linux-kernel - Re: [PATCH 2/2] erofs: switch to prepare_ondemand

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Date:   Fri, 4 Nov 2022 20:20:09 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     Jeff Layton <jlayton@...nel.org>, dhowells@...hat.com,
        xiang@...nel.org, chao@...nel.org, linux-cachefs@...hat.com,
        linux-erofs@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/2] erofs: switch to prepare_ondemand_read() in fscache
 mode



On 11/4/22 7:46 PM, Jeff Layton wrote:
> On Fri, 2022-11-04 at 15:26 +0800, Jingbo Xu wrote:
>> Switch to prepare_ondemand_read() interface and a self-contained request
>> completion to get rid of netfs_io_[request|subrequest].
>>
>> The whole request will still be split into slices (subrequest) according
>> to the cache state of the backing file.  As long as one of the
>> subrequests fails, the whole request will be marked as failed. Besides
>> it will not retry for short read.  Similarly the whole request will fail
>> if that really happens. 
>>
> 
> That's sort of nasty. The kernel can generally give you a short read for
> all sorts of reasons, some of which may have nothing to do with the
> underlying file or filesystem.
> 
> Passing an error back to an application on a short read is probably not
> what you want to do here. The usual thing to do is just to return what
> you can, and let the application redrive the request if it wants.
> 

Yeah, thanks for your comment. We can fix this either in current
patchset or a separate series. As we just discussed on IRC, we will fix
in the following series.



-- 
Thanks,
Jingbo