Btrfs: patch queue: page_mkwrite

Signed-off-by: Chris Mason <chris.mason@oracle.com>

5 files changed, 328 insertions, 159 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4bd648d68e88..1e83ad720b10 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1142,6 +1142,8 @@ int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, struct btrfs_path *path,
                         u64 isize);
 /* inode.c */
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+int btrfs_readpage(struct file *file, struct page *page);
 void btrfs_delete_inode(struct inode *inode);
 void btrfs_read_locked_inode(struct inode *inode);
 int btrfs_write_inode(struct inode *inode, int wait);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b0ebba6f2e46..602b63dc76c3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -155,9 +155,9 @@ int btrfs_csum_data(struct btrfs_root * root, char *data, size_t len,
         desc.tfm = tfm;
         desc.flags = 0;
         sg_init_one(&sg, data, len);
-        spin_lock(&root->fs_info->hash_lock);
+        spin_lock_irq(&root->fs_info->hash_lock);
         ret = crypto_hash_digest(&desc, &sg, 1, result);
-        spin_unlock(&root->fs_info->hash_lock);
+        spin_unlock_irq(&root->fs_info->hash_lock);
         if (ret) {
                 printk("digest failed\n");
         }
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 3c140cc1dd05..1068993ab1c9 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -228,6 +228,7 @@ found:
                            path->nodes[0]->b_data,
                            root->fs_info->sb->s_blocksize);
         ret = btrfs_csum_data(root, data, len, &item->csum);
+// printk("file %lu offset %llu csum %X\n", objectid, (unsigned long long)offset, *(int *)(&item->csum));
         btrfs_mark_buffer_dirty(path->nodes[0]);
 fail:
         btrfs_release_path(root, path);
@@ -298,4 +299,3 @@ fail:
         mutex_unlock(&root->fs_info->fs_mutex);
         return ret;
 }
-
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 83836fb3d4e9..de8d47b44e12 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -103,10 +103,6 @@ static int dirty_and_release_pages(struct btrfs_trans_handle *trans,
                 this_write = min((size_t)PAGE_CACHE_SIZE - offset, write_bytes);
                 /* FIXME, one block at a time */
 
-                mutex_lock(&root->fs_info->fs_mutex);
-                trans = btrfs_start_transaction(root, 1);
-                btrfs_set_trans_block_group(trans, inode);
-
                 bh = page_buffers(pages[i]);
 
                 if (buffer_mapped(bh) && bh->b_blocknr == 0) {
@@ -115,6 +111,10 @@ static int dirty_and_release_pages(struct btrfs_trans_handle *trans,
                         char *ptr, *kaddr;
                         u32 datasize;
 
+                        mutex_lock(&root->fs_info->fs_mutex);
+                        trans = btrfs_start_transaction(root, 1);
+                        btrfs_set_trans_block_group(trans, inode);
+
                         /* create an inline extent, and copy the data in */
                         path = btrfs_alloc_path();
                         BUG_ON(!path);
@@ -135,24 +135,19 @@ static int dirty_and_release_pages(struct btrfs_trans_handle *trans,
                         btrfs_set_file_extent_type(ei,
                                                    BTRFS_FILE_EXTENT_INLINE);
                         ptr = btrfs_file_extent_inline_start(ei);
+
                         kaddr = kmap_atomic(bh->b_page, KM_USER0);
                         btrfs_memcpy(root, path->nodes[0]->b_data,
                                      ptr, kaddr + bh_offset(bh),
                                      offset + write_bytes);
                         kunmap_atomic(kaddr, KM_USER0);
+
                         mark_buffer_dirty(path->nodes[0]);
                         btrfs_free_path(path);
-                } else if (buffer_mapped(bh)) {
-                        /* csum the file data */
-                        btrfs_csum_file_block(trans, root, inode->i_ino,
-                                      pages[i]->index << PAGE_CACHE_SHIFT,
-                                      kmap(pages[i]), PAGE_CACHE_SIZE);
-                        kunmap(pages[i]);
+                        ret = btrfs_end_transaction(trans, root);
+                        BUG_ON(ret);
+                        mutex_unlock(&root->fs_info->fs_mutex);
                 }
-                SetPageChecked(pages[i]);
-                ret = btrfs_end_transaction(trans, root);
-                BUG_ON(ret);
-                mutex_unlock(&root->fs_info->fs_mutex);
 
