Re: [RFC PATCH 1/2] fs: introduce FALLOC_FL_FORCE_ZERO to fallocate

[Zhang Yi <yi.zhang@huaweicloud.com>]

On 2025/1/6 19:27, Christoph Hellwig wrote:
> There's a feature request for something similar on the xfs list, so
> I guess people are asking for it.
> 
> That being said this really should not be a modifier but a separate
> operation, as the logic is very different from FALLOC_FL_ZERO_RANGE,
> similar to how plain prealloc, hole punch and zero range are different
> operations despite all of them resulting in reads of zeroes from the
> range.

OK, it seems reasonable to me, and adding a new operation would be
better. There is actually no need to mix it with the current
FALLOC_FL_ZERO_RANGE.

> 
> That will also make it more clear that for files or file systems that
> require out place writes this operation should fail instead of doing
> pointless multiple writes.
> 
> Also please write a man page update clearly specifying the semantics,
> especially if this should work or not if there is no write zeroes
> offload in the hardware, or if that offload actually writes physical
> zeroes to the media or not.
> 

Sure. thanks for your advice.

Thanks,
Yi.

> Btw, someone really should clean up the ext4 fallocate code to use
> helper adnd do the
> 
> 	switch (mode & FALLOC_FL_MODE_MASK) {
> 	}
> 
> and then use helpers for each mode whih will make these things a lot
> more obvious.