linux-kernel - Re: [PATCH v9 06/21] cachefiles: enable on-demand read mode

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Message-ID: <a79e09a0-16d2-4d73-af9f-05a259431040@linux.alibaba.com>
Date:   Thu, 21 Apr 2022 23:11:43 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, xiang@...nel.org, chao@...nel.org,
        linux-erofs@...ts.ozlabs.org, torvalds@...ux-foundation.org,
        gregkh@...uxfoundation.org, willy@...radead.org,
        linux-fsdevel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        bo.liu@...ux.alibaba.com, tao.peng@...ux.alibaba.com,
        gerry@...ux.alibaba.com, eguan@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, luodaowen.backend@...edance.com,
        tianzichen@...ishou.com, fannaihao@...du.com,
        zhangjiachen.jaycee@...edance.com
Subject: Re: [PATCH v9 06/21] cachefiles: enable on-demand read mode

On 4/21/22 10:17 PM, David Howells wrote:
> Jeffle Xu <jefflexu@...ux.alibaba.com> wrote:
> 
>> +	if (IS_ENABLED(CONFIG_CACHEFILES_ONDEMAND) &&
>> +	    !strcmp(args, "ondemand")) {
>> +		set_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags);
>> +	} else if (*args) {
>> +		pr_err("'bind' command doesn't take an argument\n");
> 
> The error message isn't true if CONFIG_CACHEFILES_ONDEMAND=y.  It would be
> better to say "Invalid argument to the 'bind' command".

Right. Or users may gets confused then. Will be fixed in the next version.

> 
>> -retry:
>>  	/* If the caller asked us to seek for data before doing the read, then
>>  	 * we should do that now.  If we find a gap, we fill it with zeros.
>>  	 */
>> @@ -120,16 +119,6 @@ static int cachefiles_read(struct netfs_cache_resources *cres,
>>  			if (read_hole == NETFS_READ_HOLE_FAIL)
>>  				goto presubmission_error;
>>  
>> -			if (read_hole == NETFS_READ_HOLE_ONDEMAND) {
>> -				ret = cachefiles_ondemand_read(object, off, len);
>> -				if (ret)
>> -					goto presubmission_error;
>> -
>> -				/* fail the read if no progress achieved */
>> -				read_hole = NETFS_READ_HOLE_FAIL;
>> -				goto retry;
>> -			}
>> -
> 

Sorry, it's my mistake when doing "git rebase". The previous version
(v8) actually calls cachefiles_ondemand_read() in cachefiles_read().
However as explained in the commit message of patch 5 ("cachefiles:
implement on-demand read"), fscache_read() can only detect if the
requested file range is fully cache miss, whilst it can't detect if it
is partial cache miss, i.e. there's a hole inside the requested file range.

Thus in this patchset (v9), we move the entry of calling
cachefiles_ondemand_read() from cachefiles_read() to
cachefiles_prepare_read(). The above "deletion of newly added code" is
actually reverting the previous change to cachefiles_read(). It was
mistakenly merged to this patch when I was doing "git rebase"...
Actually it should be merged to patch 5 ("cachefiles: implement
on-demand read"), which initially introduce the change to cachefiles_read().

Apologize for the careless mistake...

-- 
Thanks,
Jeffle