Hi Erez,
On Sun, 14 Oct 2007, Erez Zadok wrote:
> In unionfs_writepage() I tried to emulate as best possible what the lower
> f/s will have returned to the VFS. Since tmpfs's ->writepage can return
> AOP_WRITEPAGE_ACTIVATE and re-mark its page as dirty, I did the same in
> unionfs: mark again my page as dirty, and return AOP_WRITEPAGE_ACTIVATE.
>
> Should I be doing something different when unionfs stacks on top of tmpfs?
> (BTW, this is probably also relevant to ecryptfs.)
Look at mm/filemap.c:__filemap_fdatawrite_range(). You shouldn't be
calling unionfs_writepage() _at all_ if the lower mapping has
BDI_CAP_NO_WRITEBACK capability set. Perhaps something like the totally
untested patch below?
Pekka
---
fs/unionfs/mmap.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
Index: linux-2.6.23-rc8/fs/unionfs/mmap.c
===================================================================
--- linux-2.6.23-rc8.orig/fs/unionfs/mmap.c
+++ linux-2.6.23-rc8/fs/unionfs/mmap.c
@@ -17,6 +17,7 @@
* published by the Free Software Foundation.
*/
+#include <linux/backing-dev.h>
#include "union.h"
/*
@@ -144,6 +145,21 @@ out:
return err;
}
+static int unionfs_writepages(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ struct inode *lower_inode;
+ struct inode *inode;
+
+ inode = mapping->host;
+ lower_inode = unionfs_lower_inode(inode);
+
+ if (!mapping_cap_writeback_dirty(lower_inode->i_mapping))
+ return 0;
+
+ return generic_writepages(mapping, wbc);
+}
+
/*
* readpage is called from generic_page_read and the fault handler.
* If your file system uses generic_page_read for the read op, it
@@ -371,6 +387,7 @@ 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,
-
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