[safe/jmp/linux-2.6] / fs / xfs / linux-2.6 / xfs_aops.c

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * 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.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dir.h"
#include "xfs_dir2.h"
#include "xfs_trans.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dir_sf.h"
#include "xfs_dir2_sf.h"
#include "xfs_attr_sf.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_alloc.h"
#include "xfs_btree.h"
#include "xfs_error.h"
#include "xfs_rw.h"
#include "xfs_iomap.h"
#include <linux/mpage.h>
#include <linux/writeback.h>

STATIC void xfs_count_page_state(struct page *, int *, int *, int *);
STATIC void xfs_convert_page(struct inode *, struct page *, xfs_iomap_t *,
                struct writeback_control *wbc, void *, int, int);

#if defined(XFS_RW_TRACE)
void
xfs_page_trace(
        int             tag,
        struct inode    *inode,
        struct page     *page,
        int             mask)
{
        xfs_inode_t     *ip;
        bhv_desc_t      *bdp;
        vnode_t         *vp = LINVFS_GET_VP(inode);
        loff_t          isize = i_size_read(inode);
        loff_t          offset = (loff_t)page->index << PAGE_CACHE_SHIFT;
        int             delalloc = -1, unmapped = -1, unwritten = -1;

        if (page_has_buffers(page))
                xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);

        bdp = vn_bhv_lookup(VN_BHV_HEAD(vp), &xfs_vnodeops);
        ip = XFS_BHVTOI(bdp);
        if (!ip->i_rwtrace)
                return;

        ktrace_enter(ip->i_rwtrace,
                (void *)((unsigned long)tag),
                (void *)ip,
                (void *)inode,
                (void *)page,
                (void *)((unsigned long)mask),
                (void *)((unsigned long)((ip->i_d.di_size >> 32) & 0xffffffff)),
                (void *)((unsigned long)(ip->i_d.di_size & 0xffffffff)),
                (void *)((unsigned long)((isize >> 32) & 0xffffffff)),
                (void *)((unsigned long)(isize & 0xffffffff)),
                (void *)((unsigned long)((offset >> 32) & 0xffffffff)),
                (void *)((unsigned long)(offset & 0xffffffff)),
                (void *)((unsigned long)delalloc),
                (void *)((unsigned long)unmapped),
                (void *)((unsigned long)unwritten),
                (void *)NULL,
                (void *)NULL);
}
#else
#define xfs_page_trace(tag, inode, page, mask)
#endif

/*
 * Schedule IO completion handling on a xfsdatad if this was
 * the final hold on this ioend.
 */
STATIC void
xfs_finish_ioend(
        xfs_ioend_t             *ioend)
{
        if (atomic_dec_and_test(&ioend->io_remaining))
                queue_work(xfsdatad_workqueue, &ioend->io_work);
}

STATIC void
xfs_destroy_ioend(
        xfs_ioend_t             *ioend)
{
        vn_iowake(ioend->io_vnode);
        mempool_free(ioend, xfs_ioend_pool);
}

/*
 * Issue transactions to convert a buffer range from unwritten
 * to written extents.
 */
STATIC void
xfs_end_bio_unwritten(
        void                    *data)
{
        xfs_ioend_t             *ioend = data;
        vnode_t                 *vp = ioend->io_vnode;
        xfs_off_t               offset = ioend->io_offset;
        size_t                  size = ioend->io_size;
        struct buffer_head      *bh, *next;
        int                     error;

        if (ioend->io_uptodate)
                VOP_BMAP(vp, offset, size, BMAPI_UNWRITTEN, NULL, NULL, error);

        /* ioend->io_buffer_head is only non-NULL for buffered I/O */
        for (bh = ioend->io_buffer_head; bh; bh = next) {
                next = bh->b_private;

                bh->b_end_io = NULL;
                clear_buffer_unwritten(bh);
                end_buffer_async_write(bh, ioend->io_uptodate);
        }

        xfs_destroy_ioend(ioend);
}

/*
 * Allocate and initialise an IO completion structure.
 * We need to track unwritten extent write completion here initially.
 * We'll need to extend this for updating the ondisk inode size later
 * (vs. incore size).
 */
STATIC xfs_ioend_t *
xfs_alloc_ioend(
        struct inode            *inode)
{
        xfs_ioend_t             *ioend;

        ioend = mempool_alloc(xfs_ioend_pool, GFP_NOFS);

        /*
         * Set the count to 1 initially, which will prevent an I/O
         * completion callback from happening before we have started
         * all the I/O from calling the completion routine too early.
         */
        atomic_set(&ioend->io_remaining, 1);
        ioend->io_uptodate = 1; /* cleared if any I/O fails */
        ioend->io_vnode = LINVFS_GET_VP(inode);
        ioend->io_buffer_head = NULL;
        atomic_inc(&ioend->io_vnode->v_iocount);
        ioend->io_offset = 0;
        ioend->io_size = 0;

        INIT_WORK(&ioend->io_work, xfs_end_bio_unwritten, ioend);

        return ioend;
}

void
linvfs_unwritten_done(
        struct buffer_head      *bh,
        int                     uptodate)
{
        xfs_ioend_t             *ioend = bh->b_private;
        static spinlock_t       unwritten_done_lock = SPIN_LOCK_UNLOCKED;
        unsigned long           flags;

