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diff --git a/lib/libc/sys/open.2 b/lib/libc/sys/open.2
--- a/lib/libc/sys/open.2
+++ b/lib/libc/sys/open.2
@@ -28,7 +28,7 @@
.\" @(#)open.2 8.2 (Berkeley) 11/16/93
.\" $FreeBSD$
.\"
-.Dd February 23, 2021
+.Dd March 18, 2021
.Dt OPEN 2
.Os
.Sh NAME
@@ -168,6 +168,7 @@
O_CLOEXEC set FD_CLOEXEC upon open
O_VERIFY verify the contents of the file
O_RESOLVE_BENEATH path resolution must not cross the fd directory
+O_PATH record only the target path in the opened descriptor
.Ed
.Pp
Opening a file with
@@ -316,6 +317,35 @@
.Fn *at
family of functions.
.Pp
+.Dv O_PATH
+returns a file descriptor that can be used as directory file descriptor
+for
+.Xr openat 2
+and other calls takind a directory argument, like
+.Xr fstatat 2
+and others.
+The other functionality of the returned file descriptor is limited to
+the descriptor-level operations.
+It can be used for
+.Xr fcntl 2 ,
+.Xr dup 2 ,
+.Xr close 2 ,
+and for passing it using unix domain socket rights messages.
+Additionally,
+.Xr fstat 2
+works.
+But operations like
+.Xr read 2 ,
+.Xr ftruncate 2 ,
+and any other that operate on file and not on file descriptor (except
+.Xr fstat 2 ),
+are not allowed.
+See also the description of
+.Dv AT_EMPTY_PATH
+flag for
+.Xr fstatat 2
+and related syscalls.
+.Pp
If successful,
.Fn open
returns a non-negative integer, termed a file descriptor.
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -4960,6 +4960,42 @@
.fo_fill_kinfo = badfo_fill_kinfo,
};
+static int
+path_close(struct file *fp, struct thread *td)
+{
+ struct vnode *vp;
+ struct flock lf;
+
+ MPASS(fp->f_type == DTYPE_VNODE);
+
+ vp = fp->f_vnode;
+ fp->f_ops = &badfileops;
+ if ((fp->f_flag & FHASLOCK) != 0) {
+ lf.l_whence = SEEK_SET;
+ lf.l_start = 0;
+ lf.l_len = 0;
+ lf.l_type = F_UNLCK;
+ (void) VOP_ADVLOCK(vp, fp, F_UNLCK, &lf, F_FLOCK);
+ }
+ vrele(vp);
+ return (0);
+}
+
+struct fileops path_fileops = {
+ .fo_read = badfo_readwrite,
+ .fo_write = badfo_readwrite,
+ .fo_truncate = badfo_truncate,
+ .fo_ioctl = badfo_ioctl,
+ .fo_poll = badfo_poll,
+ .fo_kqfilter = badfo_kqfilter,
+ .fo_stat = vn_statfile,
+ .fo_close = path_close,
+ .fo_chmod = badfo_chmod,
+ .fo_chown = badfo_chown,
+ .fo_sendfile = badfo_sendfile,
+ .fo_fill_kinfo = vn_fill_kinfo,
+};
+
int
invfo_rdwr(struct file *fp, struct uio *uio, struct ucred *active_cred,
int flags, struct thread *td)
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -1174,14 +1174,16 @@
* files that switched type in the cdevsw fdopen() method.
*/
fp->f_vnode = vp;
+
/*
* If the file wasn't claimed by devfs bind it to the normal
* vnode operations here.
*/
if (fp->f_ops == &badfileops) {
- KASSERT(vp->v_type != VFIFO,
+ KASSERT(vp->v_type != VFIFO || (flags & O_PATH) != 0,
("Unexpected fifo fp %p vp %p", fp, vp));
- finit_vnode(fp, flags, NULL, &vnops);
+ finit_vnode(fp, flags, NULL, (flags & O_PATH) != 0 ?
+ &path_fileops : &vnops);
}
VOP_UNLOCK(vp);
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -102,7 +102,6 @@
static fo_ioctl_t vn_ioctl;
static fo_poll_t vn_poll;
static fo_kqfilter_t vn_kqfilter;
-static fo_stat_t vn_statfile;
static fo_close_t vn_closefile;
static fo_mmap_t vn_mmap;
static fo_fallocate_t vn_fallocate;
@@ -392,6 +391,12 @@
return (EOPNOTSUPP);
if (vp->v_type != VDIR && fmode & O_DIRECTORY)
return (ENOTDIR);
+
+ if ((fmode & O_PATH) != 0) {
+ error = vn_open_vnode_advlock(vp, fmode, fp);
+ return (error);
+ }
+
accmode = 0;
if (fmode & (FWRITE | O_TRUNC)) {
if (vp->v_type == VDIR)
@@ -1616,7 +1621,7 @@
/*
* File table vnode stat routine.
*/
-static int
+int
vn_statfile(struct file *fp, struct stat *sb, struct ucred *active_cred,
struct thread *td)
{
@@ -1775,7 +1780,7 @@
vp = fp->f_vnode;
fp->f_ops = &badfileops;
- ref= (fp->f_flag & FHASLOCK) != 0 && fp->f_type == DTYPE_VNODE;
+ ref = (fp->f_flag & FHASLOCK) != 0 && fp->f_type == DTYPE_VNODE;
error = vn_close1(vp, fp->f_flag, fp->f_cred, td, ref);
diff --git a/sys/sys/fcntl.h b/sys/sys/fcntl.h
--- a/sys/sys/fcntl.h
+++ b/sys/sys/fcntl.h
@@ -135,7 +135,7 @@
#if __BSD_VISIBLE
#define O_VERIFY 0x00200000 /* open only after verification */
-/* #define O_UNUSED1 0x00400000 */ /* Was O_BENEATH */
+#define O_PATH 0x00400000 /* fd is only a path */
#define O_RESOLVE_BENEATH 0x00800000 /* Do not allow name resolution to walk
out of cwd */
#endif
diff --git a/sys/sys/file.h b/sys/sys/file.h
--- a/sys/sys/file.h
+++ b/sys/sys/file.h
@@ -239,6 +239,7 @@
extern struct fileops vnops;
extern struct fileops badfileops;
+extern struct fileops path_fileops;
extern struct fileops socketops;
extern int maxfiles; /* kernel limit on number of open files */
extern int maxfilesperproc; /* per process limit on number of open files */
@@ -262,7 +263,7 @@
fo_chmod_t invfo_chmod;
fo_chown_t invfo_chown;
fo_sendfile_t invfo_sendfile;
-
+fo_stat_t vn_statfile;
fo_sendfile_t vn_sendfile;
fo_seek_t vn_seek;
fo_fill_kinfo_t vn_fill_kinfo;

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