                 ret = btrfs_commit_write(file, pages[i], offset,
                                          offset + this_write);
@@ -503,7 +498,7 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
         if ((pos & (PAGE_CACHE_SIZE - 1))) {
                 pinned[0] = grab_cache_page(inode->i_mapping, first_index);
                 if (!PageUptodate(pinned[0])) {
-                        ret = mpage_readpage(pinned[0], btrfs_get_block);
+                        ret = btrfs_readpage(NULL, pinned[0]);
                         BUG_ON(ret);
                         wait_on_page_locked(pinned[0]);
                 } else {
@@ -513,7 +508,7 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
         if ((pos + count) & (PAGE_CACHE_SIZE - 1)) {
                 pinned[1] = grab_cache_page(inode->i_mapping, last_index);
                 if (!PageUptodate(pinned[1])) {
-                        ret = mpage_readpage(pinned[1], btrfs_get_block);
+                        ret = btrfs_readpage(NULL, pinned[1]);
                         BUG_ON(ret);
                         wait_on_page_locked(pinned[1]);
                 } else {
@@ -633,138 +628,6 @@ out:
         return num_written ? num_written : err;
 }
 
-/*
- * FIXME, do this by stuffing the csum we want in the info hanging off
- * page->private.  For now, verify file csums on read
- */
-static int btrfs_read_actor(read_descriptor_t *desc, struct page *page,
-                        unsigned long offset, unsigned long size)
-{
-        char *kaddr;
-        unsigned long left, count = desc->count;
-        struct inode *inode = page->mapping->host;
-
-        if (size > count)
-                size = count;
-
-        if (!PageChecked(page)) {
-                /* FIXME, do it per block */
-                struct btrfs_root *root = BTRFS_I(inode)->root;
-                int ret;
-                struct buffer_head *bh;
-
-                if (page_has_buffers(page)) {
-                        bh = page_buffers(page);
-                        if (!buffer_mapped(bh)) {
-                                SetPageChecked(page);
-                                goto checked;
-                        }
-                }
-
-                ret = btrfs_csum_verify_file_block(root,
-                                  page->mapping->host->i_ino,
-                                  page->index << PAGE_CACHE_SHIFT,
-                                  kmap(page), PAGE_CACHE_SIZE);
-                if (ret) {
-                        if (ret != -ENOENT) {
-                                printk("failed to verify ino %lu page %lu ret %d\n",
-                                       page->mapping->host->i_ino,
-                                       page->index, ret);
-                                memset(page_address(page), 1, PAGE_CACHE_SIZE);
-                                flush_dcache_page(page);
-                        }
-                }
-                SetPageChecked(page);
-                kunmap(page);
-        }
-checked:
-        /*
-         * Faults on the destination of a read are common, so do it before
-         * taking the kmap.
-         */
-        if (!fault_in_pages_writeable(desc->arg.buf, size)) {
-                kaddr = kmap_atomic(page, KM_USER0);
-                left = __copy_to_user_inatomic(desc->arg.buf,
-                                                kaddr + offset, size);
-                kunmap_atomic(kaddr, KM_USER0);
-                if (left == 0)
-                        goto success;
-        }
-
-        /* Do it the slow way */
-        kaddr = kmap(page);
-        left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
-        kunmap(page);
-
-        if (left) {
-                size -= left;
-                desc->error = -EFAULT;
-        }
-success:
-        desc->count = count - size;
-        desc->written += size;
-        desc->arg.buf += size;
-        return size;
-}
-
-/**
- * btrfs_file_aio_read - filesystem read routine, with a mod to csum verify
- * @iocb:       kernel I/O control block
- * @iov:        io vector request
- * @nr_segs:    number of segments in the iovec
- * @pos:        current file position
- */
-static ssize_t btrfs_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
-                                   unsigned long nr_segs, loff_t pos)
-{
-        struct file *filp = iocb->ki_filp;
-        ssize_t retval;
-        unsigned long seg;
-        size_t count;
-        loff_t *ppos = &iocb->ki_pos;
-
-        count = 0;
-        for (seg = 0; seg < nr_segs; seg++) {
-                const struct iovec *iv = &iov[seg];
-
-                /*
-                 * If any segment has a negative length, or the cumulative
-                 * length ever wraps negative then return -EINVAL.
-                 */
-                count += iv->iov_len;
-                if (unlikely((ssize_t)(count|iv->iov_len) < 0))
-                        return -EINVAL;
-                if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
-                        continue;
-                if (seg == 0)
-                        return -EFAULT;
-                nr_segs = seg;
-                count -= iv->iov_len;   /* This segment is no good */
-                break;
-        }
-        retval = 0;
-        if (count) {
-                for (seg = 0; seg < nr_segs; seg++) {
-                        read_descriptor_t desc;
-
-                        desc.written = 0;
-                        desc.arg.buf = iov[seg].iov_base;
-                        desc.count = iov[seg].iov_len;
-                        if (desc.count == 0)
-                                continue;
-                        desc.error = 0;
-                        do_generic_file_read(filp, ppos, &desc,
-                                             btrfs_read_actor);
-                        retval += desc.written;
-                        if (desc.error) {
-                                retval = retval ?: desc.error;
-                                break;
-                        }
-                }
-        }
-        return retval;
-}
-
 static int btrfs_sync_file(struct file *file,
                            struct dentry *dentry, int datasync)
 {
@@ -789,12 +652,25 @@ out:
         return ret > 0 ? EIO : ret;
 }
 