        ASSERT(buffer_unwritten(bh));
        bh->b_end_io = NULL;

        if (!uptodate)
                ioend->io_uptodate = 0;

        /*
         * Deep magic here.  We reuse b_private in the buffer_heads to build
         * a chain for completing the I/O from user context after we've issued
         * a transaction to convert the unwritten extent.
         */
        spin_lock_irqsave(&unwritten_done_lock, flags);
        bh->b_private = ioend->io_buffer_head;
        ioend->io_buffer_head = bh;
        spin_unlock_irqrestore(&unwritten_done_lock, flags);

        xfs_finish_ioend(ioend);
}

STATIC int
xfs_map_blocks(
        struct inode            *inode,
        loff_t                  offset,
        ssize_t                 count,
        xfs_iomap_t             *mapp,
        int                     flags)
{
        vnode_t                 *vp = LINVFS_GET_VP(inode);
        int                     error, nmaps = 1;

        VOP_BMAP(vp, offset, count, flags, mapp, &nmaps, error);
        if (!error && (flags & (BMAPI_WRITE|BMAPI_ALLOCATE)))
                VMODIFY(vp);
        return -error;
}

/*
 * Finds the corresponding mapping in block @map array of the
 * given @offset within a @page.
 */
STATIC xfs_iomap_t *
xfs_offset_to_map(
        struct page             *page,
        xfs_iomap_t             *iomapp,
        unsigned long           offset)
{
        loff_t                  full_offset;    /* offset from start of file */

        ASSERT(offset < PAGE_CACHE_SIZE);

        full_offset = page->index;              /* NB: using 64bit number */
        full_offset <<= PAGE_CACHE_SHIFT;       /* offset from file start */
        full_offset += offset;                  /* offset from page start */

        if (full_offset < iomapp->iomap_offset)
                return NULL;
        if (iomapp->iomap_offset + (iomapp->iomap_bsize -1) >= full_offset)
                return iomapp;
        return NULL;
}

STATIC void
xfs_map_at_offset(
        struct page             *page,
        struct buffer_head      *bh,
        unsigned long           offset,
        int                     block_bits,
        xfs_iomap_t             *iomapp)
{
        xfs_daddr_t             bn;
        loff_t                  delta;
        int                     sector_shift;

        ASSERT(!(iomapp->iomap_flags & IOMAP_HOLE));
        ASSERT(!(iomapp->iomap_flags & IOMAP_DELAY));
        ASSERT(iomapp->iomap_bn != IOMAP_DADDR_NULL);

        delta = page->index;
        delta <<= PAGE_CACHE_SHIFT;
        delta += offset;
        delta -= iomapp->iomap_offset;
        delta >>= block_bits;

        sector_shift = block_bits - BBSHIFT;
        bn = iomapp->iomap_bn >> sector_shift;
        bn += delta;
        BUG_ON(!bn && !(iomapp->iomap_flags & IOMAP_REALTIME));
        ASSERT((bn << sector_shift) >= iomapp->iomap_bn);

        lock_buffer(bh);
        bh->b_blocknr = bn;
        bh->b_bdev = iomapp->iomap_target->pbr_bdev;
        set_buffer_mapped(bh);
        clear_buffer_delay(bh);
}

/*
 * Look for a page at index which is unlocked and contains our
 * unwritten extent flagged buffers at its head.  Returns page
 * locked and with an extra reference count, and length of the
 * unwritten extent component on this page that we can write,
 * in units of filesystem blocks.
 */
STATIC struct page *
xfs_probe_unwritten_page(
        struct address_space    *mapping,
        pgoff_t                 index,
        xfs_iomap_t             *iomapp,
        xfs_ioend_t             *ioend,
        unsigned long           max_offset,
        unsigned long           *fsbs,
        unsigned int            bbits)
{
        struct page             *page;

        page = find_trylock_page(mapping, index);
        if (!page)
                return NULL;
        if (PageWriteback(page))
                goto out;

        if (page->mapping && page_has_buffers(page)) {
                struct buffer_head      *bh, *head;
                unsigned long           p_offset = 0;

                *fsbs = 0;
                bh = head = page_buffers(page);
                do {
                        if (!buffer_unwritten(bh) || !buffer_uptodate(bh))
                                break;
                        if (!xfs_offset_to_map(page, iomapp, p_offset))
                                break;
                        if (p_offset >= max_offset)
                                break;
                        xfs_map_at_offset(page, bh, p_offset, bbits, iomapp);
                        set_buffer_unwritten_io(bh);
                        bh->b_private = ioend;
                        p_offset += bh->b_size;
                        (*fsbs)++;
                } while ((bh = bh->b_this_page) != head);

                if (p_offset)
                        return page;
        }

out:
        unlock_page(page);
        return NULL;
}

/*
 * Look for a page at index which is unlocked and not mapped
 * yet - clustering for mmap write case.
 */
STATIC unsigned int
xfs_probe_unmapped_page(
        struct address_space    *mapping,
        pgoff_t                 index,
        unsigned int            pg_offset)
{
        struct page             *page;
        int                     ret = 0;

        page = find_trylock_page(mapping, index);
        if (!page)
                return 0;
        if (PageWriteback(page))
                goto out;

        if (page->mapping && PageDirty(page)) {
                if (page_has_buffers(page)) {
                        struct buffer_head      *bh, *head;

