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[2003:dc:6f46:c100:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b8a285c2sm174555925e9.32.2025.05.06.09.40.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 May 2025 09:40:18 -0700 (PDT) From: Max Kellermann To: gregkh@linuxfoundation.org, tj@kernel.org, linux-kernel@vger.kernel.org Cc: Max Kellermann Subject: [PATCH] fs/kernfs: implement STATX_BTIME Date: Tue, 6 May 2025 18:40:17 +0200 Message-ID: <20250506164017.249149-1-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This allows finding out when an inode was initially created, for example: - when was a device plugged in (and its node in sysfs was created)? - when was a cgroup created? kernfs currently only implements `atime`, `mtime` and `ctime`. All of these are volatile (`mtime` and `ctime` get updated automatically, and `atime` can be mainpulated using utime()). Therefore, I suggest implementing STATX_BTIME to have a reliable birth time in userspace. Signed-off-by: Max Kellermann --- fs/kernfs/dir.c | 2 ++ fs/kernfs/inode.c | 6 ++++++ include/linux/kernfs.h | 7 +++++++ 3 files changed, 15 insertions(+) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index fc70d72c3fe8..9a6857f2f3d7 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -678,6 +678,8 @@ static struct kernfs_node *__kernfs_new_node(struct ker= nfs_root *root, goto err_out3; } =20 + ktime_get_real_ts64(&kn->btime); + return kn; =20 err_out3: diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c index b83054da68b3..1ff2ee62bfe6 100644 --- a/fs/kernfs/inode.c +++ b/fs/kernfs/inode.c @@ -189,6 +189,12 @@ int kernfs_iop_getattr(struct mnt_idmap *idmap, struct kernfs_root *root =3D kernfs_root(kn); =20 down_read(&root->kernfs_iattr_rwsem); + + if (request_mask & STATX_BTIME) { + stat->result_mask |=3D STATX_BTIME; + stat->btime =3D kn->btime; + } + kernfs_refresh_inode(kn, inode); generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat); up_read(&root->kernfs_iattr_rwsem); diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index b5a5f32fdfd1..9332aadf4b48 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -229,6 +229,13 @@ struct kernfs_node { void *priv; struct kernfs_iattrs *iattr; =20 + /* + * The birth time (for STATX_BTIME). It lives here and not in + * struct kernfs_iattrs because the latter is only created on + * demand, not at actual node birth time. + */ + struct timespec64 btime; + struct rcu_head rcu; }; =20 --=20 2.47.2