+static struct vm_operations_struct btrfs_file_vm_ops = {
+        .nopage         = filemap_nopage,
+        .populate       = filemap_populate,
+        .page_mkwrite   = btrfs_page_mkwrite,
+};
+
+static int btrfs_file_mmap(struct file  *filp, struct vm_area_struct *vma)
+{
+        vma->vm_ops = &btrfs_file_vm_ops;
+        file_accessed(filp);
+        return 0;
+}
+
 struct file_operations btrfs_file_operations = {
         .llseek         = generic_file_llseek,
         .read           = do_sync_read,
-        .aio_read       = btrfs_file_aio_read,
+        .aio_read       = generic_file_aio_read,
         .write          = btrfs_file_write,
-        .mmap           = generic_file_mmap,
+        .mmap           = btrfs_file_mmap,
         .open           = generic_file_open,
         .ioctl          = btrfs_ioctl,
         .fsync          = btrfs_sync_file,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e639cc9e089f..def33ac90d77 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -31,6 +31,7 @@
 #include <linux/writeback.h>
 #include <linux/statfs.h>
 #include <linux/compat.h>
+#include <linux/bit_spinlock.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -561,7 +562,7 @@ static int btrfs_truncate_page(struct address_space *mapping, loff_t from)
                 goto out;
 
         if (!PageUptodate(page)) {
-                ret = mpage_readpage(page, btrfs_get_block);
+                ret = btrfs_readpage(NULL, page);
                 lock_page(page);
                 if (!PageUptodate(page)) {
                         ret = -EIO;
@@ -1257,8 +1258,10 @@ static int btrfs_get_block_lock(struct inode *inode, sector_t iblock,
         path = btrfs_alloc_path();
         BUG_ON(!path);
         if (create & BTRFS_GET_BLOCK_CREATE) {
-                WARN_ON(1);
-                /* this almost but not quite works */
+                /*
+                 * danger!, this only works if the page is properly up
+                 * to date somehow
+                 */
                 trans = btrfs_start_transaction(root, 1);
                 if (!trans) {
                         err = -ENOMEM;
@@ -1353,7 +1356,6 @@ not_found:
                                                ins.objectid, ins.offset,
                                                ins.offset);
                 BUG_ON(ret);
-                SetPageChecked(result->b_page);
                 btrfs_map_bh_to_logical(root, result, ins.objectid);
         }
 out:
@@ -1374,6 +1376,40 @@ int btrfs_get_block(struct inode *inode, sector_t iblock,
         return err;
 }
 
