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Subject[PATCH 1/3] bdi: Use parent filesystem BDI for inodes not capable of writeback
Date
If inode->i_mapping->backing_dev_info is not capable of writeback
but the inode gets dirty (because inode itself has changed), use
inode lists of a bdi of a filesystem holding the device inode.
Forking the flusher thread just to do the writeout of a single
inode would be silly and generally bdi needn't be prepared to do
any writeback.

This is part of fixing a bug
https://bugzilla.kernel.org/show_bug.cgi?id=16312.

Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/fs-writeback.c | 17 +++++++++++++++--
1 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index d5be169..00865aa 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -28,8 +28,6 @@
#include <linux/buffer_head.h>
#include "internal.h"

-#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
-
/*
* We don't actually have pdflush, but this one is exported though /proc...
*/
@@ -50,6 +48,21 @@ struct wb_writeback_work {
struct completion *done; /* set if the caller waits */
};

+static struct backing_dev_info *inode_to_bdi(struct inode *inode)
+{
+ struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;
+
+ /*
+ * This is a hack but it solves a problem with device inode
+ * for e.g. /dev/zero getting dirty (via touch or so) and confusing
+ * writeback code. In such cases we return the "parent" filesystem's
+ * bdi.
+ */
+ if (bdi_cap_writeback_dirty(bdi))
+ return bdi;
+ return inode->i_sb->s_bdi;
+}
+
/**
* writeback_in_progress - determine whether there is writeback in progress
* @bdi: the device's backing_dev_info structure.
--
1.6.4.2


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