Message-ID: <CAOzgRdYXOgAM+s6OY=eNdg2oJOOTVO6rq+R+PMA6sLyEfm-OdQ@mail.gmail.com>
Date:   Wed, 10 May 2023 13:47:58 +0800
From:   youling 257 <youling257@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     Eric Biggers <ebiggers@...nel.org>, jack@...e.cz,
        hch@...radead.org, hch@....de, linux-ext4@...r.kernel.org,
        ritesh.list@...il.com, keescook@...omium.org
Subject: Re: [PATCH v4 12/13] ext4: Stop providing .writepage hook

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.


2023-05-10 13:17 GMT+08:00, youling 257 <youling257@...il.com>:
> It isn't android storage emulated esdfs or sdcardfs problem, i test
> mount bind /data/media on /storage/emulated, can reproduce my problem.
> Let me say clear my problem, "ext4: Stop providing .writepage hook"
> cause android gallery app unable read pictures thumbnails.
>
> I test linux kernel 6.3 Revert "ext4: Stop providing .writepage hook",
> android gallery can read pictures thumbnails,
>
> this is mount bind /data/media on /storage/emulated
> /dev/nvme0n1p1 on /storage/emulated type ext4 (rw,seclabel,noatime)
> /dev/nvme0n1p1 on /mnt/runtime/default/emulated type ext4
> (rw,seclabel,noatime)
> /dev/nvme0n1p1 on /mnt/runtime/read/emulated type ext4
> (rw,seclabel,noatime)
> /dev/nvme0n1p1 on /mnt/runtime/write/emulated type ext4
> (rw,seclabel,noatime)
> /dev/nvme0n1p1 on /mnt/runtime/full/emulated type ext4
> (rw,seclabel,noatime)
>
> this is esdfs,
> /data/media on /mnt/runtime/default/emulated type esdfs
> (rw,nosuid,nodev,noexec,noatime,lower=1023:1023:664:775,upper=0:1015:771:771,derive=multi,noconfine,derive_gid,default_normal,unshared_obb)
> /data/media on /storage/emulated type esdfs
> (rw,nosuid,nodev,noexec,noatime,lower=1023:1023:664:775,upper=0:1015:771:771,derive=multi,noconfine,derive_gid,default_normal,unshared_obb)
> /data/media on /mnt/runtime/read/emulated type esdfs
> (rw,nosuid,nodev,noexec,noatime,lower=1023:1023:664:775,upper=0:9997:750:750,derive=multi,noconfine,derive_gid,default_normal,unshared_obb)
> /data/media on /mnt/runtime/write/emulated type esdfs
> (rw,nosuid,nodev,noexec,noatime,lower=1023:1023:664:775,upper=0:9997:770:770,derive=multi,noconfine,derive_gid,default_normal,unshared_obb)
> /data/media on /mnt/runtime/full/emulated type esdfs
> (rw,nosuid,nodev,noexec,noatime,lower=1023:1023:664:775,upper=0:9997:770:770,derive=multi,noconfine,derive_gid,default_normal,unshared_obb)
>
> if i do mount bind data/media on storage/emulated, take a screenshot,
> will create
> /data/media/0/Pictures/Screenshots/Screenshot_20230510-130020.png
> file,
> chmod -R 0777 /data/media/0/Pictures/Screenshots,
> on linux 6.3 Revert "ext4: Stop providing .writepage hook", android
> gallery app can read
> /storage/emulated/0/Pictures/Screenshots/Screenshot_20230510-130020.png
> thumbnail,
> linux 6.4 removed .writepage hook, android gallery unable read thumbnail.
>
>
> 2023-05-10 2:36 GMT+08:00, Theodore Ts'o <tytso@....edu>:
>> On Mon, May 08, 2023 at 10:02:27PM -0700, Eric Biggers wrote:
>>> On Tue, May 09, 2023 at 01:51:08AM +0800, youling257 wrote:
>>> > I using linux mainline kernel on android.
>>> > https://github.com/youling257/android-mainline/commits/6.4
>>> > https://github.com/youling257/android-mainline/commits/6.3
>>> > "ext4: Stop providing .writepage hook" cause some android app unable
>>> > to
>>> > read storage/emulated/0 files, i need to say android esdfs file system
>>> > storage/emulated is ext4 data/media bind mount.
>>> > I want to ask, why android storage/emulated need .writepage hook?
>>>
>>> "esdfs" doesn't exist upstream, so linux-ext4 can't provide support for
>>> it.
>>>
>>> Also, it doesn't exist in the Android Common Kernels either, so the
>>> Android team
>>> cannot help you either.
>>
>> The problem with esdfs is that it's based on the old stackable file
>> system paradigm which is filled with races and is inherently
>> unreliable (just for fun, try running fsstress on the upper and lower
>> file systems of a stackable file system simultaneously, and watch the
>> kernel crash and burn).  For that reason, some number of us have been
>> working for a while to eliminate the need for stacking file systems,
>> such as sdcardfs. esdfs, etc. from the Android kernel.
>>
>> The other thing I would add is that upstream has been working[1] on
>> getting rid of writepage function.  So out-of-tree file systems are
>> going to need to adapt --- or die.
>>
>> [1] https://lore.kernel.org/all/20221202102644.770505-1-hch@lst.de/
>>
>> It looks like esdfs is coming from the Chromium kernel?  The latest
>> Chromium kernel I can find is 5.15 based, and it has esdfs in it.  I'm
>> sad to see that esdfs hasn't been removed from the Chromium kernel
>> yet, and replaced with something more stable and reliable, but maybe
>> we can find someone who is more familiar with the Chromium kernel to
>> comment.
>>
>> Cheers,
>>
>> 						- Ted
>>
>

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