addr.c

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#include <linux/ceph/ceph_debug.h>

#include <linux/backing-dev.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>    /* generic_writepages */
#include <linux/slab.h>
#include <linux/pagevec.h>
#include <linux/task_io_accounting_ops.h>

#include "super.h"
#include "mds_client.h"
#include <linux/ceph/osd_client.h>

/*
 * Ceph address space ops.
 *
 * There are a few funny things going on here.
 *
 * The page->private field is used to reference a struct
 * ceph_snap_context for _every_ dirty page.  This indicates which
 * snapshot the page was logically dirtied in, and thus which snap
 * context needs to be associated with the osd write during writeback.
 *
 * Similarly, struct ceph_inode_info maintains a set of counters to
 * count dirty pages on the inode.  In the absence of snapshots,
 * i_wrbuffer_ref == i_wrbuffer_ref_head == the dirty page count.
 *
 * When a snapshot is taken (that is, when the client receives
 * notification that a snapshot was taken), each inode with caps and
 * with dirty pages (dirty pages implies there is a cap) gets a new
 * ceph_cap_snap in the i_cap_snaps list (which is sorted in ascending
 * order, new snaps go to the tail).  The i_wrbuffer_ref_head count is
 * moved to capsnap->dirty. (Unless a sync write is currently in
 * progress.  In that case, the capsnap is said to be "pending", new
 * writes cannot start, and the capsnap isn't "finalized" until the
 * write completes (or fails) and a final size/mtime for the inode for
 * that snap can be settled upon.)  i_wrbuffer_ref_head is reset to 0.
 *
 * On writeback, we must submit writes to the osd IN SNAP ORDER.  So,
 * we look for the first capsnap in i_cap_snaps and write out pages in
 * that snap context _only_.  Then we move on to the next capsnap,
 * eventually reaching the "live" or "head" context (i.e., pages that
 * are not yet snapped) and are writing the most recently dirtied
 * pages.
 *
 * Invalidate and so forth must take care to ensure the dirty page
 * accounting is preserved.
 */

#define CONGESTION_ON_THRESH(congestion_kb) (congestion_kb >> (PAGE_SHIFT-10))
#define CONGESTION_OFF_THRESH(congestion_kb)                \
    (CONGESTION_ON_THRESH(congestion_kb) -              \
     (CONGESTION_ON_THRESH(congestion_kb) >> 2))

static inline struct ceph_snap_context *page_snap_context(struct page *page)
{
    if (PagePrivate(page))
        return (void *)page->private;
    return NULL;
}

/*
 * Dirty a page.  Optimistically adjust accounting, on the assumption
 * that we won't race with invalidate.  If we do, readjust.
 */
static int ceph_set_page_dirty(struct page *page)
{
    struct address_space *mapping = page->mapping;
    struct inode *inode;
    struct ceph_inode_info *ci;
    int undo = 0;
    struct ceph_snap_context *snapc;

    if (unlikely(!mapping))
        return !TestSetPageDirty(page);

    if (TestSetPageDirty(page)) {
        dout("%p set_page_dirty %p idx %lu -- already dirty\n",
             mapping->host, page, page->index);
        return 0;
    }

    inode = mapping->host;
    ci = ceph_inode(inode);

    /*
     * Note that we're grabbing a snapc ref here without holding
     * any locks!
     */
    snapc = ceph_get_snap_context(ci->i_snap_realm->cached_context);

    /* dirty the head */
    spin_lock(&ci->i_ceph_lock);
    if (ci->i_head_snapc == NULL)
        ci->i_head_snapc = ceph_get_snap_context(snapc);
    ++ci->i_wrbuffer_ref_head;
    if (ci->i_wrbuffer_ref == 0)
        ihold(inode);
    ++ci->i_wrbuffer_ref;
    dout("%p set_page_dirty %p idx %lu head %d/%d -> %d/%d "
         "snapc %p seq %lld (%d snaps)\n",
         mapping->host, page, page->index,
         ci->i_wrbuffer_ref-1, ci->i_wrbuffer_ref_head-1,
         ci->i_wrbuffer_ref, ci->i_wrbuffer_ref_head,
         snapc, snapc->seq, snapc->num_snaps);
    spin_unlock(&ci->i_ceph_lock);

    /* now adjust page */
    spin_lock_irq(&mapping->tree_lock);
    if (page->mapping) {    /* Race with truncate? */
        WARN_ON_ONCE(!PageUptodate(page));
        account_page_dirtied(page, page->mapping);
        radix_tree_tag_set(&mapping->page_tree,
                page_index(page), PAGECACHE_TAG_DIRTY);

        /*
         * Reference snap context in page->private.  Also set
         * PagePrivate so that we get invalidatepage callback.
         */
        page->private = (unsigned long)snapc;
        SetPagePrivate(page);
    } else {
        dout("ANON set_page_dirty %p (raced truncate?)\n", page);
        undo = 1;
    }

    spin_unlock_irq(&mapping->tree_lock);

    if (undo)
        /* whoops, we failed to dirty the page */
        ceph_put_wrbuffer_cap_refs(ci, 1, snapc);