                        bh = head = page_buffers(page);
                        do {
                                if (buffer_mapped(bh) || !buffer_uptodate(bh))
                                        break;
                                ret += bh->b_size;
                                if (ret >= pg_offset)
                                        break;
                        } while ((bh = bh->b_this_page) != head);
                } else
                        ret = PAGE_CACHE_SIZE;
        }

out:
        unlock_page(page);
        return ret;
}

STATIC unsigned int
xfs_probe_unmapped_cluster(
        struct inode            *inode,
        struct page             *startpage,
        struct buffer_head      *bh,
        struct buffer_head      *head)
{
        pgoff_t                 tindex, tlast, tloff;
        unsigned int            pg_offset, len, total = 0;
        struct address_space    *mapping = inode->i_mapping;

        /* First sum forwards in this page */
        do {
                if (buffer_mapped(bh))
                        break;
                total += bh->b_size;
        } while ((bh = bh->b_this_page) != head);

        /* If we reached the end of the page, sum forwards in
         * following pages.
         */
        if (bh == head) {
                tlast = i_size_read(inode) >> PAGE_CACHE_SHIFT;
                /* Prune this back to avoid pathological behavior */
                tloff = min(tlast, startpage->index + 64);
                for (tindex = startpage->index + 1; tindex < tloff; tindex++) {
                        len = xfs_probe_unmapped_page(mapping, tindex,
                                                        PAGE_CACHE_SIZE);
                        if (!len)
                                return total;
                        total += len;
                }
                if (tindex == tlast &&
                    (pg_offset = i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
                        total += xfs_probe_unmapped_page(mapping,
                                                        tindex, pg_offset);
                }
        }
        return total;
}

/*
 * Probe for a given page (index) in the inode and test if it is delayed
 * and without unwritten buffers.  Returns page locked and with an extra
 * reference count.
 */
STATIC struct page *
xfs_probe_delalloc_page(
        struct inode            *inode,
        pgoff_t                 index)
{
        struct page             *page;

        page = find_trylock_page(inode->i_mapping, index);
        if (!page)
                return NULL;
        if (PageWriteback(page))
                goto out;

        if (page->mapping && page_has_buffers(page)) {
                struct buffer_head      *bh, *head;
                int                     acceptable = 0;

                bh = head = page_buffers(page);
                do {
                        if (buffer_unwritten(bh)) {
                                acceptable = 0;
                                break;
                        } else if (buffer_delay(bh)) {
                                acceptable = 1;
                        }
                } while ((bh = bh->b_this_page) != head);

                if (acceptable)
                        return page;
        }

out:
        unlock_page(page);
        return NULL;
}

STATIC int
xfs_map_unwritten(
        struct inode            *inode,
        struct page             *start_page,
        struct buffer_head      *head,
        struct buffer_head      *curr,
        unsigned long           p_offset,
        int                     block_bits,
        xfs_iomap_t             *iomapp,
        struct writeback_control *wbc,
        int                     startio,
        int                     all_bh)
{
        struct buffer_head      *bh = curr;
        xfs_iomap_t             *tmp;
        xfs_ioend_t             *ioend;
        loff_t                  offset;
        unsigned long           nblocks = 0;

        offset = start_page->index;
        offset <<= PAGE_CACHE_SHIFT;
        offset += p_offset;

        ioend = xfs_alloc_ioend(inode);

        /* First map forwards in the page consecutive buffers
         * covering this unwritten extent
         */
        do {
                if (!buffer_unwritten(bh))
                        break;
                tmp = xfs_offset_to_map(start_page, iomapp, p_offset);
                if (!tmp)
                        break;
                xfs_map_at_offset(start_page, bh, p_offset, block_bits, iomapp);
                set_buffer_unwritten_io(bh);
                bh->b_private = ioend;
                p_offset += bh->b_size;
                nblocks++;
        } while ((bh = bh->b_this_page) != head);

        atomic_add(nblocks, &ioend->io_remaining);

        /* If we reached the end of the page, map forwards in any
         * following pages which are also covered by this extent.
         */
        if (bh == head) {
                struct address_space    *mapping = inode->i_mapping;
                pgoff_t                 tindex, tloff, tlast;
                unsigned long           bs;
                unsigned int            pg_offset, bbits = inode->i_blkbits;
                struct page             *page;

                tlast = i_size_read(inode) >> PAGE_CACHE_SHIFT;
                tloff = (iomapp->iomap_offset + iomapp->iomap_bsize) >> PAGE_CACHE_SHIFT;
                tloff = min(tlast, tloff);
                for (tindex = start_page->index + 1; tindex < tloff; tindex++) {
                        page = xfs_probe_unwritten_page(mapping,
                                                tindex, iomapp, ioend,
                                                PAGE_CACHE_SIZE, &bs, bbits);
                        if (!page)
                                break;
                        nblocks += bs;
                        atomic_add(bs, &ioend->io_remaining);
                        xfs_convert_page(inode, page, iomapp, wbc, ioend,
                                                        startio, all_bh);
                        /* stop if converting the next page might add
                         * enough blocks that the corresponding byte
                         * count won't fit in our ulong page buf length */
                        if (nblocks >= ((ULONG_MAX - PAGE_SIZE) >> block_bits))
                                goto enough;
                }

