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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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