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    Subject[PATCH 3/7] mm: Provide stub page_mkwrite functionality to stabilize pages during writes
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    For filesystems that do not provide any page_mkwrite handler, provide a stub
    page_mkwrite function that locks the page and waits for pending writeback to
    complete. This is needed to stabilize pages during writes for a large variety
    of filesystem drivers (ext2, ext3, vfat, hfs...).

    Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
    ---
    mm/filemap.c | 19 +++++++++++++++++++
    1 files changed, 19 insertions(+), 0 deletions(-)


    diff --git a/mm/filemap.c b/mm/filemap.c
    index fd0e7f2..1e096a0 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1713,8 +1713,27 @@ page_not_uptodate:
    }
    EXPORT_SYMBOL(filemap_fault);

    +static int empty_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
    +{
    + struct page *page = vmf->page;
    + struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
    + loff_t size;
    +
    + lock_page(page);
    + size = i_size_read(inode);
    + if ((page->mapping != inode->i_mapping) ||
    + (page_offset(page) > size)) {
    + /* page got truncated out from underneath us */
    + unlock_page(page);
    + return VM_FAULT_NOPAGE;
    + }
    + wait_on_page_writeback(page);
    + return VM_FAULT_LOCKED;
    +}
    +
    const struct vm_operations_struct generic_file_vm_ops = {
    .fault = filemap_fault,
    + .page_mkwrite = empty_page_mkwrite,
    };

    /* This is used for a general mmap of a disk file */


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