Re: [PATCH 4/4] xfs: report the correct read/write dio alignment for reflinked inodes

[Christoph Hellwig <hch@lst.de>]

On Mon, Jan 06, 2025 at 06:37:06PM +0000, John Garry wrote:
>> +	/*
>> +	 * On COW inodes we are forced to always rewrite an entire file system
>> +	 * block or RT extent.
>> +	 *
>> +	 * Because applications assume they can do sector sized direct writes
>> +	 * on XFS we fall back to buffered I/O for sub-block direct I/O in that
>> +	 * case.  Because that needs to copy the entire block into the buffer
>> +	 * cache it is highly inefficient and can easily lead to page cache
>> +	 * invalidation races.
>> +	 *
>> +	 * Tell applications to avoid this case by reporting the natively
>> +	 * supported direct I/O read alignment.
>
> Maybe I mis-read the complete comment, but did you really mean "natively 
> supported direct I/O write alignment"? You have been talking about writes 
> only, but then finally mention read alignment.

No, this is indeed intended to talk about the different (smaller) read
alignment we are now reporting.  But I guess the wording is confusing
enough that I should improve it?