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

Christoph Hellwig
2025-01-07T06:10:17Z

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?