    __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

    BUG_ON(!PageDirty(page));
    return 1;
}

/*
 * If we are truncating the full page (i.e. offset == 0), adjust the
 * dirty page counters appropriately.  Only called if there is private
 * data on the page.
 */
static void ceph_invalidatepage(struct page *page, unsigned long offset)
{
    struct inode *inode;
    struct ceph_inode_info *ci;
    struct ceph_snap_context *snapc = page_snap_context(page);

    BUG_ON(!PageLocked(page));
    BUG_ON(!PagePrivate(page));
    BUG_ON(!page->mapping);

    inode = page->mapping->host;

    /*
     * We can get non-dirty pages here due to races between
     * set_page_dirty and truncate_complete_page; just spit out a
     * warning, in case we end up with accounting problems later.
     */
    if (!PageDirty(page))
        pr_err("%p invalidatepage %p page not dirty\n", inode, page);

    if (offset == 0)
        ClearPageChecked(page);

    ci = ceph_inode(inode);
    if (offset == 0) {
        dout("%p invalidatepage %p idx %lu full dirty page %lu\n",
             inode, page, page->index, offset);
        ceph_put_wrbuffer_cap_refs(ci, 1, snapc);
        ceph_put_snap_context(snapc);
        page->private = 0;
        ClearPagePrivate(page);
    } else {
        dout("%p invalidatepage %p idx %lu partial dirty page\n",
             inode, page, page->index);
    }
}

/* just a sanity check */
static int ceph_releasepage(struct page *page, gfp_t g)
{
    struct inode *inode = page->mapping ? page->mapping->host : NULL;
    dout("%p releasepage %p idx %lu\n", inode, page, page->index);
    WARN_ON(PageDirty(page));
    WARN_ON(PagePrivate(page));
    return 0;
}

/*
 * read a single page, without unlocking it.
 */
static int readpage_nounlock(struct file *filp, struct page *page)
{
    struct inode *inode = filp->f_dentry->d_inode;
    struct ceph_inode_info *ci = ceph_inode(inode);
    struct ceph_osd_client *osdc = 
        &ceph_inode_to_client(inode)->client->osdc;
    int err = 0;
    u64 len = PAGE_CACHE_SIZE;

    dout("readpage inode %p file %p page %p index %lu\n",
         inode, filp, page, page->index);
    err = ceph_osdc_readpages(osdc, ceph_vino(inode), &ci->i_layout,
                  (u64) page_offset(page), &len,
                  ci->i_truncate_seq, ci->i_truncate_size,
                  &page, 1, 0);
    if (err == -ENOENT)
        err = 0;
    if (err < 0) {
        SetPageError(page);
        goto out;
    } else if (err < PAGE_CACHE_SIZE) {
        /* zero fill remainder of page */
        zero_user_segment(page, err, PAGE_CACHE_SIZE);
    }
    SetPageUptodate(page);

out:
    return err < 0 ? err : 0;
}

static int ceph_readpage(struct file *filp, struct page *page)
{
    int r = readpage_nounlock(filp, page);
    unlock_page(page);
    return r;
}

/*
 * Finish an async read(ahead) op.
 */
static void finish_read(struct ceph_osd_request *req, struct ceph_msg *msg)
{
    struct inode *inode = req->r_inode;
    struct ceph_osd_reply_head *replyhead;
    int rc, bytes;
    int i;

    /* parse reply */
    replyhead = msg->front.iov_base;
    WARN_ON(le32_to_cpu(replyhead->num_ops) == 0);
    rc = le32_to_cpu(replyhead->result);
    bytes = le32_to_cpu(msg->hdr.data_len);

    dout("finish_read %p req %p rc %d bytes %d\n", inode, req, rc, bytes);

    /* unlock all pages, zeroing any data we didn't read */
    for (i = 0; i < req->r_num_pages; i++, bytes -= PAGE_CACHE_SIZE) {
        struct page *page = req->r_pages[i];

        if (bytes < (int)PAGE_CACHE_SIZE) {
            /* zero (remainder of) page */
            int s = bytes < 0 ? 0 : bytes;
            zero_user_segment(page, s, PAGE_CACHE_SIZE);
        }
        dout("finish_read %p uptodate %p idx %lu\n", inode, page,
             page->index);
        flush_dcache_page(page);
        SetPageUptodate(page);
        unlock_page(page);
        page_cache_release(page);
    }
    kfree(req->r_pages);
}

/*
 * start an async read(ahead) operation.  return nr_pages we submitted
 * a read for on success, or negative error code.
 */
static int start_read(struct inode *inode, struct list_head *page_list, int max)
{
    struct ceph_osd_client *osdc =
        &ceph_inode_to_client(inode)->client->osdc;
    struct ceph_inode_info *ci = ceph_inode(inode);
    struct page *page = list_entry(page_list->prev, struct page, lru);
    struct ceph_osd_request *req;
    u64 off;
    u64 len;
    int i;
    struct page **pages;
    pgoff_t next_index;
    int nr_pages = 0;
    int ret;

    off = (u64) page_offset(page);

