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Hallyn" , Martin KaFai Lau , Eduard Zingerman , Yonghong Song , John Fastabend , Kumar Kartikeya Dwivedi , Jiri Olsa , Jeff Layton , Amir Goldstein , Mateusz Guzik , Shuah Khan , Tingmao Wang , Justin Suess Subject: [RFC PATCH bpf-next 05/12] namei: make vfs_walk_ancestors() stepwise Date: Mon, 5 Oct 2026 20:20:12 -0400 Message-ID: <20261006002020.2890858-6-utilityemal77@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261006002020.2890858-1-utilityemal77@gmail.com> References: <20261006002020.2890858-1-utilityemal77@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Restructure the walk into a stepwise engine - vfs_walk_start(), vfs_walk_next(), vfs_walk_end() - private to fs/, so an iterating consumer (BPF) can drive it with every step and invariant staying in namei.c. vfs_walk_ancestors() becomes a loop over it, preserving the callback contract. The position's flags move into the walk state, where the next step needs them anyway: stepping off a disconnected position resumes at the root of its mount. Signed-off-by: Justin Suess --- fs/internal.h | 15 ++++++ fs/namei.c | 141 ++++++++++++++++++++++++++++++++++++-------------- 2 files changed, 117 insertions(+), 39 deletions(-) diff --git a/fs/internal.h b/fs/internal.h index c658c8a5ebd5..3ce2220ff57f 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -71,6 +71,21 @@ struct dentry *start_dirop(struct dentry *parent, struct qstr *name, unsigned int lookup_flags); int lookup_noperm_common(struct qstr *qname, struct dentry *base); +/* + * The stepwise engine under vfs_walk_ancestors(); fs-internal so iterating + * consumers (BPF) can drive it, with the walk invariants staying in namei.c. + */ +struct vfs_ancestor_walk { + struct path pos; + unsigned int pos_flags; /* VFS_WALK_POS_* describing pos */ + unsigned int flags; /* VFS_WALK_* */ +}; + +void vfs_walk_start(struct vfs_ancestor_walk *aw, const struct path *path, + unsigned int flags); +int vfs_walk_next(struct vfs_ancestor_walk *aw); +void vfs_walk_end(struct vfs_ancestor_walk *aw); + void __init filename_init(void); /* diff --git a/fs/namei.c b/fs/namei.c index 2e6ea19714b2..73f25152d917 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2229,6 +2229,97 @@ static struct dentry *__path_walk_parent(struct path *path, const struct path *r return dget(path->dentry); } +static unsigned int vfs_walk_pos_flags(const struct vfsmount *mnt, + const struct dentry *dentry) +{ + if (unlikely(IS_ROOT(dentry) && dentry != mnt->mnt_root)) + return VFS_WALK_POS_DISCONNECTED; + return 0; +} + +/* No boundary: ancestor walks go up to the real root. */ +static const struct path vfs_walk_no_root; + +/* Internal walk flag: the starting position has been yielded. */ +#define VFS_WALK_STARTED BIT(31) + +/** + * vfs_walk_start - begin a stepwise ancestor walk + * @aw: walk state, valid until vfs_walk_end() + * @path: position to walk up from; never modified + * @flags: %VFS_WALK_* flags; none defined yet, pass 0 + */ +void vfs_walk_start(struct vfs_ancestor_walk *aw, const struct path *path, + unsigned int flags) +{ + aw->pos = *path; + aw->flags = flags; + aw->pos_flags = 0; + path_get(&aw->pos); +} + +static int vfs_walk_step_ref(struct vfs_ancestor_walk *aw) +{ + struct dentry *parent; + + if (unlikely(aw->pos_flags & VFS_WALK_POS_DISCONNECTED)) { + /* Resume at the root of the disconnected position's mount. */ + dput(aw->pos.dentry); + aw->pos.dentry = dget(aw->pos.mnt->mnt_root); + aw->pos_flags = 0; + return 0; + } + parent = __path_walk_parent(&aw->pos, &vfs_walk_no_root, + LOOKUP_BENEATH); + if (IS_ERR(parent)) + /* The real root. */ + return 1; + /* + * A mount crossing can step onto a disconnected root, whose parent + * is itself: only then is the mountpoint itself yielded, flagged. + */ + aw->pos_flags = parent == aw->pos.dentry ? + VFS_WALK_POS_DISCONNECTED | VFS_WALK_POS_MOUNTPOINT : + vfs_walk_pos_flags(aw->pos.mnt, parent); + dput(aw->pos.dentry); + aw->pos.dentry = parent; + return 0; +} + +/** + * vfs_walk_next - yield the walk's next position in @aw->pos + * @aw: the walk + * + * The first call yields the starting position itself. @aw->pos_flags + * carries the position's %VFS_WALK_POS_* flags, with the semantics + * described at vfs_walk_ancestors(). + * + * Returns: 0 with @aw->pos valid, 1 once the walk has passed the real + * root. + */ +int vfs_walk_next(struct vfs_ancestor_walk *aw) +{ + if (aw->flags & VFS_WALK_STARTED) { + int err = vfs_walk_step_ref(aw); + + if (err) + return err; + } else { + aw->flags |= VFS_WALK_STARTED; + aw->pos_flags = vfs_walk_pos_flags(aw->pos.mnt, aw->pos.dentry); + } + return 0; +} + +/** + * vfs_walk_end - finish a stepwise ancestor walk + * @aw: the walk; its positions, including @aw->pos, become invalid + */ +void vfs_walk_end(struct vfs_ancestor_walk *aw) +{ + path_put(&aw->pos); +} + /** * vfs_walk_ancestors - invoke a callback on a path and each of its ancestors * @path: path to walk up from; the caller's path is never modified @@ -2253,55 +2344,27 @@ int vfs_walk_ancestors(const struct path *path, unsigned int pos_flags, void *data), void *data, unsigned int flags) { - const struct path root = {}; - struct path walk = *path; - unsigned int pos_flags = 0; + struct vfs_ancestor_walk aw; int ret; - path_get(&walk); - if (unlikely(IS_ROOT(walk.dentry) && - walk.dentry != walk.mnt->mnt_root)) - pos_flags = VFS_WALK_POS_DISCONNECTED; + vfs_walk_start(&aw, path, flags); for (;;) { - struct dentry *parent; - - ret = cb(&walk, pos_flags, data); + ret = vfs_walk_next(&aw); + if (ret) { + if (ret == 1) + /* The real root was reached. */ + ret = 0; + break; + } + ret = cb(&aw.pos, aw.pos_flags, data); if (ret < 0) break; if (ret == VFS_WALK_STOP) { ret = 1; break; } - - if (unlikely(pos_flags & VFS_WALK_POS_DISCONNECTED)) { - dput(walk.dentry); - walk.dentry = dget(walk.mnt->mnt_root); - pos_flags = 0; - continue; - } - parent = __path_walk_parent(&walk, &root, LOOKUP_BENEATH); - if (IS_ERR(parent)) { - /* The real root. */ - ret = 0; - break; - } - /* - * A mount crossing can step onto a disconnected root, whose - * parent is itself: only then is the mountpoint itself - * visited, flagged, next iteration. - */ - if (unlikely(parent == walk.dentry)) - pos_flags = VFS_WALK_POS_DISCONNECTED | - VFS_WALK_POS_MOUNTPOINT; - else if (unlikely(IS_ROOT(parent) && - parent != walk.mnt->mnt_root)) - pos_flags = VFS_WALK_POS_DISCONNECTED; - else - pos_flags = 0; - dput(walk.dentry); - walk.dentry = parent; } - path_put(&walk); + vfs_walk_end(&aw); return ret; } -- 2.55.0