From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4BAB01C5D44; Thu, 27 Mar 2025 21:13:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743109997; cv=none; b=c2KdwSLXP9K3+OHn/USovQkhSLEy8Nm49StS2iFwje2rLqjC3BHjkAbnuA9qkE+hKOQDFs4cSAK7zLqlpA8d3aSgL+pFV0AGst5XELQ5aRGckmtXMrE+EAbgxHgjfTA9W1cCsDPyxUR00rPMSCkfr9AAb/7gnMEMUZAIMWdUCzU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743109997; c=relaxed/simple; bh=UMe20iZUuagLPcGXISw0+QA+ECxOrxToOggTG9tCl7c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=oNOTV/cT/GY2aJ5Kjyacm2I8GB1Hly37RK6gSkMEcS+Cxtpdj7YJJjJG2y9jJ41pnea4cp5NNRTQAs4zBbd0DLDlLLIYNgNrKSuc8J5ynMPmJOvAORPtFq5uKF1XpqqSn5GVKOzS4oM5Y0VtZOL8An+pBG6tqVGYeV5xNbPCvvA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pjEZiBD8; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pjEZiBD8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7A25C4CEDD; Thu, 27 Mar 2025 21:13:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743109997; bh=UMe20iZUuagLPcGXISw0+QA+ECxOrxToOggTG9tCl7c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pjEZiBD8e0ystDPIxq5rYB0BhzyFxROf/Ryj0zF5OUcIL6U1NSR+ohFVoWx75A5O1 zUDoz9NmZeNhN/ml8TDozSK+FHArIgNzTxMJisrUKKp0QrJDSE/48Gm/7w9gYMhpsC 0cjmF7vuhAtNHlUTYpDxoSTAP2NIVeQICKV+KIimhR/fvFSexTVvShIeniU2H9xu1t lHLCiQ6glh0GSWZ9t6y1BCD9rlFIlXjQRsKBMmV5eyX9HujEsmEI+WN4RIPfT1OqXc wkwp1dgNkF3j8gBSpRl+CYes246BZH+3WMNbFuFYx4I5178EjPlyXmTihrByrFKRp0 bGdzAIry8bGnQ== Received: by pali.im (Postfix) id 9561981B; Thu, 27 Mar 2025 22:13:01 +0100 (CET) Date: Thu, 27 Mar 2025 22:13:01 +0100 From: Pali =?utf-8?B?Um9ow6Fy?= To: Amir Goldstein Cc: Andrey Albershteyn , Richard Henderson , Matt Turner , Russell King , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Michal Simek , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Andreas Larsson , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Chris Zankel , Max Filippov , Alexander Viro , Christian Brauner , Jan Kara , =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , =?utf-8?Q?G=C3=BCnther?= Noack , Arnd Bergmann , Paul Moore , James Morris , "Serge E. Hallyn" , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, selinux@vger.kernel.org, Andrey Albershteyn , linux-xfs@vger.kernel.org Subject: Re: [PATCH v4 0/3] fs: introduce getfsxattrat and setfsxattrat syscalls Message-ID: <20250327211301.kdsohqou3s242coa@pali> References: <20250321-xattrat-syscall-v4-0-3e82e6fb3264@kernel.org> <20250323103234.2mwhpsbigpwtiby4@pali> <20250327192629.ivnarhlkfbhbzjcl@pali> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180716 On Thursday 27 March 2025 21:57:34 Amir Goldstein wrote: > On Thu, Mar 27, 2025 at 8:26 PM Pali Rohár wrote: > > > > On Thursday 27 March 2025 12:47:02 Amir Goldstein wrote: > > > On Sun, Mar 23, 2025 at 11:32 AM Pali Rohár wrote: > > > > > > > > On Sunday 23 March 2025 09:45:06 Amir Goldstein wrote: > > > > > On Fri, Mar 21, 2025 at 8:50 PM Andrey Albershteyn wrote: > > > > > > > > > > > > This patchset introduced two new syscalls getfsxattrat() and > > > > > > setfsxattrat(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl() > > > > > > except they use *at() semantics. Therefore, there's no need to open the > > > > > > file to get an fd. > > > > > > > > > > > > These syscalls allow userspace to set filesystem inode attributes on > > > > > > special files. One of the usage examples is XFS quota projects. > > > > > > > > > > > > XFS has project quotas which could be attached to a directory. All > > > > > > new inodes in these directories inherit project ID set on parent > > > > > > directory. > > > > > > > > > > > > The project is created from userspace by opening and calling > > > > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special > > > > > > files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left > > > > > > with empty project ID. Those inodes then are not shown in the quota > > > > > > accounting but still exist in the directory. This is not critical but in > > > > > > the case when special files are created in the directory with already > > > > > > existing project quota, these new inodes inherit extended attributes. > > > > > > This creates a mix of special files with and without attributes. > > > > > > Moreover, special files with attributes don't have a possibility to > > > > > > become clear or change the attributes. This, in turn, prevents userspace > > > > > > from re-creating quota project on these existing files. > > > > > > > > > > > > Christian, if this get in some mergeable state, please don't merge it > > > > > > yet. Amir suggested these syscalls better to use updated struct fsxattr > > > > > > with masking