    /* count pages */
    next_index = page->index;
    list_for_each_entry_reverse(page, page_list, lru) {
        if (page->index != next_index)
            break;
        nr_pages++;
        next_index++;
        if (max && nr_pages == max)
            break;
    }
    len = nr_pages << PAGE_CACHE_SHIFT;
    dout("start_read %p nr_pages %d is %lld~%lld\n", inode, nr_pages,
         off, len);

    req = ceph_osdc_new_request(osdc, &ci->i_layout, ceph_vino(inode),
                    off, &len,
                    CEPH_OSD_OP_READ, CEPH_OSD_FLAG_READ,
                    NULL, 0,
                    ci->i_truncate_seq, ci->i_truncate_size,
                    NULL, false, 1, 0);
    if (IS_ERR(req))
        return PTR_ERR(req);

    /* build page vector */
    nr_pages = len >> PAGE_CACHE_SHIFT;
    pages = kmalloc(sizeof(*pages) * nr_pages, GFP_NOFS);
    ret = -ENOMEM;
    if (!pages)
        goto out;
    for (i = 0; i < nr_pages; ++i) {
        page = list_entry(page_list->prev, struct page, lru);
        BUG_ON(PageLocked(page));
        list_del(&page->lru);
        
        dout("start_read %p adding %p idx %lu\n", inode, page,
             page->index);
        if (add_to_page_cache_lru(page, &inode->i_data, page->index,
                      GFP_NOFS)) {
            page_cache_release(page);
            dout("start_read %p add_to_page_cache failed %p\n",
                 inode, page);
            nr_pages = i;
            goto out_pages;
        }
        pages[i] = page;
    }
    req->r_pages = pages;
    req->r_num_pages = nr_pages;
    req->r_callback = finish_read;
    req->r_inode = inode;

    dout("start_read %p starting %p %lld~%lld\n", inode, req, off, len);
    ret = ceph_osdc_start_request(osdc, req, false);
    if (ret < 0)
        goto out_pages;
    ceph_osdc_put_request(req);
    return nr_pages;

out_pages:
    ceph_release_page_vector(pages, nr_pages);
out:
    ceph_osdc_put_request(req);
    return ret;
}


/*
 * Read multiple pages.  Leave pages we don't read + unlock in page_list;
 * the caller (VM) cleans them up.
 */
static int ceph_readpages(struct file *file, struct address_space *mapping,
              struct list_head *page_list, unsigned nr_pages)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
    int rc = 0;
    int max = 0;

    if (fsc->mount_options->rsize >= PAGE_CACHE_SIZE)
        max = (fsc->mount_options->rsize + PAGE_CACHE_SIZE - 1)
            >> PAGE_SHIFT;

    dout("readpages %p file %p nr_pages %d max %d\n", inode, file, nr_pages,
         max);
    while (!list_empty(page_list)) {
        rc = start_read(inode, page_list, max);
        if (rc < 0)
            goto out;
        BUG_ON(rc == 0);
    }
out:
    dout("readpages %p file %p ret %d\n", inode, file, rc);
    return rc;
}

/*
 * Get ref for the oldest snapc for an inode with dirty data... that is, the
 * only snap context we are allowed to write back.
 */
static struct ceph_snap_context *get_oldest_context(struct inode *inode,
                            u64 *snap_size)
{
    struct ceph_inode_info *ci = ceph_inode(inode);
    struct ceph_snap_context *snapc = NULL;
    struct ceph_cap_snap *capsnap = NULL;

    spin_lock(&ci->i_ceph_lock);
    list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
        dout(" cap_snap %p snapc %p has %d dirty pages\n", capsnap,
             capsnap->context, capsnap->dirty_pages);
        if (capsnap->dirty_pages) {
            snapc = ceph_get_snap_context(capsnap->context);
            if (snap_size)
                *snap_size = capsnap->size;
            break;
        }
    }
    if (!snapc && ci->i_wrbuffer_ref_head) {
        snapc = ceph_get_snap_context(ci->i_head_snapc);
        dout(" head snapc %p has %d dirty pages\n",
             snapc, ci->i_wrbuffer_ref_head);
    }
    spin_unlock(&ci->i_ceph_lock);
    return snapc;
}

/*
 * Write a single page, but leave the page locked.
 *
 * If we get a write error, set the page error bit, but still adjust the
 * dirty page accounting (i.e., page is no longer dirty).
 */
static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
{
    struct inode *inode;
    struct ceph_inode_info *ci;
    struct ceph_fs_client *fsc;
    struct ceph_osd_client *osdc;
    loff_t page_off = page_offset(page);
    int len = PAGE_CACHE_SIZE;
    loff_t i_size;
    int err = 0;
    struct ceph_snap_context *snapc, *oldest;
    u64 snap_size = 0;
    long writeback_stat;

    dout("writepage %p idx %lu\n", page, page->index);

    if (!page->mapping || !page->mapping->host) {
        dout("writepage %p - no mapping\n", page);
        return -EFAULT;
    }
    inode = page->mapping->host;
    ci = ceph_inode(inode);
    fsc = ceph_inode_to_client(inode);
    osdc = &fsc->client->osdc;

