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Thu, 05 Mar 2026 01:32:38 -0800 (PST) Message-ID: <9078e07d-5997-41f3-9991-c1f6975c768b@gmail.com> Date: Thu, 5 Mar 2026 17:32:36 +0800 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Anand Jain Subject: Re: [PATCH 0/3] fix s_uuid and f_fsid consistency for cloned filesystems To: Christoph Hellwig , Anand Jain Cc: linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org References: Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/3/26 21:28, Christoph Hellwig wrote: > On Thu, Feb 26, 2026 at 10:23:32PM +0800, Anand Jain wrote: >> This series resolves the tradeoff by aligning btrfs and ext4 behaviour >> with XFS: f_fsid incorporates device identity (devt) to remain unique >> across clones, while s_uuid is preserved consistently matching the on-disk >> uuid. > > While I like fixing this up, switching the f_fsid construction to a > different method might break things. Is there a way to only change > it for cloned file systems to reduce the surface of this change? The problem is that we won't know which filesystem is the original and which is the clone. Generally, the first one mounted is treated as the original and the following one as the clone. However, f_fsid should remain consistent regardless of mount order, at least for the duration that the block device is connected (or until a system reboot). >> Patches >> ------- >> Patch 1/3: btrfs: fix f_fsid to include rootid and devt >> Patch 2/3: btrfs: fix s_uuid to be stable across mounts for cloned filesystems >> Patch 3/3: ext4: fix f_fsid to use devt instead of s_uuid > > I don't really see that patch 3 in my inbox on linux-btrfs. My bad, I sent the btrfs/ext4 patches only to their respective mailing lists. I'll copy both in v2. Here it is: https://lore.kernel.org/linux-ext4/e269a49eed2de23eb9f9bd7f506f0fe47696a023.1772095546.git.asj@kernel.org/ Thanks, Anand