Re: [PATCH v2] btrfs: use IOMAP_DIO_BOUNCE flag instead of falling back to buffered IO

[Christoph Hellwig <hch@infradead.org>]

On Mon, May 25, 2026 at 04:46:16PM +0930, Qu Wenruo wrote:
> > > +	if (!(inode->flags & BTRFS_INODE_NODATASUM) ||
> > > +	    (data_profile != BTRFS_BLOCK_GROUP_RAID0 && data_profile != 0))
> > 
> > Should the 0 here be BTRFS_RAID_SINGLE for better documentation?
> 
> That BTRFS_RAID_SINGLE is a special enum for iterating btrfs_raid_array[].
> 
> Meanwhile for bit flags we do not use that enum index, even if the values
> match.

Ok.

> > 
> > Also the old code only did this for !BTRFS_INODE_NODATASUM and not
> > raid, right?
> 
> The old code also does the fallback to buffered for raid too.
> 
> That's done in commit 7c2830f00c3e ("btrfs: fallback to buffered IO if the
> data profile has duplication").

Ah, right.

> > Also while you touch this, you should probably also check the
> > bdev_stable_writes similar to XFS (probably yet another patch).
> 
> For btrfs stable writes == data csum so far. But we do not have any bdev
> stable writes checks, thus it will be a pretty huge change if we want to
> take per-dev stable writes into consideration.

I tink you need to.  Various network storage protocols like iSCSI, NVMe
over fabrics or DRBD, as well as T10 data protection for SCSI and NVMe
require stable pages, so you have to take them into account.  My
approach would be to do it globally if any such device is part of the
pool.