    /* verify this is a writeable snap context */
    snapc = page_snap_context(page);
    if (snapc == NULL) {
        dout("writepage %p page %p not dirty?\n", inode, page);
        goto out;
    }
    oldest = get_oldest_context(inode, &snap_size);
    if (snapc->seq > oldest->seq) {
        dout("writepage %p page %p snapc %p not writeable - noop\n",
             inode, page, snapc);
        /* we should only noop if called by kswapd */
        WARN_ON((current->flags & PF_MEMALLOC) == 0);
        ceph_put_snap_context(oldest);
        goto out;
    }
    ceph_put_snap_context(oldest);

    /* is this a partial page at end of file? */
    if (snap_size)
        i_size = snap_size;
    else
        i_size = i_size_read(inode);
    if (i_size < page_off + len)
        len = i_size - page_off;

    dout("writepage %p page %p index %lu on %llu~%u snapc %p\n",
         inode, page, page->index, page_off, len, snapc);

    writeback_stat = atomic_long_inc_return(&fsc->writeback_count);
    if (writeback_stat >
        CONGESTION_ON_THRESH(fsc->mount_options->congestion_kb))
        set_bdi_congested(&fsc->backing_dev_info, BLK_RW_ASYNC);

    set_page_writeback(page);
    err = ceph_osdc_writepages(osdc, ceph_vino(inode),
                   &ci->i_layout, snapc,
                   page_off, len,
                   ci->i_truncate_seq, ci->i_truncate_size,
                   &inode->i_mtime,
                   &page, 1, 0, 0, true);
    if (err < 0) {
        dout("writepage setting page/mapping error %d %p\n", err, page);
        SetPageError(page);
        mapping_set_error(&inode->i_data, err);
        if (wbc)
            wbc->pages_skipped++;
    } else {
        dout("writepage cleaned page %p\n", page);
        err = 0;  /* vfs expects us to return 0 */
    }
    page->private = 0;
    ClearPagePrivate(page);
    end_page_writeback(page);
    ceph_put_wrbuffer_cap_refs(ci, 1, snapc);
    ceph_put_snap_context(snapc);  /* page's reference */
out:
    return err;
}

static int ceph_writepage(struct page *page, struct writeback_control *wbc)
{
    int err;
    struct inode *inode = page->mapping->host;
    BUG_ON(!inode);
    ihold(inode);
    err = writepage_nounlock(page, wbc);
    unlock_page(page);
    iput(inode);
    return err;
}


/*
 * lame release_pages helper.  release_pages() isn't exported to
 * modules.
 */
static void ceph_release_pages(struct page **pages, int num)
{
    struct pagevec pvec;
    int i;

    pagevec_init(&pvec, 0);
    for (i = 0; i < num; i++) {
        if (pagevec_add(&pvec, pages[i]) == 0)
            pagevec_release(&pvec);
    }
    pagevec_release(&pvec);
}


/*
 * async writeback completion handler.
 *
 * If we get an error, set the mapping error bit, but not the individual
 * page error bits.
 */
static void writepages_finish(struct ceph_osd_request *req,
                  struct ceph_msg *msg)
{
    struct inode *inode = req->r_inode;
    struct ceph_osd_reply_head *replyhead;
    struct ceph_osd_op *op;
    struct ceph_inode_info *ci = ceph_inode(inode);
    unsigned wrote;
    struct page *page;
    int i;
    struct ceph_snap_context *snapc = req->r_snapc;
    struct address_space *mapping = inode->i_mapping;
    __s32 rc = -EIO;
    u64 bytes = 0;
    struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
    long writeback_stat;
    unsigned issued = ceph_caps_issued(ci);

    /* parse reply */
    replyhead = msg->front.iov_base;
    WARN_ON(le32_to_cpu(replyhead->num_ops) == 0);
    op = (void *)(replyhead + 1);
    rc = le32_to_cpu(replyhead->result);
    bytes = le64_to_cpu(op->extent.length);

    if (rc >= 0) {
        /*
         * Assume we wrote the pages we originally sent.  The
         * osd might reply with fewer pages if our writeback
         * raced with a truncation and was adjusted at the osd,
         * so don't believe the reply.
         */
        wrote = req->r_num_pages;
    } else {
        wrote = 0;
        mapping_set_error(mapping, rc);
    }
    dout("writepages_finish %p rc %d bytes %llu wrote %d (pages)\n",
         inode, rc, bytes, wrote);

    /* clean all pages */
    for (i = 0; i < req->r_num_pages; i++) {
        page = req->r_pages[i];
        BUG_ON(!page);
        WARN_ON(!PageUptodate(page));

        writeback_stat =
            atomic_long_dec_return(&fsc->writeback_count);
        if (writeback_stat <
            CONGESTION_OFF_THRESH(fsc->mount_options->congestion_kb))
            clear_bdi_congested(&fsc->backing_dev_info,
                        BLK_RW_ASYNC);

        ceph_put_snap_context(page_snap_context(page));
        page->private = 0;
        ClearPagePrivate(page);
        dout("unlocking %d %p\n", i, page);
        end_page_writeback(page);