+int btrfs_get_block_csum(struct inode *inode, sector_t iblock,
+                    struct buffer_head *result, int create)
+{
+        int ret;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        struct page *page = result->b_page;
+        u64 offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(result);
+        struct btrfs_csum_item *item;
+        struct btrfs_path *path = NULL;
+
+        mutex_lock(&root->fs_info->fs_mutex);
+        ret = btrfs_get_block_lock(inode, iblock, result, create);
+        if (ret)
+                goto out;
+
+        path = btrfs_alloc_path();
+        item = btrfs_lookup_csum(NULL, root, path, inode->i_ino, offset, 0);
+        if (IS_ERR(item)) {
+                ret = PTR_ERR(item);
+                /* a csum that isn't present is a preallocated region. */
+                if (ret == -ENOENT || ret == -EFBIG)
+                        ret = 0;
+                result->b_private = 0;
+                goto out;
+        }
+        memcpy((char *)&result->b_private, &item->csum, BTRFS_CRC32_SIZE);
+printk("get_block_sum file %lu offset %llu csum %X\n", inode->i_ino, (unsigned long long)offset, *(int *)(&item->csum));
+out:
+        if (path)
+                btrfs_free_path(path);
+        mutex_unlock(&root->fs_info->fs_mutex);
+        return ret;
+}
+
 static int btrfs_get_block_bmap(struct inode *inode, sector_t iblock,
                            struct buffer_head *result, int create)
 {
@@ -1395,9 +1431,198 @@ static int btrfs_prepare_write(struct file *file, struct page *page,
         return block_prepare_write(page, from, to, btrfs_get_block);
 }
 
