linux-kernel - Re: [PATCH v2 5/5] nfs: don't clear STATX_ATIME from result

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Date:   Fri, 19 Oct 2018 22:48:35 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Trond Myklebust <trondmy@...merspace.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amir73il@...il.com" <amir73il@...il.com>,
        "mszeredi@...hat.com" <mszeredi@...hat.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "adilger@...ger.ca" <adilger@...ger.ca>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "fw@...eb.enyo.de" <fw@...eb.enyo.de>,
        "mtk.manpages@...il.com" <mtk.manpages@...il.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] nfs: don't clear STATX_ATIME from result_mask

On Fri, Oct 19, 2018 at 8:14 PM, Trond Myklebust
<trondmy@...merspace.com> wrote:
> On Fri, 2018-10-19 at 19:46 +0200, Miklos Szeredi wrote:

>> How is it then that only STATX_ATIME is cleared and not the other
>> fields?
>
> It isn't just the atime. We can also fail to revalidate the ctime and
> mtime if they are not being requested by the user.
>
>>
>> Note: junk != stale.  The statx definition doesn't talk about the
>> fields being up-to-date, except for AT_STATX_FORCE_SYNC, so stale
>> attributes are okay, and do not warrant clearing the result_mask.
>>
>
> I disagree. stale == junk here, because the default of
> AT_STATX_SYNC_AS_STAT is described by the manpage as "Do  whatever
> stat(2) does." which this is not.

Ah, you are talking about this:

    /* Is the user requesting attributes that might need revalidation? */
    if (!(request_mask & (STATX_MODE|STATX_NLINK|STATX_ATIME|STATX_CTIME|
                    STATX_MTIME|STATX_UID|STATX_GID|
                    STATX_SIZE|STATX_BLOCKS)))
        goto out_no_update;

Well, if this is triggered for statx(...,  STATX_ATIME,
AT_STATX_SYNC_AS_STAT) and MNT_NOATIME, then yes, result will be junk.
Which means that the code is wrong, it shouldn't do that.

Otherwise (if something other than STATX_ATIME or STATX_INO or
STATX_TYPE is given as well) it *will* do the same thing as what
stat(2) does, so in that case STATX_ATIME should not  be cleared (yet
it is cleared).

I can do a patch, but not tonight...

Thanks,
Miklos


Thanks,
Miklos