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Subject[PATCH 3/9] Unionfs: support lower filesystems without writeback capability
Date
Implement unionfs_writepages.  As per
mm/filemap.c:__filemap_fdatawrite_range(), don't call our writepage if the
lower mapping has BDI_CAP_NO_WRITEBACK capability set.

Signed-off-by: Pekka J Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
---
fs/unionfs/mmap.c | 23 +++++++++++++++++++++++
fs/unionfs/union.h | 1 +
2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
index 6440282..b43557e 100644
--- a/fs/unionfs/mmap.c
+++ b/fs/unionfs/mmap.c
@@ -144,6 +144,28 @@ out:
return err;
}

+static int unionfs_writepages(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ int err = 0;
+ struct inode *lower_inode;
+ struct inode *inode;
+
+ inode = mapping->host;
+ lower_inode = unionfs_lower_inode(inode);
+ BUG_ON(!lower_inode);
+
+ if (!mapping_cap_writeback_dirty(lower_inode->i_mapping))
+ goto out;
+
+ /* Note: generic_writepages may return AOP_WRITEPAGE_ACTIVATE */
+ err = generic_writepages(mapping, wbc);
+ if (err == 0)
+ unionfs_copy_attr_times(inode);
+out:
+ return err;
+}
+
/*
* readpage is called from generic_page_read and the fault handler.
* If your file system uses generic_page_read for the read op, it
@@ -374,6 +396,7 @@ out:

struct address_space_operations unionfs_aops = {
.writepage = unionfs_writepage,
+ .writepages = unionfs_writepages,
.readpage = unionfs_readpage,
.prepare_write = unionfs_prepare_write,
.commit_write = unionfs_commit_write,
diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
index 8eb2ee4..6333488 100644
--- a/fs/unionfs/union.h
+++ b/fs/unionfs/union.h
@@ -45,6 +45,7 @@
#include <linux/log2.h>
#include <linux/poison.h>
#include <linux/mman.h>
+#include <linux/backing-dev.h>

#include <asm/system.h>

--
1.5.2.2
-
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