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Date:   Wed, 10 May 2023 18:00:18 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     youling 257 <youling257@gmail.com>, jack@suse.cz,
        hch@infradead.org, hch@lst.de, linux-ext4@vger.kernel.org,
        ritesh.list@gmail.com, keescook@chromium.org
Subject: Re: [PATCH v4 12/13] ext4: Stop providing .writepage hook
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On Tue, May 09, 2023 at 11:50:36PM -0700, Eric Biggers wrote:
> On Wed, May 10, 2023 at 01:47:58PM +0800, youling 257 wrote:
> > I do more test, it is android esdfs or sdcardfs
> > /storage/emulated/0/Android/data problem,
> > "ext4: Stop providing .writepage hook" cause
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.0
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.1
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.idx
> > unable read,
> > 
> > on linux 6.4, i use mount bind data/media on storage/emulated, chmod
> > -R 0777 /data/media/0, rm
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/*, open
> > gallery app can read pictures thumbnail,
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.idx
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.0
> > /storage/emulated/0/Android/data/com.android.gallery3d/cache/imgcache.1
> > available read.
> 
> Maybe try reverting your commit that added esdfs to your kernel?  It should not
> be needed at all.

Youling, what version of Android are you trying to run with the latest
bleeding edge kernel?  Starting with Android 11, sdcardfs was
deprecated[1].

    SDCardFS is deprecated on devices that launch with Android 11 or
    higher and run kernel version 5.4 or higher. On such devices, VTS
    testing doesn't allow mounted file systems listed as
    SDCardFS. Devices that launch with Android 11 or higher but run
    kernel version 4.19 or lower can continue to use SDCardFS, but
    Google doesn't provide additional support.

[1] https://source.android.com/docs/core/storage/sdcardfs-deprecate

With newer versions of Android, use of something like sdcardfs or
esdfs is not necessary.  If you are using an older version of Android,
and you insist on use a bleeding edge kernel where the writepage is
getting deprecated, then someone will need to update esdfs or deal
with the changing internal interfaces of the upstream kernel.  This is
not the ext4 upstream developer's problem.

Personally, I would recommend that you *not* try to fix esdfs; that's
because stacking file systems like sdcardfs and esdfs are inherently
unreliable.   See the section in [1] entitled, "Why deprecate sdcardfs?".

Instead, what I would recommend is upgrading to a newer version of
Android, and then dropping esdfs from your kernel repository.

	     	  	   	      	   	  - Ted