Re: [PATCH] mm, fadvise: don't return -EINVAL when filesystem has no optimization way

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

(6/20/12 2:31 AM), Wanlong Gao wrote:
> On 06/16/2012 04:36 AM, kosaki.motohiro@gmail.com wrote:
>> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>>
>> Eric Wong reported his test suite was fail when /tmp is tmpfs.
>>
>> https://lkml.org/lkml/2012/2/24/479
>>
>> Current,input check of POSIX_FADV_WILLNEED has two problems.
>>
>> 1) require a_ops->readpage.
>>    But in fact, force_page_cache_readahead() only require
>>    a target filesystem has either ->readpage or ->readpages.
>> 2) return -EINVAL when filesystem don't have ->readpage.
>>    But, posix says, it should be retrieved a hint. Thus fadvise()
>>    should return 0 if filesystem has no optimization way.
>>    Especially, userland application don't know a filesystem type
>>    of TMPDIR directory as Eric pointed out. Then, userland can't
>>    avoid this error. We shouldn't encourage to ignore syscall
>>    return value.
>>
>> Thus, this patch change a return value to 0 when filesytem don't
>> support readahead.
>>
>> Cc: linux-mm@kvack.org
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Hillf Danton <dhillf@gmail.com>
>> Signed-off-by: Eric Wong <normalperson@yhbt.net>
>> Tested-by: Eric Wong <normalperson@yhbt.net>
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> ---
>>  mm/fadvise.c |   18 +++++++-----------
>>  1 files changed, 7 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/fadvise.c b/mm/fadvise.c
>> index 469491e..33e6baf 100644
>> --- a/mm/fadvise.c
>> +++ b/mm/fadvise.c
>> @@ -93,11 +93,6 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
>>  		spin_unlock(&file->f_lock);
>>  		break;
>>  	case POSIX_FADV_WILLNEED:
>> -		if (!mapping->a_ops->readpage) {
>> -			ret = -EINVAL;
>> -			break;
>> -		}
> 
> Why not check both readpage and readpages, if they are not here,
> just beak and no following force_page_cache_readahead ?

They are checked in force_page_cache_readahead.