[RFCv2,2/3] block: add helper for setting and clearing S_DAX on inode
diff mbox

Message ID 1463184168-3381-3-git-send-email-jonathan.derrick@intel.com
State New
Headers show

Commit Message

Derrick, Jonathan May 14, 2016, 12:02 a.m. UTC
inode->i_flags locking rules suggest using the i_mutex lock. This patch
adds a helper to do the locking and setting of S_DAX on the block device
inode.

Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
---
 fs/block_dev.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

Comments

Elliott, Robert (Servers) May 14, 2016, 5:05 a.m. UTC | #1
> -----Original Message-----
> From: linux-block-owner@vger.kernel.org [mailto:linux-block-
> owner@vger.kernel.org] On Behalf Of Jon Derrick
> Sent: Friday, May 13, 2016 7:03 PM
...
> Subject: [RFCv2 2/3] block: add helper for setting and clearing S_DAX on
> inode
> 
> inode->i_flags locking rules suggest using the i_mutex lock. This patch
> adds a helper to do the locking and setting of S_DAX on the block device
> inode.
...
> +static void bd_set_dax(struct block_device *bdev, bool enabled)
> +{
> +	struct inode *inode = bdev->bd_inode;
> +
> +	inode_lock(inode);
> +	if (enabled)
> +		inode->i_flags = S_DAX;
> +	else
> +		inode->i_flags &= ~S_DAX;
> +	inode_unlock(inode);
> +}

This is not symmetric - setting wipes out any other bits, but
clearing only clears the S_DAX bit. That seems confusing for
a helper function.

Using |= would be symmetric, but wouldn't replace what 
__blkdev_get does (if what it does is appropriate).

> @@ -1206,9 +1218,9 @@ static int __blkdev_get(struct block_device *bdev,
> fmode_t mode, int for_part)
>  		bdev->bd_queue = disk->queue;
>  		bdev->bd_contains = bdev;
>  		if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops-
> >direct_access)
> -			bdev->bd_inode->i_flags = S_DAX;
> +			bd_set_dax(bdev, 1);
>  		else
> -			bdev->bd_inode->i_flags &= ~S_DAX;
> +			bd_set_dax(bdev, 0);

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Derrick, Jonathan May 16, 2016, 5:31 p.m. UTC | #2
On Sat, May 14, 2016 at 05:05:59AM +0000, Elliott, Robert (Persistent Memory) wrote:
> 
> 
> > -----Original Message-----
> > From: linux-block-owner@vger.kernel.org [mailto:linux-block-
> > owner@vger.kernel.org] On Behalf Of Jon Derrick
> > Sent: Friday, May 13, 2016 7:03 PM
> ...
> > Subject: [RFCv2 2/3] block: add helper for setting and clearing S_DAX on
> > inode
> > 
> > inode->i_flags locking rules suggest using the i_mutex lock. This patch
> > adds a helper to do the locking and setting of S_DAX on the block device
> > inode.
> ...
> > +static void bd_set_dax(struct block_device *bdev, bool enabled)
> > +{
> > +	struct inode *inode = bdev->bd_inode;
> > +
> > +	inode_lock(inode);
> > +	if (enabled)
> > +		inode->i_flags = S_DAX;
> > +	else
> > +		inode->i_flags &= ~S_DAX;
> > +	inode_unlock(inode);
> > +}
> 
> This is not symmetric - setting wipes out any other bits, but
> clearing only clears the S_DAX bit. That seems confusing for
> a helper function.
> 
> Using |= would be symmetric, but wouldn't replace what 
> __blkdev_get does (if what it does is appropriate).
> 
I'm under the impression that S_DAX is the only inode flag appropriate for a block device inode with direct-access, even though it does break the 'flag' semantic.

It does bring up an interesting question about the fate of the block device inode when S_DAX is set and then cleared later due to the two other conditions that can clear S_DAX.

I think the appropriate fix is to save the inode flags when setting DAX and restore them when we need to clear S_DAX.

> > @@ -1206,9 +1218,9 @@ static int __blkdev_get(struct block_device *bdev,
> > fmode_t mode, int for_part)
> >  		bdev->bd_queue = disk->queue;
> >  		bdev->bd_contains = bdev;
> >  		if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops-
> > >direct_access)
> > -			bdev->bd_inode->i_flags = S_DAX;
> > +			bd_set_dax(bdev, 1);
> >  		else
> > -			bdev->bd_inode->i_flags &= ~S_DAX;
> > +			bd_set_dax(bdev, 0);
> 
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Patch
diff mbox

diff --git a/fs/block_dev.c b/fs/block_dev.c
index d4fa725..252e459 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1159,6 +1159,18 @@  void bd_set_size(struct block_device *bdev, loff_t size)
 }
 EXPORT_SYMBOL(bd_set_size);
 
+static void bd_set_dax(struct block_device *bdev, bool enabled)
+{
+	struct inode *inode = bdev->bd_inode;
+
+	inode_lock(inode);
+	if (enabled)
+		inode->i_flags = S_DAX;
+	else
+		inode->i_flags &= ~S_DAX;
+	inode_unlock(inode);
+}
+
 static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part);
 
 /*
@@ -1206,9 +1218,9 @@  static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 		bdev->bd_queue = disk->queue;
 		bdev->bd_contains = bdev;
 		if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops->direct_access)
-			bdev->bd_inode->i_flags = S_DAX;
+			bd_set_dax(bdev, 1);
 		else
-			bdev->bd_inode->i_flags &= ~S_DAX;
+			bd_set_dax(bdev, 0);
 
 		if (!partno) {
 			ret = -ENXIO;
@@ -1239,7 +1251,7 @@  static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			if (!ret) {
 				bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
 				if (!blkdev_dax_capable(bdev))
-					bdev->bd_inode->i_flags &= ~S_DAX;
+					bd_set_dax(bdev, 0);
 			}
 
 			/*
@@ -1276,7 +1288,7 @@  static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			}
 			bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
 			if (!blkdev_dax_capable(bdev))
-				bdev->bd_inode->i_flags &= ~S_DAX;
+				bd_set_dax(bdev, 0);
 		}
 	} else {
 		if (bdev->bd_contains == bdev) {