        /*
         * We lost the cache cap, need to truncate the page before
         * it is unlocked, otherwise we'd truncate it later in the
         * page truncation thread, possibly losing some data that
         * raced its way in
         */
        if ((issued & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0)
            generic_error_remove_page(inode->i_mapping, page);

        unlock_page(page);
    }
    dout("%p wrote+cleaned %d pages\n", inode, wrote);
    ceph_put_wrbuffer_cap_refs(ci, req->r_num_pages, snapc);

    ceph_release_pages(req->r_pages, req->r_num_pages);
    if (req->r_pages_from_pool)
        mempool_free(req->r_pages,
                 ceph_sb_to_client(inode->i_sb)->wb_pagevec_pool);
    else
        kfree(req->r_pages);
    ceph_osdc_put_request(req);
}

/*
 * allocate a page vec, either directly, or if necessary, via a the
 * mempool.  we avoid the mempool if we can because req->r_num_pages
 * may be less than the maximum write size.
 */
static void alloc_page_vec(struct ceph_fs_client *fsc,
               struct ceph_osd_request *req)
{
    req->r_pages = kmalloc(sizeof(struct page *) * req->r_num_pages,
                   GFP_NOFS);
    if (!req->r_pages) {
        req->r_pages = mempool_alloc(fsc->wb_pagevec_pool, GFP_NOFS);
        req->r_pages_from_pool = 1;
        WARN_ON(!req->r_pages);
    }
}

/*
 * initiate async writeback
 */
static int ceph_writepages_start(struct address_space *mapping,
                 struct writeback_control *wbc)
{
    struct inode *inode = mapping->host;
    struct ceph_inode_info *ci = ceph_inode(inode);
    struct ceph_fs_client *fsc;
    pgoff_t index, start, end;
    int range_whole = 0;
    int should_loop = 1;
    pgoff_t max_pages = 0, max_pages_ever = 0;
    struct ceph_snap_context *snapc = NULL, *last_snapc = NULL, *pgsnapc;
    struct pagevec pvec;
    int done = 0;
    int rc = 0;
    unsigned wsize = 1 << inode->i_blkbits;
    struct ceph_osd_request *req = NULL;
    int do_sync;
    u64 snap_size = 0;

    /*
     * Include a 'sync' in the OSD request if this is a data
     * integrity write (e.g., O_SYNC write or fsync()), or if our
     * cap is being revoked.
     */
    do_sync = wbc->sync_mode == WB_SYNC_ALL;
    if (ceph_caps_revoking(ci, CEPH_CAP_FILE_BUFFER))
        do_sync = 1;
    dout("writepages_start %p dosync=%d (mode=%s)\n",
         inode, do_sync,
         wbc->sync_mode == WB_SYNC_NONE ? "NONE" :
         (wbc->sync_mode == WB_SYNC_ALL ? "ALL" : "HOLD"));

    fsc = ceph_inode_to_client(inode);
    if (fsc->mount_state == CEPH_MOUNT_SHUTDOWN) {
        pr_warning("writepage_start %p on forced umount\n", inode);
        return -EIO; /* we're in a forced umount, don't write! */
    }
    if (fsc->mount_options->wsize && fsc->mount_options->wsize < wsize)
        wsize = fsc->mount_options->wsize;
    if (wsize < PAGE_CACHE_SIZE)
        wsize = PAGE_CACHE_SIZE;
    max_pages_ever = wsize >> PAGE_CACHE_SHIFT;

    pagevec_init(&pvec, 0);

    /* where to start/end? */
    if (wbc->range_cyclic) {
        start = mapping->writeback_index; /* Start from prev offset */
        end = -1;
        dout(" cyclic, start at %lu\n", start);
    } else {
        start = wbc->range_start >> PAGE_CACHE_SHIFT;
        end = wbc->range_end >> PAGE_CACHE_SHIFT;
        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
            range_whole = 1;
        should_loop = 0;
        dout(" not cyclic, %lu to %lu\n", start, end);
    }
    index = start;

retry:
    /* find oldest snap context with dirty data */
    ceph_put_snap_context(snapc);
    snapc = get_oldest_context(inode, &snap_size);
    if (!snapc) {
        /* hmm, why does writepages get called when there
           is no dirty data? */
        dout(" no snap context with dirty data?\n");
        goto out;
    }
    dout(" oldest snapc is %p seq %lld (%d snaps)\n",
         snapc, snapc->seq, snapc->num_snaps);
    if (last_snapc && snapc != last_snapc) {
        /* if we switched to a newer snapc, restart our scan at the
         * start of the original file range. */
        dout("  snapc differs from last pass, restarting at %lu\n",
             index);
        index = start;
    }
    last_snapc = snapc;

    while (!done && index <= end) {
        unsigned i;
        int first;
        pgoff_t next;
        int pvec_pages, locked_pages;
        struct page *page;
        int want;
        u64 offset, len;
        struct ceph_osd_request_head *reqhead;
        struct ceph_osd_op *op;
        long writeback_stat;

