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

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 06/20/2012 02:33 PM, KOSAKI Motohiro wrote:
> (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.

I see, thank you.

Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>


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