linux-ext4 - Re: [man-pages RFC PATCH] statx.2, open.2: document STATX

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Date:   Thu, 23 Jun 2022 10:13:34 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-man@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-xfs@...r.kernel.org, linux-api@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Keith Busch <kbusch@...nel.org>
Subject: Re: [man-pages RFC PATCH] statx.2, open.2: document STATX_DIOALIGN

On Thu, Jun 23, 2022 at 10:27:19AM -0600, Andreas Dilger wrote:
> On Jun 23, 2022, at 10:02 AM, Darrick J. Wong <djwong@...nel.org> wrote:
> > 
> > On Thu, Jun 16, 2022 at 01:21:41PM -0700, Eric Biggers wrote:
> >> From: Eric Biggers <ebiggers@...gle.com>
> >> 
> >> @@ -244,8 +249,11 @@ STATX_SIZE	Want stx_size
> >> STATX_BLOCKS	Want stx_blocks
> >> STATX_BASIC_STATS	[All of the above]
> >> STATX_BTIME	Want stx_btime
> >> +STATX_ALL	The same as STATX_BASIC_STATS | STATX_BTIME.
> >> +         	This is deprecated and should not be used.
> > 
> > STATX_ALL is deprecated??  I was under the impression that _ALL meant
> > all the known bits for that kernel release, but...
> 
> For userspace STATX_ALL doesn't make sense, and it isn't used by the kernel.
> 
> Firstly, that would be a compile-time value for an application, so it
> may be incorrect for the kernel the code is actually run on (either too
> many or too few bits could be set).
> 
> Secondly, it isn't really useful for an app to request "all attributes"
> if it doesn't know what they all mean, as that potentially adds useless
> overhead.  Better for it to explicitly request the attributes that it
> needs.  If that is fewer than the kernel could return it is irrelevant,
> since the app would ignore them anyway.
> 
> The kernel will already ignore and mask attributes that *it* doesn't
> understand, so requesting more is fine and STATX_ALL doesn't help this.
> 

What Andreas said.  Note, this discussion really should be happening on my
standalone patch that fixes the documentation for STATX_ALL:
https://lore.kernel.org/r/20220614034459.79889-1-ebiggers@kernel.org.  I folded
it into this RFC one only so that it applies cleanly without a prerequisite.

- Eric