                if (tindex == tlast &&
                    (pg_offset = (i_size_read(inode) & (PAGE_CACHE_SIZE - 1)))) {
                        page = xfs_probe_unwritten_page(mapping,
                                                        tindex, iomapp, ioend,
                                                        pg_offset, &bs, bbits);
                        if (page) {
                                nblocks += bs;
                                atomic_add(bs, &ioend->io_remaining);
                                xfs_convert_page(inode, page, iomapp, wbc, ioend,
                                                        startio, all_bh);
                                if (nblocks >= ((ULONG_MAX - PAGE_SIZE) >> block_bits))
                                        goto enough;
                        }
                }
        }

enough:
        ioend->io_size = (xfs_off_t)nblocks << block_bits;
        ioend->io_offset = offset;
        xfs_finish_ioend(ioend);
        return 0;
}

STATIC void
xfs_submit_page(
        struct page             *page,
        struct writeback_control *wbc,
        struct buffer_head      *bh_arr[],
        int                     bh_count,
        int                     probed_page,
        int                     clear_dirty)
{
        struct buffer_head      *bh;
        int                     i;

        BUG_ON(PageWriteback(page));
        if (bh_count)
                set_page_writeback(page);
        if (clear_dirty)
                clear_page_dirty(page);
        unlock_page(page);

        if (bh_count) {
                for (i = 0; i < bh_count; i++) {
                        bh = bh_arr[i];
                        mark_buffer_async_write(bh);
                        if (buffer_unwritten(bh))
                                set_buffer_unwritten_io(bh);
                        set_buffer_uptodate(bh);
                        clear_buffer_dirty(bh);
                }

                for (i = 0; i < bh_count; i++)
                        submit_bh(WRITE, bh_arr[i]);

                if (probed_page && clear_dirty)
                        wbc->nr_to_write--;     /* Wrote an "extra" page */
        }
}

/*
 * Allocate & map buffers for page given the extent map. Write it out.
 * except for the original page of a writepage, this is called on
 * delalloc/unwritten pages only, for the original page it is possible
 * that the page has no mapping at all.
 */
STATIC void
xfs_convert_page(
        struct inode            *inode,
        struct page             *page,
        xfs_iomap_t             *iomapp,
        struct writeback_control *wbc,
        void                    *private,
        int                     startio,
        int                     all_bh)
{
        struct buffer_head      *bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
        xfs_iomap_t             *mp = iomapp, *tmp;
        unsigned long           offset, end_offset;
        int                     index = 0;
        int                     bbits = inode->i_blkbits;
        int                     len, page_dirty;

        end_offset = (i_size_read(inode) & (PAGE_CACHE_SIZE - 1));

        /*
         * page_dirty is initially a count of buffers on the page before
         * EOF and is decrememted as we move each into a cleanable state.
         */
        len = 1 << inode->i_blkbits;
        end_offset = max(end_offset, PAGE_CACHE_SIZE);
        end_offset = roundup(end_offset, len);
        page_dirty = end_offset / len;

        offset = 0;
        bh = head = page_buffers(page);
        do {
                if (offset >= end_offset)
                        break;
                if (!(PageUptodate(page) || buffer_uptodate(bh)))
                        continue;
                if (buffer_mapped(bh) && all_bh &&
                    !(buffer_unwritten(bh) || buffer_delay(bh))) {
                        if (startio) {
                                lock_buffer(bh);
                                bh_arr[index++] = bh;
                                page_dirty--;
                        }
                        continue;
                }
                tmp = xfs_offset_to_map(page, mp, offset);
                if (!tmp)
                        continue;
                ASSERT(!(tmp->iomap_flags & IOMAP_HOLE));
                ASSERT(!(tmp->iomap_flags & IOMAP_DELAY));

                /* If this is a new unwritten extent buffer (i.e. one
                 * that we haven't passed in private data for, we must
                 * now map this buffer too.
                 */
                if (buffer_unwritten(bh) && !bh->b_end_io) {
                        ASSERT(tmp->iomap_flags & IOMAP_UNWRITTEN);
                        xfs_map_unwritten(inode, page, head, bh, offset,
                                        bbits, tmp, wbc, startio, all_bh);
                } else if (! (buffer_unwritten(bh) && buffer_locked(bh))) {
                        xfs_map_at_offset(page, bh, offset, bbits, tmp);
                        if (buffer_unwritten(bh)) {
                                set_buffer_unwritten_io(bh);
                                bh->b_private = private;
                                ASSERT(private);
                        }
                }
                if (startio) {
                        bh_arr[index++] = bh;
                } else {
                        set_buffer_dirty(bh);
                        unlock_buffer(bh);
                        mark_buffer_dirty(bh);
                }
                page_dirty--;
        } while (offset += len, (bh = bh->b_this_page) != head);

        if (startio && index) {
                xfs_submit_page(page, wbc, bh_arr, index, 1, !page_dirty);
        } else {
                unlock_page(page);
        }
}