-static int btrfs_readpage(struct file *file, struct page *page)
+static void buffer_io_error(struct buffer_head *bh)
+{
+        char b[BDEVNAME_SIZE];
+
+        printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
+                        bdevname(bh->b_bdev, b),
+                        (unsigned long long)bh->b_blocknr);
+}
+
+/*
+ * I/O completion handler for block_read_full_page() - pages
+ * which come unlocked at the end of I/O.
+ */
+static void btrfs_end_buffer_async_read(struct buffer_head *bh, int uptodate)
+{
+        unsigned long flags;
+        struct buffer_head *first;
+        struct buffer_head *tmp;
+        struct page *page;
+        int page_uptodate = 1;
+        struct inode *inode;
+        int ret;
+
+        BUG_ON(!buffer_async_read(bh));
+
+        page = bh->b_page;
+        inode = page->mapping->host;
+        if (uptodate) {
+                void *kaddr;
+                struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
+                if (bh->b_private) {
+                        char csum[BTRFS_CRC32_SIZE];
+                        kaddr = kmap_atomic(page, KM_IRQ0);
+                        ret = btrfs_csum_data(root, kaddr + bh_offset(bh),
+                                              bh->b_size, csum);
+                        BUG_ON(ret);
+                        if (memcmp(csum, &bh->b_private, BTRFS_CRC32_SIZE)) {
+                                u64 offset;
+                                offset = (page->index << PAGE_CACHE_SHIFT) +
+                                        bh_offset(bh);
+                                printk("btrfs csum failed ino %lu off %llu\n",
+                                       page->mapping->host->i_ino,
+                                       (unsigned long long)offset);
+                                memset(kaddr + bh_offset(bh), 1, bh->b_size);
+                                flush_dcache_page(page);
+printk("bad verify file %lu offset %llu bh_private %lX csum %X\n", inode->i_ino, (unsigned long long)offset, (unsigned long)(bh->b_private), *(int *)csum);
+                        }
+                        kunmap_atomic(kaddr, KM_IRQ0);
+                }
+                set_buffer_uptodate(bh);
+        } else {
+                clear_buffer_uptodate(bh);
+                if (printk_ratelimit())
+                        buffer_io_error(bh);
+                SetPageError(page);
+        }
+
+        /*
+         * Be _very_ careful from here on. Bad things can happen if
+         * two buffer heads end IO at almost the same time and both
+         * decide that the page is now completely done.
+         */
+        first = page_buffers(page);
+        local_irq_save(flags);
+        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
+        clear_buffer_async_read(bh);
+        unlock_buffer(bh);
+        tmp = bh;
+        do {
+                if (!buffer_uptodate(tmp))
+                        page_uptodate = 0;
+                if (buffer_async_read(tmp)) {
+                        BUG_ON(!buffer_locked(tmp));
+                        goto still_busy;
+                }
+                tmp = tmp->b_this_page;
+        } while (tmp != bh);
+        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+        local_irq_restore(flags);
+
+        /*
+         * If none of the buffers had errors and they are all
+         * uptodate then we can set the page uptodate.
+         */
+        if (page_uptodate && !PageError(page))
+                SetPageUptodate(page);
+        unlock_page(page);
+        return;
+
+still_busy:
+        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+        local_irq_restore(flags);
+        return;
+}
+
+/*
+ * Generic "read page" function for block devices that have the normal
+ * get_block functionality. This is most of the block device filesystems.
+ * Reads the page asynchronously --- the unlock_buffer() and
+ * set/clear_buffer_uptodate() functions propagate buffer state into the
+ * page struct once IO has completed.
+ */
+int btrfs_readpage(struct file *file, struct page *page)
 {
-        return mpage_readpage(page, btrfs_get_block);
+        struct inode *inode = page->mapping->host;
+        sector_t iblock, lblock;
+        struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+        unsigned int blocksize;
+        int nr, i;
+        int fully_mapped = 1;
+
+        BUG_ON(!PageLocked(page));
+        blocksize = 1 << inode->i_blkbits;
+        if (!page_has_buffers(page))
+                create_empty_buffers(page, blocksize, 0);
+        head = page_buffers(page);
+
+        iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
+        lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
+        bh = head;
+        nr = 0;
+        i = 0;
+
+        do {
+                if (buffer_uptodate(bh))
+                        continue;
+
+                if (!buffer_mapped(bh)) {
+                        int err = 0;
+
+                        fully_mapped = 0;
+                        if (iblock < lblock) {
+                                WARN_ON(bh->b_size != blocksize);
+                                err = btrfs_get_block_csum(inode, iblock,
+                                                           bh, 0);
+                                if (err)
+                                        SetPageError(page);
+                        }
+                        if (!buffer_mapped(bh)) {
+                                void *kaddr = kmap_atomic(page, KM_USER0);
+                                memset(kaddr + i * blocksize, 0, blocksize);
+                                flush_dcache_page(page);
+                                kunmap_atomic(kaddr, KM_USER0);
+                                if (!err)
+                                        set_buffer_uptodate(bh);
+                                continue;
+                        }
+                        /*
+                         * get_block() might have updated the buffer
+                         * synchronously
+                         */
+                        if (buffer_uptodate(bh))
+                                continue;
+                }
+                arr[nr++] = bh;
+        } while (i++, iblock++, (bh = bh->b_this_page) != head);
+
+        if (fully_mapped)
+                SetPageMappedToDisk(page);
+
+        if (!nr) {
+                /*
+                 * All buffers are uptodate - we can set the page uptodate
+                 * as well. But not if get_block() returned an error.
+                 */
+                if (!PageError(page))
+                        SetPageUptodate(page);
+                unlock_page(page);
+                return 0;
+        }
+
+        /* Stage two: lock the buffers */
+        for (i = 0; i < nr; i++) {
+                bh = arr[i];
+                lock_buffer(bh);
+                bh->b_end_io = btrfs_end_buffer_async_read;
+                set_buffer_async_read(bh);
+        }
+
+        /*
+         * Stage 3: start the IO.  Check for uptodateness
+         * inside the buffer lock in case another process reading
+         * the underlying blockdev brought it uptodate (the sct fix).
+         */
+        for (i = 0; i < nr; i++) {
+                bh = arr[i];
+                if (buffer_uptodate(bh))
+                        btrfs_end_buffer_async_read(bh, 1);
+                else
+                        submit_bh(READ, bh);
+        }
+        return 0;
 }
 
