[PATCH 28/32] nsfs: support exhaustive file handles
From: Christian Brauner <brauner@kernel.org>
Date: 2025-09-10 14:39:53
Also in:
cgroups, linux-block, linux-fsdevel, linux-kselftest, linux-nfs, lkml
Subsystem:
file locking (flock() and fcntl()/lockf()), filesystems (vfs and infrastructure), filesystems [exportfs], the rest · Maintainers:
Jeff Layton, Chuck Lever, Alexander Viro, Christian Brauner, Linus Torvalds
Pidfd file handles are exhaustive meaning they don't require a handle on another pidfd to pass to open_by_handle_at() so it can derive the filesystem to decode in. Instead it can be derived from the file handle itself. The same is possible for namespace file handles. Signed-off-by: Christian Brauner <brauner@kernel.org> --- fs/fhandle.c | 6 ++++++ fs/internal.h | 1 + fs/nsfs.c | 10 ++++++++++ include/uapi/linux/fcntl.h | 1 + 4 files changed, 18 insertions(+)
diff --git a/fs/fhandle.c b/fs/fhandle.c
index 7c236f64cdea..f18c855bb0c2 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c@@ -11,6 +11,7 @@ #include <linux/personality.h> #include <linux/uaccess.h> #include <linux/compat.h> +#include <linux/nsfs.h> #include "internal.h" #include "mount.h"
@@ -189,6 +190,11 @@ static int get_path_anchor(int fd, struct path *root) return 0; } + if (fd == FD_NSFS_ROOT) { + nsfs_get_root(root); + return 0; + } + return -EBADF; }
diff --git a/fs/internal.h b/fs/internal.h
index 38e8aab27bbd..a33d18ee5b74 100644
--- a/fs/internal.h
+++ b/fs/internal.h@@ -355,3 +355,4 @@ int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path, int anon_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry, struct iattr *attr); void pidfs_get_root(struct path *path); +void nsfs_get_root(struct path *path);
diff --git a/fs/nsfs.c b/fs/nsfs.c
index a1585a2f4f03..3c6fcf652633 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c@@ -25,6 +25,14 @@ static struct vfsmount *nsfs_mnt; +static struct path nsfs_root_path = {}; + +void nsfs_get_root(struct path *path) +{ + *path = nsfs_root_path; + path_get(path); +} + static long ns_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg); static const struct file_operations ns_file_operations = {
@@ -616,4 +624,6 @@ void __init nsfs_init(void) if (IS_ERR(nsfs_mnt)) panic("can't set nsfs up\n"); nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER; + nsfs_root_path.mnt = nsfs_mnt; + nsfs_root_path.dentry = nsfs_mnt->mnt_root; }
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index f291ab4f94eb..3741ea1b73d8 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h@@ -111,6 +111,7 @@ #define PIDFD_SELF_THREAD_GROUP -10001 /* Current thread group leader. */ #define FD_PIDFS_ROOT -10002 /* Root of the pidfs filesystem */ +#define FD_NSFS_ROOT -10003 /* Root of the nsfs filesystem */ #define FD_INVALID -10009 /* Invalid file descriptor: -10000 - EBADF = -10009 */ /* Generic flags for the *at(2) family of syscalls. */
--
2.47.3