("{%x:%u},{%lx}",
               vnode->fid.vid, vnode->fid.vnode, page->index);

        maybe_i_size = pos + copied;

        i_size = i_size_read(&vnode->vfs_inode);
        if (maybe_i_size > i_size) {
                spin_lock(&vnode->writeback_lock);
                i_size = i_size_read(&vnode->vfs_inode);
                if (maybe_i_size > i_size)
                        i_size_write(&vnode->vfs_inode, maybe_i_size);
                spin_unlock(&vnode->writeback_lock);
        }

        set_page_dirty(page);
        if (PageDirty(page))
                _debug("dirtied");
        unlock_page(page);
        page_cache_release(page);

        return copied;
}

/*
 * kill all the pages in the given range
 */
static void afs_kill_pages(struct afs_vnode *vnode, bool error,
                           pgoff_t first, pgoff_t last)
{
        struct pagevec pv;
        unsigned count, loop;

        _enter("{%x:%u},%lx-%lx",
               vnode->fid.vid, vnode->fid.vnode, first, last);

        pagevec_init(&pv, 0);

        do {
                _debug("kill %lx-%lx", first, last);

                count = last - first + 1;
                if (count > PAGEVEC_SIZE)
                        count = PAGEVEC_SIZE;
                pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
                                              first, count, pv.pages);
                ASSERTCMP(pv.nr, ==, count);

                for (loop = 0; loop < count; loop++) {
                        ClearPageUptodate(pv.pages[loop]);
                        if (error)
                                SetPageError(pv.pages[loop]);
                        end_page_writeback(pv.pages[loop]);
                }

                __pagevec_release(&pv);
        } while (first < last);

        _leave("");
}

/*
 * synchronously write back the locked page and any subsequent non-locked dirty
 * pages also covered by the same writeback record
 */
static int afs_write_back_from_locked_page(struct afs_writeback *wb,
                                           struct page *primary_page)
{
        struct page *pages[8], *page;
        unsigned long count;
        unsigned n, offset, to;
        pgoff_t start, first, last;
        int loop, ret;

        _enter(",%lx", primary_page->index);

        count = 1;
        if (!clear_page_dirty_for_io(primary_page))
                BUG();
        if (test_set_page_writeback(primary_page))
                BUG();

        /* find all consecutive lockable dirty pages, stopping when we find a
         * page that is not immediately lockable, is not dirty or is missing,
         * or we reach the end of the range */
        start = primary_page->index;
        if (start >= wb->last)
                goto no_more;
        start++;
        do {
                _debug("more %lx [%lx]", start, count);
                n = wb->last - start + 1;
                if (n > ARRAY_SIZE(pages))
                        n = ARRAY_SIZE(pages);
                n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
                                          start, n, pages);
                _debug("fgpc %u", n);
                if (n == 0)
                        goto no_more;
                if (pages[0]->index != start) {
                        do {
                                put_page(pages[--n]);
                        } while (n > 0);
                        goto no_more;
                }

                for (loop = 0; loop < n; loop++) {
                        page = pages[loop];
                        if (page->index > wb->last)
                                break;
                        if (!trylock_page(page))
                                break;
                        if (!PageDirty(page) ||
                            page_private(page) != (unsigned long) wb) {
                                unlock_page(page);
                                break;
                        }
                        if (!clear_page_dirty_for_io(page))
                                BUG();
                        if (test_set_page_writeback(page))
                                BUG();
                        unlock_page(page);
                        put_page(page);
                }
                count += loop;
                if (loop < n) {
                        for (; loop < n; loop++)
                                put_page(pages[loop]);
                        goto no_more;
                }

                start += loop;
        } while (start <= wb->last && count < 65536);

no_more:
        /* we now have a contiguous set of dirty pages, each with writeback set
         * and the dirty mark cleared; the first page is locked and must remain
         * so, all the rest are unlocked */
        first = primary_page->index;
        last = first + count - 1;

        offset = (first == wb->first) ? wb->offset_first : 0;
        to = (last == wb->last) ? wb->to_last : PAGE_SIZE;

        _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);

        ret = afs_vnode_store_data(wb, first, last, offset, to);
        if (ret < 0) {
                switch (ret) {
                case -EDQUOT:
                case -ENOSPC:
                        set_bit(AS_ENOSPC,
                                &wb->vnode->vfs_inode.i_mapping->flags);
                        break;
                case -EROFS:
                case -EIO:
                case -EREMOTEIO:
                case -EFBIG:
                case -ENOENT:
                case -ENOMEDIUM:
                case -ENXIO:
                        afs_kill_pages(wb->vnode, true, first, last);
                        set_bit(AS_EIO, &wb->vnode->vfs_inode.i_mapping->flags);
                        break;
                case -EACCES:
                case -EPERM:
                case -ENOKEY:
                case -EKEYEXPIRED:
                case -EKEYREJECTED:
                case -EKEYREVOKED:
                        afs_kill_pages(wb->vnode, false, first, last);
                        break;
                default:
                        break;
                }
        } else {
                ret = count;
        }