/*
 * Convert & write out a cluster of pages in the same extent as defined
 * by mp and following the start page.
 */
STATIC void
xfs_cluster_write(
        struct inode            *inode,
        pgoff_t                 tindex,
        xfs_iomap_t             *iomapp,
        struct writeback_control *wbc,
        int                     startio,
        int                     all_bh,
        pgoff_t                 tlast)
{
        struct page             *page;

        for (; tindex <= tlast; tindex++) {
                page = xfs_probe_delalloc_page(inode, tindex);
                if (!page)
                        break;
                xfs_convert_page(inode, page, iomapp, wbc, NULL,
                                startio, all_bh);
        }
}

/*
 * Calling this without startio set means we are being asked to make a dirty
 * page ready for freeing it's buffers.  When called with startio set then
 * we are coming from writepage.
 *
 * When called with startio set it is important that we write the WHOLE
 * page if possible.
 * The bh->b_state's cannot know if any of the blocks or which block for
 * that matter are dirty due to mmap writes, and therefore bh uptodate is
 * only vaild if the page itself isn't completely uptodate.  Some layers
 * may clear the page dirty flag prior to calling write page, under the
 * assumption the entire page will be written out; by not writing out the
 * whole page the page can be reused before all valid dirty data is
 * written out.  Note: in the case of a page that has been dirty'd by
 * mapwrite and but partially setup by block_prepare_write the
 * bh->b_states's will not agree and only ones setup by BPW/BCW will have
 * valid state, thus the whole page must be written out thing.
 */

STATIC int
xfs_page_state_convert(
        struct inode    *inode,
        struct page     *page,
        struct writeback_control *wbc,
        int             startio,
        int             unmapped) /* also implies page uptodate */
{
        struct buffer_head      *bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
        xfs_iomap_t             *iomp, iomap;
        loff_t                  offset;
        unsigned long           p_offset = 0;
        __uint64_t              end_offset;
        pgoff_t                 end_index, last_index, tlast;
        int                     len, err, i, cnt = 0, uptodate = 1;
        int                     flags;
        int                     page_dirty;

        /* wait for other IO threads? */
        flags = (startio && wbc->sync_mode != WB_SYNC_NONE) ? 0 : BMAPI_TRYLOCK;

        /* Is this page beyond the end of the file? */
        offset = i_size_read(inode);
        end_index = offset >> PAGE_CACHE_SHIFT;
        last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
        if (page->index >= end_index) {
                if ((page->index >= end_index + 1) ||
                    !(i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
                        err = -EIO;
                        goto error;
                }
        }

        end_offset = min_t(unsigned long long,
                        (loff_t)(page->index + 1) << PAGE_CACHE_SHIFT, offset);
        offset = (loff_t)page->index << PAGE_CACHE_SHIFT;

        /*
         * page_dirty is initially a count of buffers on the page before
         * EOF and is decrememted as we move each into a cleanable state.
         */
        len = 1 << inode->i_blkbits;
        p_offset = max(p_offset, PAGE_CACHE_SIZE);
        p_offset = roundup(p_offset, len);
        page_dirty = p_offset / len;

        iomp = NULL;
        p_offset = 0;
        bh = head = page_buffers(page);

        do {
                if (offset >= end_offset)
                        break;
                if (!buffer_uptodate(bh))
                        uptodate = 0;
                if (!(PageUptodate(page) || buffer_uptodate(bh)) && !startio)
                        continue;

                if (iomp) {
                        iomp = xfs_offset_to_map(page, &iomap, p_offset);
                }

                /*
                 * First case, map an unwritten extent and prepare for
                 * extent state conversion transaction on completion.
                 */
                if (buffer_unwritten(bh)) {
                        if (!startio)
                                continue;
                        if (!iomp) {
                                err = xfs_map_blocks(inode, offset, len, &iomap,
                                                BMAPI_WRITE|BMAPI_IGNSTATE);
                                if (err) {
                                        goto error;
                                }
                                iomp = xfs_offset_to_map(page, &iomap,
                                                                p_offset);
                        }
                        if (iomp) {
                                if (!bh->b_end_io) {
                                        err = xfs_map_unwritten(inode, page,
                                                        head, bh, p_offset,
                                                        inode->i_blkbits, iomp,
                                                        wbc, startio, unmapped);
                                        if (err) {
                                                goto error;
                                        }
                                } else {
                                        set_bit(BH_Lock, &bh->b_state);
                                }
                                BUG_ON(!buffer_locked(bh));
                                bh_arr[cnt++] = bh;
                                page_dirty--;
                        }
                /*
                 * Second case, allocate space for a delalloc buffer.
                 * We can return EAGAIN here in the release page case.
                 */
                } else if (buffer_delay(bh)) {
                        if (!iomp) {
                                err = xfs_map_blocks(inode, offset, len, &iomap,
                                                BMAPI_ALLOCATE | flags);
                                if (err) {
                                        goto error;
                                }
                                iomp = xfs_offset_to_map(page, &iomap,
                                                                p_offset);
                        }
                        if (iomp) {
                                xfs_map_at_offset(page, bh, p_offset,
                                                inode->i_blkbits, iomp);
                                if (startio) {
                                        bh_arr[cnt++] = bh;
                                } else {
                                        set_buffer_dirty(bh);
                                        unlock_buffer(bh);
                                        mark_buffer_dirty(bh);
                                }
                                page_dirty--;
                        }
                } else if ((buffer_uptodate(bh) || PageUptodate(page)) &&
                           (unmapped || startio)) {