        next = 0;
        locked_pages = 0;
        max_pages = max_pages_ever;

get_more_pages:
        first = -1;
        want = min(end - index,
               min((pgoff_t)PAGEVEC_SIZE,
                   max_pages - (pgoff_t)locked_pages) - 1)
            + 1;
        pvec_pages = pagevec_lookup_tag(&pvec, mapping, &index,
                        PAGECACHE_TAG_DIRTY,
                        want);
        dout("pagevec_lookup_tag got %d\n", pvec_pages);
        if (!pvec_pages && !locked_pages)
            break;
        for (i = 0; i < pvec_pages && locked_pages < max_pages; i++) {
            page = pvec.pages[i];
            dout("? %p idx %lu\n", page, page->index);
            if (locked_pages == 0)
                lock_page(page);  /* first page */
            else if (!trylock_page(page))
                break;

            /* only dirty pages, or our accounting breaks */
            if (unlikely(!PageDirty(page)) ||
                unlikely(page->mapping != mapping)) {
                dout("!dirty or !mapping %p\n", page);
                unlock_page(page);
                break;
            }
            if (!wbc->range_cyclic && page->index > end) {
                dout("end of range %p\n", page);
                done = 1;
                unlock_page(page);
                break;
            }
            if (next && (page->index != next)) {
                dout("not consecutive %p\n", page);
                unlock_page(page);
                break;
            }
            if (wbc->sync_mode != WB_SYNC_NONE) {
                dout("waiting on writeback %p\n", page);
                wait_on_page_writeback(page);
            }
            if ((snap_size && page_offset(page) > snap_size) ||
                (!snap_size &&
                 page_offset(page) > i_size_read(inode))) {
                dout("%p page eof %llu\n", page, snap_size ?
                     snap_size : i_size_read(inode));
                done = 1;
                unlock_page(page);
                break;
            }
            if (PageWriteback(page)) {
                dout("%p under writeback\n", page);
                unlock_page(page);
                break;
            }

            /* only if matching snap context */
            pgsnapc = page_snap_context(page);
            if (pgsnapc->seq > snapc->seq) {
                dout("page snapc %p %lld > oldest %p %lld\n",
                     pgsnapc, pgsnapc->seq, snapc, snapc->seq);
                unlock_page(page);
                if (!locked_pages)
                    continue; /* keep looking for snap */
                break;
            }

            if (!clear_page_dirty_for_io(page)) {
                dout("%p !clear_page_dirty_for_io\n", page);
                unlock_page(page);
                break;
            }

            /* ok */
            if (locked_pages == 0) {
                /* prepare async write request */
                offset = (u64) page_offset(page);
                len = wsize;
                req = ceph_osdc_new_request(&fsc->client->osdc,
                        &ci->i_layout,
                        ceph_vino(inode),
                        offset, &len,
                        CEPH_OSD_OP_WRITE,
                        CEPH_OSD_FLAG_WRITE |
                            CEPH_OSD_FLAG_ONDISK,
                        snapc, do_sync,
                        ci->i_truncate_seq,
                        ci->i_truncate_size,
                        &inode->i_mtime, true, 1, 0);

                if (IS_ERR(req)) {
                    rc = PTR_ERR(req);
                    unlock_page(page);
                    break;
                }

                max_pages = req->r_num_pages;

                alloc_page_vec(fsc, req);
                req->r_callback = writepages_finish;
                req->r_inode = inode;
            }

            /* note position of first page in pvec */
            if (first < 0)
                first = i;
            dout("%p will write page %p idx %lu\n",
                 inode, page, page->index);

            writeback_stat =
                   atomic_long_inc_return(&fsc->writeback_count);
            if (writeback_stat > CONGESTION_ON_THRESH(
                    fsc->mount_options->congestion_kb)) {
                set_bdi_congested(&fsc->backing_dev_info,
                          BLK_RW_ASYNC);
            }

            set_page_writeback(page);
            req->r_pages[locked_pages] = page;
            locked_pages++;
            next = page->index + 1;
        }

        /* did we get anything? */
        if (!locked_pages)
            goto release_pvec_pages;
        if (i) {
            int j;
            BUG_ON(!locked_pages || first < 0);

            if (pvec_pages && i == pvec_pages &&
                locked_pages < max_pages) {
                dout("reached end pvec, trying for more\n");
                pagevec_reinit(&pvec);
                goto get_more_pages;
            }

            /* shift unused pages over in the pvec...  we
             * will need to release them below. */
            for (j = i; j < pvec_pages; j++) {
                dout(" pvec leftover page %p\n",
                     pvec.pages[j]);
                pvec.pages[j-i+first] = pvec.pages[j];
            }
            pvec.nr -= i-first;
        }

        /* submit the write */
        offset = req->r_pages[0]->index << PAGE_CACHE_SHIFT;
        len = min((snap_size ? snap_size : i_size_read(inode)) - offset,
              (u64)locked_pages << PAGE_CACHE_SHIFT);
        dout("writepages got %d pages at %llu~%llu\n",
             locked_pages, offset, len);

