Re: [PATCH 1/3] bdi: Use parent filesystem BDI for inodes notcapable of writeback

From: Christoph Hellwig
Date: Thu Jul 29 2010 - 04:12:22 EST

Given that we only need the per-mapping one for the bdev fs what about

* Return the writeback-relevant backing device for this inode.
* For a normal filesystem this must always be the bdi hanging off the
* superblock, given that we only expect one bdi per filesystems in
* the per-superblock sync functions. But the block device special
* filesystem requires a quick given that it contains the internal
* I/O inodes for block devices on a single superblock. This works
* because the block deevice filesystem inodes are never user visible
* and we will never do a per-superblock sync on it.
static struct backing_dev_info *inode_to_bdi(struct inode *inode)
if (inode->i_sb == blockdev_superblock)
return inode->i_mapping->backing_dev_info;
return inode->i_sb->s_bdi;

that also avoids the need for doing the bdi capabilities audit ASAP.
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