                        if (!buffer_mapped(bh)) {
                                int     size;

                                /*
                                 * Getting here implies an unmapped buffer
                                 * was found, and we are in a path where we
                                 * need to write the whole page out.
                                 */
                                if (!iomp) {
                                        size = xfs_probe_unmapped_cluster(
                                                        inode, page, bh, head);
                                        err = xfs_map_blocks(inode, offset,
                                                        size, &iomap,
                                                        BMAPI_WRITE|BMAPI_MMAP);
                                        if (err) {
                                                goto error;
                                        }
                                        iomp = xfs_offset_to_map(page, &iomap,
                                                                     p_offset);
                                }
                                if (iomp) {
                                        xfs_map_at_offset(page,
                                                        bh, p_offset,
                                                        inode->i_blkbits, iomp);
                                        if (startio) {
                                                bh_arr[cnt++] = bh;
                                        } else {
                                                set_buffer_dirty(bh);
                                                unlock_buffer(bh);
                                                mark_buffer_dirty(bh);
                                        }
                                        page_dirty--;
                                }
                        } else if (startio) {
                                if (buffer_uptodate(bh) &&
                                    !test_and_set_bit(BH_Lock, &bh->b_state)) {
                                        bh_arr[cnt++] = bh;
                                        page_dirty--;
                                }
                        }
                }
        } while (offset += len, p_offset += len,
                ((bh = bh->b_this_page) != head));

        if (uptodate && bh == head)
                SetPageUptodate(page);

        if (startio) {
                xfs_submit_page(page, wbc, bh_arr, cnt, 0, !page_dirty);
        }

        if (iomp) {
                offset = (iomp->iomap_offset + iomp->iomap_bsize - 1) >>
                                        PAGE_CACHE_SHIFT;
                tlast = min_t(pgoff_t, offset, last_index);
                xfs_cluster_write(inode, page->index + 1, iomp, wbc,
                                        startio, unmapped, tlast);
        }

        return page_dirty;

error:
        for (i = 0; i < cnt; i++) {
                unlock_buffer(bh_arr[i]);
        }

        /*
         * If it's delalloc and we have nowhere to put it,
         * throw it away, unless the lower layers told
         * us to try again.
         */
        if (err != -EAGAIN) {
                if (!unmapped) {
                        block_invalidatepage(page, 0);
                }
                ClearPageUptodate(page);
        }
        return err;
}

STATIC int
__linvfs_get_block(
        struct inode            *inode,
        sector_t                iblock,
        unsigned long           blocks,
        struct buffer_head      *bh_result,
        int                     create,
        int                     direct,
        bmapi_flags_t           flags)
{
        vnode_t                 *vp = LINVFS_GET_VP(inode);
        xfs_iomap_t             iomap;
        xfs_off_t               offset;
        ssize_t                 size;
        int                     retpbbm = 1;
        int                     error;

        if (blocks) {
                offset = blocks << inode->i_blkbits;    /* 64 bit goodness */
                size = (ssize_t) min_t(xfs_off_t, offset, LONG_MAX);
        } else {
                size = 1 << inode->i_blkbits;
        }
        offset = (xfs_off_t)iblock << inode->i_blkbits;

        VOP_BMAP(vp, offset, size,
                create ? flags : BMAPI_READ, &iomap, &retpbbm, error);
        if (error)
                return -error;

        if (retpbbm == 0)
                return 0;

        if (iomap.iomap_bn != IOMAP_DADDR_NULL) {
                xfs_daddr_t     bn;
                xfs_off_t       delta;

                /* For unwritten extents do not report a disk address on
                 * the read case (treat as if we're reading into a hole).
                 */
                if (create || !(iomap.iomap_flags & IOMAP_UNWRITTEN)) {
                        delta = offset - iomap.iomap_offset;
                        delta >>= inode->i_blkbits;

                        bn = iomap.iomap_bn >> (inode->i_blkbits - BBSHIFT);
                        bn += delta;
                        BUG_ON(!bn && !(iomap.iomap_flags & IOMAP_REALTIME));
                        bh_result->b_blocknr = bn;
                        set_buffer_mapped(bh_result);
                }
                if (create && (iomap.iomap_flags & IOMAP_UNWRITTEN)) {
                        if (direct)
                                bh_result->b_private = inode;
                        set_buffer_unwritten(bh_result);
                        set_buffer_delay(bh_result);
                }
        }

        /* If this is a realtime file, data might be on a new device */
        bh_result->b_bdev = iomap.iomap_target->pbr_bdev;