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

/*
 * write a page back to the server
 * - the caller locked the page for us
 */
int afs_writepage(struct page *page, struct writeback_control *wbc)
{
        struct afs_writeback *wb;
        int ret;

        _enter("{%lx},", page->index);

        wb = (struct afs_writeback *) page_private(page);
        ASSERT(wb != NULL);

        ret = afs_write_back_from_locked_page(wb, page);
        unlock_page(page);
        if (ret < 0) {
                _leave(" = %d", ret);
                return 0;
        }

        wbc->nr_to_write -= ret;

        _leave(" = 0");
        return 0;
}

/*
 * write a region of pages back to the server
 */
static int afs_writepages_region(struct address_space *mapping,
                                 struct writeback_control *wbc,
                                 pgoff_t index, pgoff_t end, pgoff_t *_next)
{
        struct afs_writeback *wb;
        struct page *page;
        int ret, n;

        _enter(",,%lx,%lx,", index, end);

        do {
                n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
                                       1, &page);
                if (!n)
                        break;

                _debug("wback %lx", page->index);

                if (page->index > end) {
                        *_next = index;
                        page_cache_release(page);
                        _leave(" = 0 [%lx]", *_next);
                        return 0;
                }

                /* at this point we hold neither mapping->tree_lock nor lock on
                 * the page itself: the page may be truncated or invalidated
                 * (changing page->mapping to NULL), or even swizzled back from
                 * swapper_space to tmpfs file mapping
                 */
                lock_page(page);

                if (page->mapping != mapping) {
                        unlock_page(page);
                        page_cache_release(page);
                        continue;
                }

                if (wbc->sync_mode != WB_SYNC_NONE)
                        wait_on_page_writeback(page);

                if (PageWriteback(page) || !PageDirty(page)) {
                        unlock_page(page);
                        continue;
                }

                wb = (struct afs_writeback *) page_private(page);
                ASSERT(wb != NULL);

                spin_lock(&wb->vnode->writeback_lock);
                wb->state = AFS_WBACK_WRITING;
                spin_unlock(&wb->vnode->writeback_lock);

                ret = afs_write_back_from_locked_page(wb, page);
                unlock_page(page);
                page_cache_release(page);
                if (ret < 0) {
                        _leave(" = %d", ret);
                        return ret;
                }

                wbc->nr_to_write -= ret;

                cond_resched();
        } while (index < end && wbc->nr_to_write > 0);

        *_next = index;
        _leave(" = 0 [%lx]", *_next);
        return 0;
}

/*
 * write some of the pending data back to the server
 */
int afs_writepages(struct address_space *mapping,
                   struct writeback_control *wbc)
{
        pgoff_t start, end, next;
        int ret;

        _enter("");

        if (wbc->range_cyclic) {
                start = mapping->writeback_index;
                end = -1;
                ret = afs_writepages_region(mapping, wbc, start, end, &next);
                if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
                        ret = afs_writepages_region(mapping, wbc, 0, start,
                                                    &next);
                mapping->writeback_index = next;
        } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
                end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
                ret = afs_writepages_region(mapping, wbc, 0, end, &next);
                if (wbc->nr_to_write > 0)
                        mapping->writeback_index = next;
        } else {
                start = wbc->range_start >> PAGE_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
                ret = afs_writepages_region(mapping, wbc, start, end, &next);
        }

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

/*
 * completion of write to server
 */
void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
{
        struct afs_writeback *wb = call->wb;
        struct pagevec pv;
        unsigned count, loop;
        pgoff_t first = call->first, last = call->last;
        bool free_wb;

        _enter("{%x:%u},{%lx-%lx}",
               vnode->fid.vid, vnode->fid.vnode, first, last);

