linux-kernel - Re: Subject: [RFC PATCH v2 0/8] staging: apfs: init APFS filesystem support

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Message-Id: <47721ba1-2ffb-45df-aed0-ad0308f6d606@app.fastmail.com>
Date: Thu, 15 May 2025 18:00:34 +0200
From: "Sven Peter" <sven@...npeter.dev>
To: "Nick Chan" <towinchenmi@...il.com>,
 Ernesto A. Fernández <ernesto.mnd.fernandez@...il.com>
Cc: "Yangtao Li" <frank.li@...o.com>,
 "Ethan Carter Edwards" <ethan@...ancedwards.com>, asahi@...ts.linux.dev,
 brauner@...nel.org, dan.carpenter@...aro.org,
 "ernesto@...ellium.com" <ernesto@...ellium.com>,
 "Aditya Garg" <gargaditya08@...e.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, jack@...e.cz,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-staging@...ts.linux.dev, "Theodore Ts'o" <tytso@....edu>,
 viro@...iv.linux.org.uk, willy@...radead.org, slava@...eyko.com,
 glaubitz@...sik.fu-berlin.de
Subject: Re: Subject: [RFC PATCH v2 0/8] staging: apfs: init APFS filesystem support

On Thu, May 15, 2025, at 07:08, Nick Chan wrote:
> Ernesto A. Fernández 於 2025/5/15 凌晨4:19 寫道:
>> Hi Nick,
>>
>> On Tue, May 13, 2025 at 12:13:23PM +0800, Nick Chan wrote:
>>> 2. When running Linux on iPhone, iPad, iPod touch, Apple TV (currently there are Apple A7-A11 SoC support in
>>> upstream), resizing the main APFS volume is not feasible especially on A11 due to shenanigans with the encrypted
>>> data volume. So the safe ish way to store a file system on the disk becomes a using linux-apfs-rw on a (possibly
>>> fixed size) volume that only has one file and that file is used as a loopback device.
>> That's very interesting. Fragmentation will be brutal after a while though.
>> Unless you are patching away the copy-on-write somehow?'
> On a fixed size (preallocated size == max size) volume with only a 
> single non-sparse file on it,
> copy-on-write should not happen. I believe the xART volume is also the 
> same case with only
> one non-sparse file.

Yeah, the gigalocker file on the xART volume (which is the only file we care about
for eventual Secure Enclave support on M1+ macs) is stored contiguously without
copy-on-write on the disk.

Sven