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Tue, 25 Feb 2025 05:41:12 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 25 Feb 2025 11:40:51 +0100 From: "Arnd Bergmann" To: "Christian Brauner" Cc: "Amir Goldstein" , "Andrey Albershteyn" , "Darrick J. Wong" , "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" , "Jan Kara" , =?UTF-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , =?UTF-8?Q?G=C3=BCnther_Noack?= , 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 , linux-xfs@vger.kernel.org, =?UTF-8?Q?Pali_Roh=C3=A1r?= , "Theodore Ts'o" Message-Id: <3c860dc0-ba8d-4324-b286-c160b7d8d2c4@app.fastmail.com> In-Reply-To: <20250225-strom-kopflos-32062347cd13@brauner> References: <20250211-xattrat-syscall-v3-1-a07d15f898b2@kernel.org> <20250221181135.GW21808@frogsfrogsfrogs> <20250224-klinke-hochdekoriert-3f6be89005a8@brauner> <6b51ffa2-9d67-4466-865e-e703c1243352@app.fastmail.com> <20250225-strom-kopflos-32062347cd13@brauner> Subject: Re: [PATCH v3] fs: introduce getfsxattrat and setfsxattrat syscalls Content-Type: text/plain Content-Transfer-Encoding: 7bit On Tue, Feb 25, 2025, at 11:22, Christian Brauner wrote: > On Tue, Feb 25, 2025 at 09:02:04AM +0100, Arnd Bergmann wrote: >> On Mon, Feb 24, 2025, at 12:32, Christian Brauner wrote: >> >> The ioctl interface relies on the existing behavior, see >> 0a6eab8bd4e0 ("vfs: support FS_XFLAG_COWEXTSIZE and get/set of >> CoW extent size hint") for how it was previously extended >> with an optional flag/word. I think that is fine for the syscall >> as well, but should be properly documented since it is different >> from how most syscalls work. > > If we're doing a new system call I see no reason to limit us to a > pre-existing structure or structure layout. Obviously we could create a new structure, but I also see no reason to do so. The existing ioctl interface was added in in 2002 as part of linux-2.5.35 with 16 bytes of padding, half of which have been used so far. If this structure works for another 23 years before we run out of spare bytes, I think that's good enough. Building in an incompatible way to handle potential future contents would just make it harder to use for any userspace that wants to use the new syscalls but still needs a fallback to the ioctl version. Arnd