Re: [pseudo] [PATCH v3 1/6] ports/linux/guts: Add open_tree wrapper

[Paul Barker <paul@pbarker.dev>]

On Mon, 2026-09-07 at 14:18 +0300, frezidok1@gmail.com wrote:
> From: Dmitry Sakhonchik <frezidok1@gmail.com>
> 
> [YOCTO #16379]
> 
> OPEN_TREE_CLONE is not handled since it requires CAP_SYS_ADMIN and is outside the common pseudo use case.

We should at least log an error if OPEN_TREE_CLONE is seen instead of
silently ignoring it.

> 
> Signed-off-by: Dmitry Sakhonchik <frezidok1@gmail.com>
> ---
>  ports/linux/guts/open_tree.c | 46 ++++++++++++++++++++++++++++++++++++
>  ports/linux/portdefs.h       |  9 +++++++
>  ports/linux/wrapfuncs.in     |  1 +
>  3 files changed, 56 insertions(+)
>  create mode 100644 ports/linux/guts/open_tree.c
> 
> diff --git a/ports/linux/guts/open_tree.c b/ports/linux/guts/open_tree.c
> new file mode 100644
> index 0000000..6c2aad9
> --- /dev/null
> +++ b/ports/linux/guts/open_tree.c
> @@ -0,0 +1,46 @@
> +/*
> + * Copyright (c) 2026 Yocto Project
> + * guts/COPYRIGHT for information.
> + *
> + * SPDX-License-Identifier: LGPL-2.1-only
> + *
> + * int open_tree(int dirfd, const char *path, unsigned int flags)
> + *	int rc = -1;
> + */
> +
> +	struct stat64 buf;
> +	int save_errno;
> +	char *pseudo_path;
> +
> +	if (real_open_tree) {
> +		pseudo_debug(PDBGF_SYSCALL, "open_tree, calling open_tree.\n");
> +		rc = real_open_tree(dirfd, path, flags);
> +	} else {
> +		pseudo_debug(PDBGF_SYSCALL, "open_tree, calling syscall.\n");
> +		rc = real_syscall(SYS_open_tree, dirfd, path, flags);
> +	}

The commit message or a comment should briefly explain why we need to
handle both ways of invoking the real open_tree syscall.

> +
> +	pseudo_path = pseudo_root_path(__func__, __LINE__, dirfd, path, 0);

This should be after the (rc != -1) conditional, as this call could
clobber errno.

> +
> +	if (rc != -1) {

Nitpick: To save indentation, we can check for (rc == -1) and return early.

> +		save_errno = errno;
> +		int stat_rc;
> +
> +		stat_rc = real___fxstatat64(_STAT_VER, dirfd, pseudo_path, &buf, (flags & AT_SYMLINK_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0);
> +
> +		pseudo_debug(PDBGF_FILE, "open_tree(path %s), flags %o, stat rc %d, stat mode %o\n",
> +			pseudo_path, flags, stat_rc, buf.st_mode);
> +
> +		if (stat_rc != -1) {
> +			pseudo_client_op(OP_OPEN, 0, rc, dirfd, pseudo_path, &buf);
> +		} else {
> +			pseudo_debug(PDBGF_FILE, "open_tree(fd %d, path %d/%s, flags %d) succeeded, but stat failed (%s).\n",
> +				rc, dirfd, pseudo_path, flags, strerror(errno));
> +			pseudo_client_op(OP_OPEN, 0, rc, dirfd, pseudo_path, 0);
> +		}
> +		errno = save_errno;
> +	}
> +
> +/*	return rc;
> + * }
> + */
> diff --git a/ports/linux/portdefs.h b/ports/linux/portdefs.h
> index 1f1a41a..565fed9 100644
> --- a/ports/linux/portdefs.h
> +++ b/ports/linux/portdefs.h
> @@ -82,3 +82,12 @@ extern int unshare(int flags);
>  
>  #define SYS_openat2 __NR_openat2
>  #endif
> +
> +#ifndef SYS_open_tree
> +
> +#ifndef __NR_open_tree
> +#define __NR_open_tree 428
> +#endif
> +
> +#define SYS_open_tree __NR_open_tree
> +#endif
> diff --git a/ports/linux/wrapfuncs.in b/ports/linux/wrapfuncs.in
> index 3cea20a..a51e9a0 100644
> --- a/ports/linux/wrapfuncs.in
> +++ b/ports/linux/wrapfuncs.in
> @@ -10,6 +10,7 @@ int lchown(const char *path, uid_t owner, gid_t group); /* flags=AT_SYMLINK_NOFO
>  int __fxstatat(int ver, int dirfd, const char *path, struct stat *buf, int flags);
>  int openat(int dirfd, const char *path, int flags, ...{mode_t mode}); /* flags=((flags&O_NOFOLLOW)||((flags&(O_CREAT|O_EXCL))==(O_CREAT|O_EXCL))), noignore_path=1 */
>  int __openat_2(int dirfd, const char *path, int flags); /* flags=((flags&O_NOFOLLOW)||((flags&(O_CREAT|O_EXCL))==(O_CREAT|O_EXCL))), noignore_path=1 */
> +int open_tree(int dirfd, const char *path, unsigned int flags); /* noignore_path=1 */

Does this need preserve_paths=1 (similar to openat2())?

That would require us to account for a possible chroot in the
open_tree() guts, but it would avoid us running pseudo_root_path() on an
already canonicalized path which may introduce problems under a chroot.

>  int mknod(const char *path, mode_t mode, dev_t dev); /* real_func=pseudo_mknod */
>  int mknodat(int dirfd, const char *path, mode_t mode, dev_t dev); /* real_func=pseudo_mknodat */
>  int __xmknod(int ver, const char *path, mode_t mode, dev_t *dev); /* flags=AT_SYMLINK_NOFOLLOW */
> 

-- 
Paul Barker