mm/filemap_xip.c: fix race condition in xip_file_fault()

[linux-2.6.git] / fs / ceph / addr.c

#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))



/*
 * 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 = (void *)page->private;

        BUG_ON(!PageLocked(page));
        BUG_ON(!page->private);
        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(page->private);
        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,
                                  page->index << PAGE_CACHE_SHIFT, &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 = page->index << PAGE_CACHE_SHIFT;

        /* 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 (!req)
                return -ENOMEM;

        /* 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->index << PAGE_CACHE_SHIFT;
        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 = (void *)page->private;
        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, (void *)page->private);
                /* 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((void *)page->private);
                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 = (void *)page->private;
                        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 = (unsigned long long)page->index
                                        << PAGE_CACHE_SHIFT;
                                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 (!req) {
                                        rc = -ENOMEM;
                                        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 = (void *)page->private;
        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->index << PAGE_CACHE_SHIFT;
        loff_t size, len;
        int ret;

        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,
};

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;
        vma->vm_flags |= VM_CAN_NONLINEAR;
        return 0;
}