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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912c0e2b8bsm16226413f8f.64.2025.03.10.15.12.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Mar 2025 15:12:45 -0700 (PDT) Date: Mon, 10 Mar 2025 22:12:43 +0000 From: David Laight To: "Theodore Ts'o" Cc: "Artem S. Tashkinov" , linux-ext4@vger.kernel.org, Linux Kernel Mailing List Subject: Re: A syscall for changing birth time Message-ID: <20250310221243.0d5db7b3@pumpkin> In-Reply-To: <20250310135828.GB8837@mit.edu> References: <20250310135828.GB8837@mit.edu> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 10 Mar 2025 09:58:28 -0400 "Theodore Ts'o" wrote: > On Mon, Mar 10, 2025 at 07:26:00AM +0000, Artem S. Tashkinov wrote: > > > > Why is it that the Linux kernel supports reading btime, but there's no > > syscall to change it? At least for ext4 there's the debugfs utility, but > > for other filesystems there's just nothing. And even debugfs is not a > > solution, since it requires root privileges and an unmounted/mounted RO > > filesystem. > > POSIX and Single Unix Specification also doesn't provide a way to > allow userspace to set ctime (inode change time). That's because the > definition of "change time" is defined to include the time to change > anything about the inode metadata --- including the inode timestamps. > I'm sure that hadn't used to be the case. But as some point the 'ctime' changed from something that was usually the file create time (for some definition of create) to a pretty useless time that is almost a waste of disk space. David