        /* If we previously allocated a block out beyond eof and
         * we are now coming back to use it then we will need to
         * flag it as new even if it has a disk address.
         */
        if (create &&
            ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||
             (offset >= i_size_read(inode)) || (iomap.iomap_flags & IOMAP_NEW)))
                set_buffer_new(bh_result);

        if (iomap.iomap_flags & IOMAP_DELAY) {
                BUG_ON(direct);
                if (create) {
                        set_buffer_uptodate(bh_result);
                        set_buffer_mapped(bh_result);
                        set_buffer_delay(bh_result);
                }
        }

        if (blocks) {
                ASSERT(iomap.iomap_bsize - iomap.iomap_delta > 0);
                offset = min_t(xfs_off_t,
                                iomap.iomap_bsize - iomap.iomap_delta,
                                blocks << inode->i_blkbits);
                bh_result->b_size = (u32) min_t(xfs_off_t, UINT_MAX, offset);
        }

        return 0;
}

int
linvfs_get_block(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __linvfs_get_block(inode, iblock, 0, bh_result,
                                        create, 0, BMAPI_WRITE);
}

STATIC int
linvfs_get_blocks_direct(
        struct inode            *inode,
        sector_t                iblock,
        unsigned long           max_blocks,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __linvfs_get_block(inode, iblock, max_blocks, bh_result,
                                        create, 1, BMAPI_WRITE|BMAPI_DIRECT);
}

STATIC void
linvfs_end_io_direct(
        struct kiocb    *iocb,
        loff_t          offset,
        ssize_t         size,
        void            *private)
{
        xfs_ioend_t     *ioend = iocb->private;

        /*
         * Non-NULL private data means we need to issue a transaction to
         * convert a range from unwritten to written extents.  This needs
         * to happen from process contect but aio+dio I/O completion
         * happens from irq context so we need to defer it to a workqueue.
         * This is not nessecary for synchronous direct I/O, but we do
         * it anyway to keep the code uniform and simpler.
         *
         * The core direct I/O code might be changed to always call the
         * completion handler in the future, in which case all this can
         * go away.
         */
        if (private && size > 0) {
                ioend->io_offset = offset;
                ioend->io_size = size;
                xfs_finish_ioend(ioend);
        } else {
                ASSERT(size >= 0);
                xfs_destroy_ioend(ioend);
        }

        /*
         * blockdev_direct_IO can return an error even afer the I/O
         * completion handler was called.  Thus we need to protect
         * against double-freeing.
         */
        iocb->private = NULL;
}

STATIC ssize_t
linvfs_direct_IO(
        int                     rw,
        struct kiocb            *iocb,
        const struct iovec      *iov,
        loff_t                  offset,
        unsigned long           nr_segs)
{
        struct file     *file = iocb->ki_filp;
        struct inode    *inode = file->f_mapping->host;
        vnode_t         *vp = LINVFS_GET_VP(inode);
        xfs_iomap_t     iomap;
        int             maps = 1;
        int             error;
        ssize_t         ret;

        VOP_BMAP(vp, offset, 0, BMAPI_DEVICE, &iomap, &maps, error);
        if (error)
                return -error;

        iocb->private = xfs_alloc_ioend(inode);

        ret = blockdev_direct_IO_own_locking(rw, iocb, inode,
                iomap.iomap_target->pbr_bdev,
                iov, offset, nr_segs,
                linvfs_get_blocks_direct,
                linvfs_end_io_direct);

        if (unlikely(ret <= 0 && iocb->private))
                xfs_destroy_ioend(iocb->private);
        return ret;
}


STATIC sector_t
linvfs_bmap(
        struct address_space    *mapping,
        sector_t                block)
{
        struct inode            *inode = (struct inode *)mapping->host;
        vnode_t                 *vp = LINVFS_GET_VP(inode);
        int                     error;

        vn_trace_entry(vp, "linvfs_bmap", (inst_t *)__return_address);

        VOP_RWLOCK(vp, VRWLOCK_READ);
        VOP_FLUSH_PAGES(vp, (xfs_off_t)0, -1, 0, FI_REMAPF, error);
        VOP_RWUNLOCK(vp, VRWLOCK_READ);
        return generic_block_bmap(mapping, block, linvfs_get_block);
}

STATIC int
linvfs_readpage(
        struct file             *unused,
        struct page             *page)
{
        return mpage_readpage(page, linvfs_get_block);
}

STATIC int
linvfs_readpages(
        struct file             *unused,
        struct address_space    *mapping,
        struct list_head        *pages,
        unsigned                nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, linvfs_get_block);
}

STATIC void
xfs_count_page_state(
        struct page             *page,
        int                     *delalloc,
        int                     *unmapped,
        int                     *unwritten)
{
        struct buffer_head      *bh, *head;

        *delalloc = *unmapped = *unwritten = 0;

        bh = head = page_buffers(page);
        do {
                if (buffer_uptodate(bh) && !buffer_mapped(bh))
                        (*unmapped) = 1;
                else if (buffer_unwritten(bh) && !buffer_delay(bh))
                        clear_buffer_unwritten(bh);
                else if (buffer_unwritten(bh))
                        (*unwritten) = 1;
                else if (buffer_delay(bh))
                        (*delalloc) = 1;
        } while ((bh = bh->b_this_page) != head);
}