        /* revise final length, page count */
        req->r_num_pages = locked_pages;
        reqhead = req->r_request->front.iov_base;
        op = (void *)(reqhead + 1);
        op->extent.length = cpu_to_le64(len);
        op->payload_len = cpu_to_le32(len);
        req->r_request->hdr.data_len = cpu_to_le32(len);

        rc = ceph_osdc_start_request(&fsc->client->osdc, req, true);
        BUG_ON(rc);
        req = NULL;

        /* continue? */
        index = next;
        wbc->nr_to_write -= locked_pages;
        if (wbc->nr_to_write <= 0)
            done = 1;

release_pvec_pages:
        dout("pagevec_release on %d pages (%p)\n", (int)pvec.nr,
             pvec.nr ? pvec.pages[0] : NULL);
        pagevec_release(&pvec);

        if (locked_pages && !done)
            goto retry;
    }

    if (should_loop && !done) {
        /* more to do; loop back to beginning of file */
        dout("writepages looping back to beginning of file\n");
        should_loop = 0;
        index = 0;
        goto retry;
    }

    if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
        mapping->writeback_index = index;

out:
    if (req)
        ceph_osdc_put_request(req);
    ceph_put_snap_context(snapc);
    dout("writepages done, rc = %d\n", rc);
    return rc;
}



/*
 * See if a given @snapc is either writeable, or already written.
 */
static int context_is_writeable_or_written(struct inode *inode,
                       struct ceph_snap_context *snapc)
{
    struct ceph_snap_context *oldest = get_oldest_context(inode, NULL);
    int ret = !oldest || snapc->seq <= oldest->seq;

    ceph_put_snap_context(oldest);
    return ret;
}

/*
 * We are only allowed to write into/dirty the page if the page is
 * clean, or already dirty within the same snap context.
 *
 * called with page locked.
 * return success with page locked,
 * or any failure (incl -EAGAIN) with page unlocked.
 */
static int ceph_update_writeable_page(struct file *file,
                loff_t pos, unsigned len,
                struct page *page)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct ceph_inode_info *ci = ceph_inode(inode);
    struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
    loff_t page_off = pos & PAGE_CACHE_MASK;
    int pos_in_page = pos & ~PAGE_CACHE_MASK;
    int end_in_page = pos_in_page + len;
    loff_t i_size;
    int r;
    struct ceph_snap_context *snapc, *oldest;

retry_locked:
    /* writepages currently holds page lock, but if we change that later, */
    wait_on_page_writeback(page);

    /* check snap context */
    BUG_ON(!ci->i_snap_realm);
    down_read(&mdsc->snap_rwsem);
    BUG_ON(!ci->i_snap_realm->cached_context);
    snapc = page_snap_context(page);
    if (snapc && snapc != ci->i_head_snapc) {
        /*
         * this page is already dirty in another (older) snap
         * context!  is it writeable now?
         */
        oldest = get_oldest_context(inode, NULL);
        up_read(&mdsc->snap_rwsem);

        if (snapc->seq > oldest->seq) {
            ceph_put_snap_context(oldest);
            dout(" page %p snapc %p not current or oldest\n",
                 page, snapc);
            /*
             * queue for writeback, and wait for snapc to
             * be writeable or written
             */
            snapc = ceph_get_snap_context(snapc);
            unlock_page(page);
            ceph_queue_writeback(inode);
            r = wait_event_interruptible(ci->i_cap_wq,
                   context_is_writeable_or_written(inode, snapc));
            ceph_put_snap_context(snapc);
            if (r == -ERESTARTSYS)
                return r;
            return -EAGAIN;
        }
        ceph_put_snap_context(oldest);

        /* yay, writeable, do it now (without dropping page lock) */
        dout(" page %p snapc %p not current, but oldest\n",
             page, snapc);
        if (!clear_page_dirty_for_io(page))
            goto retry_locked;
        r = writepage_nounlock(page, NULL);
        if (r < 0)
            goto fail_nosnap;
        goto retry_locked;
    }

    if (PageUptodate(page)) {
        dout(" page %p already uptodate\n", page);
        return 0;
    }

    /* full page? */
    if (pos_in_page == 0 && len == PAGE_CACHE_SIZE)
        return 0;

    /* past end of file? */
    i_size = inode->i_size;   /* caller holds i_mutex */

    if (i_size + len > inode->i_sb->s_maxbytes) {
        /* file is too big */
        r = -EINVAL;
        goto fail;
    }

    if (page_off >= i_size ||
        (pos_in_page == 0 && (pos+len) >= i_size &&
         end_in_page - pos_in_page != PAGE_CACHE_SIZE)) {
        dout(" zeroing %p 0 - %d and %d - %d\n",
             page, pos_in_page, end_in_page, (int)PAGE_CACHE_SIZE);
        zero_user_segments(page,
                   0, pos_in_page,
                   end_in_page, PAGE_CACHE_SIZE);
        return 0;
    }

    /* we need to read it. */
    up_read(&mdsc->snap_rwsem);
    r = readpage_nounlock(file, page);
    if (r < 0)
        goto fail_nosnap;
    goto retry_locked;

fail:
    up_read(&mdsc->snap_rwsem);
fail_nosnap:
    unlock_page(page);
    return r;
}