        ASSERT(wb != NULL);

        pagevec_init(&pv, 0);

        do {
                _debug("done %lx-%lx", first, last);

                count = last - first + 1;
                if (count > PAGEVEC_SIZE)
                        count = PAGEVEC_SIZE;
                pv.nr = find_get_pages_contig(call->mapping, first, count,
                                              pv.pages);
                ASSERTCMP(pv.nr, ==, count);

                spin_lock(&vnode->writeback_lock);
                for (loop = 0; loop < count; loop++) {
                        struct page *page = pv.pages[loop];
                        end_page_writeback(page);
                        if (page_private(page) == (unsigned long) wb) {
                                set_page_private(page, 0);
                                ClearPagePrivate(page);
                                wb->usage--;
                        }
                }
                free_wb = false;
                if (wb->usage == 0) {
                        afs_unlink_writeback(wb);
                        free_wb = true;
                }
                spin_unlock(&vnode->writeback_lock);
                first += count;
                if (free_wb) {
                        afs_free_writeback(wb);
                        wb = NULL;
                }

                __pagevec_release(&pv);
        } while (first <= last);

        _leave("");
}

/*
 * write to an AFS file
 */
ssize_t afs_file_write(struct kiocb *iocb, const struct iovec *iov,
                       unsigned long nr_segs, loff_t pos)
{
        struct dentry *dentry = iocb->ki_filp->f_path.dentry;
        struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
        ssize_t result;
        size_t count = iov_length(iov, nr_segs);

        _enter("{%x.%u},{%zu},%lu,",
               vnode->fid.vid, vnode->fid.vnode, count, nr_segs);

        if (IS_SWAPFILE(&vnode->vfs_inode)) {
                printk(KERN_INFO
                       "AFS: Attempt to write to active swap file!\n");
                return -EBUSY;
        }

        if (!count)
                return 0;

        result = generic_file_aio_write(iocb, iov, nr_segs, pos);
        if (IS_ERR_VALUE(result)) {
                _leave(" = %zd", result);
                return result;
        }

        _leave(" = %zd", result);
        return result;
}

/*
 * flush the vnode to the fileserver
 */
int afs_writeback_all(struct afs_vnode *vnode)
{
        struct address_space *mapping = vnode->vfs_inode.i_mapping;
        struct writeback_control wbc = {
                .sync_mode      = WB_SYNC_ALL,
                .nr_to_write    = LONG_MAX,
                .range_cyclic   = 1,
        };
        int ret;

        _enter("");

        ret = mapping->a_ops->writepages(mapping, &wbc);
        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

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

/*
 * flush any dirty pages for this process, and check for write errors.
 * - the return status from this call provides a reliable indication of
 *   whether any write errors occurred for this process.
 */
int afs_fsync(struct file *file, int datasync)
{
        struct dentry *dentry = file->f_path.dentry;
        struct afs_writeback *wb, *xwb;
        struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
        int ret;

        _enter("{%x:%u},{n=%s},%d",
               vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
               datasync);

        /* use a writeback record as a marker in the queue - when this reaches
         * the front of the queue, all the outstanding writes are either
         * completed or rejected */
        wb = kzalloc(sizeof(*wb), GFP_KERNEL);
        if (!wb)
                return -ENOMEM;
        wb->vnode = vnode;
        wb->first = 0;
        wb->last = -1;
        wb->offset_first = 0;
        wb->to_last = PAGE_SIZE;
        wb->usage = 1;
        wb->state = AFS_WBACK_SYNCING;
        init_waitqueue_head(&wb->waitq);

        spin_lock(&vnode->writeback_lock);
        list_for_each_entry(xwb, &vnode->writebacks, link) {
                if (xwb->state == AFS_WBACK_PENDING)
                        xwb->state = AFS_WBACK_CONFLICTING;
        }
        list_add_tail(&wb->link, &vnode->writebacks);
        spin_unlock(&vnode->writeback_lock);

        /* push all the outstanding writebacks to the server */
        ret = afs_writeback_all(vnode);
        if (ret < 0) {
                afs_put_writeback(wb);
                _leave(" = %d [wb]", ret);
                return ret;
        }

        /* wait for the preceding writes to actually complete */
        ret = wait_event_interruptible(wb->waitq,
                                       wb->state == AFS_WBACK_COMPLETE ||
                                       vnode->writebacks.next == &wb->link);
        afs_put_writeback(wb);
        _leave(" = %d", ret);
        return ret;
}

/*
 * notification that a previously read-only page is about to become writable
 * - if it returns an error, the caller will deliver a bus error signal
 */
int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
{
        struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);

        _enter("{{%x:%u}},{%lx}",
               vnode->fid.vid, vnode->fid.vnode, page->index);

        /* wait for the page to be written to the cache before we allow it to
         * be modified */
#ifdef CONFIG_AFS_FSCACHE
        fscache_wait_on_page_write(vnode->cache, page);
#endif

        _leave(" = 0");
        return 0;
}