write.c

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/* 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 ([email protected])
 *
 * 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, struct page *page)
{
    loff_t i_size;
    int ret;
    int len;

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

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

    ret = afs_vnode_fetch_data(vnode, key, pos, len, 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) && len != PAGE_CACHE_SIZE) {
        ret = afs_fill_page(vnode, key, index << PAGE_CACHE_SHIFT, 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, loff_t start, loff_t end, int datasync)
{
    struct dentry *dentry = file->f_path.dentry;
    struct inode *inode = file->f_mapping->host;
    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);

    ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (ret)
        return ret;
    mutex_lock(&inode->i_mutex);

    /* 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) {
        ret = -ENOMEM;
        goto out;
    }
    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);
        goto out;
    }

    /* 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);
out:
    mutex_unlock(&inode->i_mutex);
    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;
}