 /*
@@ -1424,6 +1649,7 @@ static int __btrfs_write_full_page(struct inode *inode, struct page *page,
         struct buffer_head *bh, *head;
         const unsigned blocksize = 1 << inode->i_blkbits;
         int nr_underway = 0;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
 
         BUG_ON(!PageLocked(page));
 
@@ -1496,6 +1722,24 @@ static int __btrfs_write_full_page(struct inode *inode, struct page *page,
                         continue;
                 }
                 if (test_clear_buffer_dirty(bh) && bh->b_blocknr != 0) {
+                        struct btrfs_trans_handle *trans;
+                        int ret;
+                        u64 off = page->index << PAGE_CACHE_SHIFT;
+                        char *kaddr;
+
+                        off += bh_offset(bh);
+                        mutex_lock(&root->fs_info->fs_mutex);
+                        trans = btrfs_start_transaction(root, 1);
+                        btrfs_set_trans_block_group(trans, inode);
+                        kaddr = kmap(page);
+                        ret = btrfs_csum_file_block(trans, root, inode->i_ino,
+                                                    off, kaddr + bh_offset(bh),
+                                                    bh->b_size);
+                        kunmap(page);
+                        BUG_ON(ret);
+                        ret = btrfs_end_transaction(trans, root);
+                        BUG_ON(ret);
+                        mutex_unlock(&root->fs_info->fs_mutex);
                         mark_buffer_async_write(bh);
                 } else {
                         unlock_buffer(bh);
@@ -1617,6 +1861,53 @@ static int btrfs_writepage(struct page *page, struct writeback_control *wbc)
         return __btrfs_write_full_page(inode, page, wbc);
 }
 
+/*
+ * btrfs_page_mkwrite() is not allowed to change the file size as it gets
+ * called from a page fault handler when a page is first dirtied. Hence we must
+ * be careful to check for EOF conditions here. We set the page up correctly
+ * for a written page which means we get ENOSPC checking when writing into
+ * holes and correct delalloc and unwritten extent mapping on filesystems that
+ * support these features.
+ *
+ * We are not allowed to take the i_mutex here so we have to play games to
+ * protect against truncate races as the page could now be beyond EOF.  Because
+ * vmtruncate() writes the inode size before removing pages, once we have the
+ * page lock we can determine safely if the page is beyond EOF. If it is not
+ * beyond EOF, then the page is guaranteed safe against truncation until we
+ * unlock the page.
+ */
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+{
+        struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+        unsigned long end;
+        loff_t size;
+        int ret = -EINVAL;
+
+        lock_page(page);
+        wait_on_page_writeback(page);
+printk("btrfs_page_mkwrite %lu %lu\n", page->mapping->host->i_ino, page->index);
+        size = i_size_read(inode);
+        if ((page->mapping != inode->i_mapping) ||
+            ((page->index << PAGE_CACHE_SHIFT) > size)) {
+                /* page got truncated out from underneath us */
+                goto out_unlock;
+        }
+
+        /* page is wholly or partially inside EOF */
+        if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
+                end = size & ~PAGE_CACHE_MASK;
+        else
+                end = PAGE_CACHE_SIZE;
+
+        ret = btrfs_prepare_write(NULL, page, 0, end);
+        if (!ret)
+                ret = btrfs_commit_write(NULL, page, 0, end);
+
+out_unlock:
+        unlock_page(page);
+        return ret;
+}
+
 static void btrfs_truncate(struct inode *inode)
 {
         struct btrfs_root *root = BTRFS_I(inode)->root;