/*
 * writepage: Called from one of two places:
 *
 * 1. we are flushing a delalloc buffer head.
 *
 * 2. we are writing out a dirty page. Typically the page dirty
 *    state is cleared before we get here. In this case is it
 *    conceivable we have no buffer heads.
 *
 * For delalloc space on the page we need to allocate space and
 * flush it. For unmapped buffer heads on the page we should
 * allocate space if the page is uptodate. For any other dirty
 * buffer heads on the page we should flush them.
 *
 * If we detect that a transaction would be required to flush
 * the page, we have to check the process flags first, if we
 * are already in a transaction or disk I/O during allocations
 * is off, we need to fail the writepage and redirty the page.
 */

STATIC int
linvfs_writepage(
        struct page             *page,
        struct writeback_control *wbc)
{
        int                     error;
        int                     need_trans;
        int                     delalloc, unmapped, unwritten;
        struct inode            *inode = page->mapping->host;

        xfs_page_trace(XFS_WRITEPAGE_ENTER, inode, page, 0);

        /*
         * We need a transaction if:
         *  1. There are delalloc buffers on the page
         *  2. The page is uptodate and we have unmapped buffers
         *  3. The page is uptodate and we have no buffers
         *  4. There are unwritten buffers on the page
         */

        if (!page_has_buffers(page)) {
                unmapped = 1;
                need_trans = 1;
        } else {
                xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
                if (!PageUptodate(page))
                        unmapped = 0;
                need_trans = delalloc + unmapped + unwritten;
        }

        /*
         * If we need a transaction and the process flags say
         * we are already in a transaction, or no IO is allowed
         * then mark the page dirty again and leave the page
         * as is.
         */
        if (PFLAGS_TEST_FSTRANS() && need_trans)
                goto out_fail;

        /*
         * Delay hooking up buffer heads until we have
         * made our go/no-go decision.
         */
        if (!page_has_buffers(page))
                create_empty_buffers(page, 1 << inode->i_blkbits, 0);

        /*
         * Convert delayed allocate, unwritten or unmapped space
         * to real space and flush out to disk.
         */
        error = xfs_page_state_convert(inode, page, wbc, 1, unmapped);
        if (error == -EAGAIN)
                goto out_fail;
        if (unlikely(error < 0))
                goto out_unlock;

        return 0;

out_fail:
        redirty_page_for_writepage(wbc, page);
        unlock_page(page);
        return 0;
out_unlock:
        unlock_page(page);
        return error;
}

STATIC int
linvfs_invalidate_page(
        struct page             *page,
        unsigned long           offset)
{
        xfs_page_trace(XFS_INVALIDPAGE_ENTER,
                        page->mapping->host, page, offset);
        return block_invalidatepage(page, offset);
}

/*
 * Called to move a page into cleanable state - and from there
 * to be released. Possibly the page is already clean. We always
 * have buffer heads in this call.
 *
 * Returns 0 if the page is ok to release, 1 otherwise.
 *
 * Possible scenarios are:
 *
 * 1. We are being called to release a page which has been written
 *    to via regular I/O. buffer heads will be dirty and possibly
 *    delalloc. If no delalloc buffer heads in this case then we
 *    can just return zero.
 *
 * 2. We are called to release a page which has been written via
 *    mmap, all we need to do is ensure there is no delalloc
 *    state in the buffer heads, if not we can let the caller
 *    free them and we should come back later via writepage.
 */
STATIC int
linvfs_release_page(
        struct page             *page,
        gfp_t                   gfp_mask)
{
        struct inode            *inode = page->mapping->host;
        int                     dirty, delalloc, unmapped, unwritten;
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = 1,
        };

        xfs_page_trace(XFS_RELEASEPAGE_ENTER, inode, page, gfp_mask);

        xfs_count_page_state(page, &delalloc, &unmapped, &unwritten);
        if (!delalloc && !unwritten)
                goto free_buffers;

        if (!(gfp_mask & __GFP_FS))
                return 0;

        /* If we are already inside a transaction or the thread cannot
         * do I/O, we cannot release this page.
         */
        if (PFLAGS_TEST_FSTRANS())
                return 0;

        /*
         * Convert delalloc space to real space, do not flush the
         * data out to disk, that will be done by the caller.
         * Never need to allocate space here - we will always
         * come back to writepage in that case.
         */
        dirty = xfs_page_state_convert(inode, page, &wbc, 0, 0);
        if (dirty == 0 && !unwritten)
                goto free_buffers;
        return 0;

free_buffers:
        return try_to_free_buffers(page);
}

STATIC int
linvfs_prepare_write(
        struct file             *file,
        struct page             *page,
        unsigned int            from,
        unsigned int            to)
{
        return block_prepare_write(page, from, to, linvfs_get_block);
}

struct address_space_operations linvfs_aops = {
        .readpage               = linvfs_readpage,
        .readpages              = linvfs_readpages,
        .writepage              = linvfs_writepage,
        .sync_page              = block_sync_page,
        .releasepage            = linvfs_release_page,
        .invalidatepage         = linvfs_invalidate_page,
        .prepare_write          = linvfs_prepare_write,
        .commit_write           = generic_commit_write,
        .bmap                   = linvfs_bmap,
        .direct_IO              = linvfs_direct_IO,
};