from Pali Rohár patchset, so, let's see how it goes. > > > > > > > > > > Andrey, > > > > > > > > > > To be honest I don't think it would be fair to delay your syscalls more > > > > > than needed. > > > > > > > > I agree. > > > > > > > > > If Pali can follow through and post patches on top of your syscalls for > > > > > next merge window that would be great, but otherwise, I think the > > > > > minimum requirement is that the syscalls return EINVAL if fsx_pad > > > > > is not zero. we can take it from there later. > > > > > > > > IMHO SYS_getfsxattrat is fine in this form. > > > > > > > > For SYS_setfsxattrat I think there are needed some modifications > > > > otherwise we would have problem again with backward compatibility as > > > > is with ioctl if the syscall wants to be extended in future. > > > > > > > > I would suggest for following modifications for SYS_setfsxattrat: > > > > > > > > - return EINVAL if fsx_xflags contains some reserved or unsupported flag > > > > > > > > - add some flag to completely ignore fsx_extsize, fsx_projid, and > > > > fsx_cowextsize fields, so SYS_setfsxattrat could be used just to > > > > change fsx_xflags, and so could be used without the preceding > > > > SYS_getfsxattrat call. > > > > > > > > What do you think about it? > > > > > > I think all Andrey needs to do now is return -EINVAL if fsx_pad is not zero. > > > > > > You can use this later to extend for the semantics of flags/fields mask > > > and we can have a long discussion later on what this semantics should be. > > > > > > Right? > > > > > > Amir. > > > > It is really enough? > > I don't know. Let's see... > > > All new extensions later would have to be added > > into fsx_pad fields, and currently unused bits in fsx_xflags would be > > unusable for extensions. > > I am working under the assumption that the first extension would be > to support fsx_xflags_mask and from there, you could add filesystem > flags support checks and then new flags. Am I wrong? > > Obviously, fsx_xflags_mask would be taken from fsx_pad space. > After that extension is implemented, calling SYS_setfsxattrat() with > a zero fsx_xflags_mask would be silly for programs that do not do > the legacy get+set. > > So when we introduce fsx_xflags_mask, we could say that a value > of zero means that the mask is not being checked at all and unknown > flags in set syscall are ignored (a.k.a legacy ioctl behavior). > > Programs that actually want to try and set without get will have to set > a non zero fsx_xflags_mask to do something useful. Here we need to also solve the problem that without GET call we do not have valid values for fsx_extsize, fsx_projid, and fsx_cowextsize. So maybe we would need some flag in fsx_pad that fsx_extsize, fsx_projid, or fsx_cowextsize are ignored/masked. > I don't think this is great. > I would rather that the first version of syscalls will require the mask > and will always enforce filesystems supported flags. It is not great... But what about this? In a first step (part of this syscall patch series) would be just a check that fsx_pad is zero. Non-zero will return -EINVAL. In next changes would added fsx_filter bit field, which for each fsx_xflags and also for fsx_extsize, fsx_projid, and fsx_cowextsize fields would add a new bit flag which would say (when SET) that the particular thing has to be ignored. So when fsx_pad is all-zeros then fsx_filter (first field in fsx_pad) would say that nothing in fsx_xflags, fsx_extsize, fsx_projid, and fsx_cowextsize is ignored, and hence behave like before. And when something in fsx_pad/fsx_filter is set then it says which fields are ignored/filtered-out. > If you can get those patches (on top of current series) posted and > reviewed in time for the next merge window, including consensus > on the actual semantics, that would be the best IMO. I think that this starting to be more complicated to rebase my patches in a way that they do not affect IOCTL path but implement it properly for new syscall path. It does not sounds like a trivial thing which I would finish in merge window time and having proper review and consensus on this. > But I am just preparing a plan B in case you do not have time to > work on the patches or if consensus on the API extensions is not > reached on time. > > I think that for plan B, the minimum is to verify zero pad field and > that is something that this syscall has to do anyway, because this > is the way that backward compact APIs work. > > If you want the syscall to always return -EINVAL for setting xflags > that are currently undefined I agree that would be nice as well. > > Thanks, > Amir.