/*
 * We are only allowed to write into/dirty the page if the page is
 * clean, or already dirty within the same snap context.
 */
static int ceph_write_begin(struct file *file, struct address_space *mapping,
                loff_t pos, unsigned len, unsigned flags,
                struct page **pagep, void **fsdata)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct page *page;
    pgoff_t index = pos >> PAGE_CACHE_SHIFT;
    int r;

    do {
        /* get a page */
        page = grab_cache_page_write_begin(mapping, index, 0);
        if (!page)
            return -ENOMEM;
        *pagep = page;

        dout("write_begin file %p inode %p page %p %d~%d\n", file,
             inode, page, (int)pos, (int)len);

        r = ceph_update_writeable_page(file, pos, len, page);
    } while (r == -EAGAIN);

    return r;
}

/*
 * we don't do anything in here that simple_write_end doesn't do
 * except adjust dirty page accounting and drop read lock on
 * mdsc->snap_rwsem.
 */
static int ceph_write_end(struct file *file, struct address_space *mapping,
              loff_t pos, unsigned len, unsigned copied,
              struct page *page, void *fsdata)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
    struct ceph_mds_client *mdsc = fsc->mdsc;
    unsigned from = pos & (PAGE_CACHE_SIZE - 1);
    int check_cap = 0;

    dout("write_end file %p inode %p page %p %d~%d (%d)\n", file,
         inode, page, (int)pos, (int)copied, (int)len);

    /* zero the stale part of the page if we did a short copy */
    if (copied < len)
        zero_user_segment(page, from+copied, len);

    /* did file size increase? */
    /* (no need for i_size_read(); we caller holds i_mutex */
    if (pos+copied > inode->i_size)
        check_cap = ceph_inode_set_size(inode, pos+copied);

    if (!PageUptodate(page))
        SetPageUptodate(page);

    set_page_dirty(page);

    unlock_page(page);
    up_read(&mdsc->snap_rwsem);
    page_cache_release(page);

    if (check_cap)
        ceph_check_caps(ceph_inode(inode), CHECK_CAPS_AUTHONLY, NULL);

    return copied;
}

/*
 * we set .direct_IO to indicate direct io is supported, but since we
 * intercept O_DIRECT reads and writes early, this function should
 * never get called.
 */
static ssize_t ceph_direct_io(int rw, struct kiocb *iocb,
                  const struct iovec *iov,
                  loff_t pos, unsigned long nr_segs)
{
    WARN_ON(1);
    return -EINVAL;
}

const struct address_space_operations ceph_aops = {
    .readpage = ceph_readpage,
    .readpages = ceph_readpages,
    .writepage = ceph_writepage,
    .writepages = ceph_writepages_start,
    .write_begin = ceph_write_begin,
    .write_end = ceph_write_end,
    .set_page_dirty = ceph_set_page_dirty,
    .invalidatepage = ceph_invalidatepage,
    .releasepage = ceph_releasepage,
    .direct_IO = ceph_direct_io,
};


/*
 * vm ops
 */

/*
 * Reuse write_begin here for simplicity.
 */
static int ceph_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
    struct inode *inode = vma->vm_file->f_dentry->d_inode;
    struct page *page = vmf->page;
    struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
    loff_t off = page_offset(page);
    loff_t size, len;
    int ret;

    /* Update time before taking page lock */
    file_update_time(vma->vm_file);

    size = i_size_read(inode);
    if (off + PAGE_CACHE_SIZE <= size)
        len = PAGE_CACHE_SIZE;
    else
        len = size & ~PAGE_CACHE_MASK;

    dout("page_mkwrite %p %llu~%llu page %p idx %lu\n", inode,
         off, len, page, page->index);

    lock_page(page);

    ret = VM_FAULT_NOPAGE;
    if ((off > size) ||
        (page->mapping != inode->i_mapping))
        goto out;

    ret = ceph_update_writeable_page(vma->vm_file, off, len, page);
    if (ret == 0) {
        /* success.  we'll keep the page locked. */
        set_page_dirty(page);
        up_read(&mdsc->snap_rwsem);
        ret = VM_FAULT_LOCKED;
    } else {
        if (ret == -ENOMEM)
            ret = VM_FAULT_OOM;
        else
            ret = VM_FAULT_SIGBUS;
    }
out:
    dout("page_mkwrite %p %llu~%llu = %d\n", inode, off, len, ret);
    if (ret != VM_FAULT_LOCKED)
        unlock_page(page);
    return ret;
}

static struct vm_operations_struct ceph_vmops = {
    .fault      = filemap_fault,
    .page_mkwrite   = ceph_page_mkwrite,
    .remap_pages    = generic_file_remap_pages,
};

int ceph_mmap(struct file *file, struct vm_area_struct *vma)
{
    struct address_space *mapping = file->f_mapping;

    if (!mapping->a_ops->readpage)
        return -ENOEXEC;
    file_accessed(file);
    vma->vm_ops = &ceph_vmops;
    return 0;
}