From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout01.posteo.de (mout01.posteo.de [185.67.36.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 726502FFFA8 for ; Tue, 23 Dec 2025 12:08:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.67.36.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766491696; cv=none; b=kUpe0qH6yuex9SAqKp/x4cy2mYP/bgeGZEwyIoj4f4NDU/vN92g2M7ZUVbQxcHUcb727kI3fkM9NVPhAfxDbBRCCwnFRvnSUrFSacjWH9mWX3ru0z7rO9lOadnF0Ei8F7eo5Tt+rstRZ3Q4ZayEuagpiXYqhOcbnvC4CCB6NnIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766491696; c=relaxed/simple; bh=iLKgAKwS4/q2UG56gMDpyTmyrdHKgWrM0cT+xrJm3Qo=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=kRdH8WBdpUKsVF4CX003FH3sPSQT5mNo0QAqV8vZ3wUaWYqV6wYgEJIdbJybPEKUec1LZCf9RkdEH2qbxY8opAnJlBlzsuj2UCvA/83081+CpeM+Gxl67ik/MWn+EjW7C8EI2gOWe5PBC+B/tdSfSvYwlex0Q6onELMckLLu6pk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.net; spf=pass smtp.mailfrom=posteo.net; dkim=pass (2048-bit key) header.d=posteo.net header.i=@posteo.net header.b=JuYFcl8f; arc=none smtp.client-ip=185.67.36.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=posteo.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=posteo.net header.i=@posteo.net header.b="JuYFcl8f" Received: from submission (posteo.de [185.67.36.169]) by mout01.posteo.de (Postfix) with ESMTPS id 30FD4240028 for ; Tue, 23 Dec 2025 13:08:05 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=posteo.net; s=2017; t=1766491685; bh=cqi8Mtl6BSHF6nAD2HUfAsqLFQxO6uHoI1t5KNiy3zo=; h=MIME-Version:Date:From:To:Cc:Subject:Message-ID:Content-Type: Content-Transfer-Encoding:From; b=JuYFcl8fnxIHiQ0tTw1tznXhqey/mE4+kNw9cqULxQ2gqVvqFFxcqCoWkaXOv/zDp gq7IPbpnh0Q1uARFHwkxahJEQPinURNhSMpwH4A7mfBj4zU40NqceWy2sR0uSIm5zf MPyb1EGjlMjCVgP2K1i38RP+5FOvZbcDD81EOcT9EwnK2kJEQY/shWQGqOqSdEE37S QQNqLxL5Vk82og+pt9daCQmSkh5NC4pNwWdxXmCWsHfdR88PsXdx96L+ahrpfi0c7E J28Ni4rh8/VQaUJLENuWAO0+AB8ODk4BQ5oW87glYoegcsllmXVYnLasBYwPaS5AKE 2m8nsARtnCi8Q== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4dbDKw5H64z6tvZ; Tue, 23 Dec 2025 13:08:04 +0100 (CET) Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 23 Dec 2025 12:08:04 +0000 From: BP25 To: Andrei Borzenkov Cc: Roman Mamedov , Linux btrfs Subject: Re: Snapshots of individual files In-Reply-To: References: <79ae6c26545c107010719ee389947c1c@posteo.net> <20251223125647.6626b266@nvm> <1403c713e107106e18e000d7b0f81eaf@posteo.net> Message-ID: <282168f52d13e55e466c2fd079a246de@posteo.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Thanks for this message and the clarifications. The key was your note=20 that I can put the copy in the snapshots folder: is this correct? if yes=20 then Roman I think your answer indeed addresses my original question,=20 and I misspoke in my previous email, sorry. Is there a standard way to=20 'follow' the same file along its snapshotted versions? Say, ask btrfs to=20 return the list of snapshotted versions by giving input this or that=20 file in the current version of the filesystem? Note that if such file=20 was deleted and another with the same name created I don't want that new=20 file also to show up. And related question, is there any command that=20 would list the snapshotted files which have no corresponding in the=20 current version of the file system (for example because I deleted such=20 file after having snapshotted it)? Please CC or BCC me. Many thanks. On 23.12.2025 12:19, Andrei Borzenkov wrote: > On Tue, Dec 23, 2025 at 1:26=E2=80=AFPM BP25 wrote: >>=20 >> Dear Roman, >> Thanks for your informative answer. But this is precisely the wrong >> solution: btrfs snapshots shouldn't and in fact don't clutter the >> filesystem with previous versions of the files because such ghost >> versions materialise when the snapshot is mounted. >=20 > That depends on your subvolume layout. Nothing forces you to place the > file copy into the same directory as the source either. >> In my original >> message I seek for the analogous behaviour. >=20 > It is exactly analogous. >=20 >> Also I don't want to >> generate more and more copies... >>=20 >=20 > To reference a snapshot (be it subvolume or file) it must have a name > which you must provide. To create a snapshot with a given name in some > location this location must be accessible at the time the snapshot is > being created. As long as this location remains accessible its content > remains accessible. There is no difference between file and subvolume. >=20 > If you complain that you cannot mount a single file outside of the > default subvolume and can only mount subvolumes - it is an entirely > different question which is unrelated to how this file was created. Sure, I'm not asking about this now. >=20 >> On 23.12.2025 08:56, Roman Mamedov wrote: >> > On Tue, 23 Dec 2025 00:43:25 +0000 wrote: >> > >> >> Hello, >> >> Can any of you guys help me understand why it hasn't been made >> >> possible >> >> to snapshot individual files? Because technically it's trivial to >> >> implement therefore I suspect there must be some abstract reason... >> >> The >> >> only thing I can think of is the case where some file which was >> >> snapshotted is then deleted hence there is no way to 'select such >> >> file' >> >> and ask btrfs for the snapshotted versions... but even in this case I >> >> see no problem: either the convention is that when you delete a file >> >> then all snapshots of such individual file are also deleted, or bette= r >> >> there is a command that shows all files who have been deleted but hav= e >> >> have been snapshotted in the past. >> >> Any ideas? >> >> Please CC or BCC me cause I'm not subscribed. >> > >> > You can make "snapshots" of a file with: >> > >> > cp -a --reflink filename filename.snap >> > >> > from what I tested this appears to be atomic (entire file is reflinked >> > at >> > once), someone might correct me if I'm wrong. >> > >> > Works on modern XFS too. >>=20 >>=20