fs: implement openat and friends

The EFI file system API takes as handle an arbitrary file within the
volume. Directory iteration should happen relative to that file, which
lends itself well to mapping this to openat and friends.

Add support for these to barebox in preparation.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20240304190038.3486881-36-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 80 insertions, 60 deletions

diff --git a/fs/fs.c b/fs/fs.c
index bf527f1b2d..6b71440318 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -130,10 +130,11 @@ void cdev_print(const struct cdev *cdev)
 }
 EXPORT_SYMBOL(cdev_print);
 
-static struct fs_device *get_fsdevice_by_path(const char *path);
+static struct fs_device *get_fsdevice_by_path(int dirfd, const char *path);
 
 void stat_print(const char *filename, const struct stat *st)
 {
+	int dirfd = AT_FDCWD;
 	struct block_device *bdev = NULL;
 	struct fs_device *fdev;
 	struct cdev *cdev = NULL;
@@ -156,7 +157,7 @@ void stat_print(const char *filename, const struct stat *st)
 	if (st->st_mode & S_IFCHR) {
 		char *path;
 
-		path = canonicalize_path(filename);
+		path = canonicalize_path(dirfd, filename);
 		if (path) {
 			const char *devicefile = devpath_to_name(path);
 			struct cdev *lcdev;
@@ -198,7 +199,7 @@ void stat_print(const char *filename, const struct stat *st)
 	if (type)
 		printf("  %s%s", typeprefix, type);
 
-	fdev = get_fsdevice_by_path(filename);
+	fdev = get_fsdevice_by_path(dirfd, filename);
 
 	printf("\nDevice: %s\tInode: %lu\n",
 	       fdev ? dev_name(&fdev->dev) : "<unknown>",
@@ -235,7 +236,7 @@ postcore_initcall(init_fs);
 
 struct filename;
 
-static int filename_lookup(struct filename *name, unsigned flags,
+static int filename_lookup(int dirfd, struct filename *name, unsigned flags,
 			   struct path *path);;
 static struct filename *getname(const char *filename);
 static void path_put(const struct path *path);
@@ -282,7 +283,7 @@ struct cdev *get_cdev_by_mountpath(const char *path)
 {
 	struct fs_device *fsdev;
 
-	fsdev = get_fsdevice_by_path(path);
+	fsdev = get_fsdevice_by_path(AT_FDCWD, path);
 	if (!fsdev)
 		return NULL;
 
@@ -293,7 +294,7 @@ char *get_mounted_path(const char *path)
 {
 	struct fs_device *fdev;
 
-	fdev = get_fsdevice_by_path(path);
+	fdev = get_fsdevice_by_path(AT_FDCWD, path);
 	if (!fdev)
 		return NULL;
 
@@ -828,7 +829,7 @@ static void fs_remove(struct device *dev)
 	if (fsdev->loop && fsdev->cdev) {
 		cdev_remove_loop(fsdev->cdev);
 
-		ret = filename_lookup(getname(fsdev->backingstore),
+		ret = filename_lookup(AT_FDCWD, getname(fsdev->backingstore),
 				      LOOKUP_FOLLOW, &path);
 		if (!ret) {
 			mntput(path.mnt);
@@ -912,7 +913,7 @@ int fsdev_open_cdev(struct fs_device *fsdev)
 	parseopt_b(fsdev->options, "loop", &fsdev->loop);
 	parseopt_llu_suffix(fsdev->options, "offset", &offset);
 	if (fsdev->loop) {
-		ret = filename_lookup(getname(fsdev->backingstore),
+		ret = filename_lookup(AT_FDCWD, getname(fsdev->backingstore),
 				      LOOKUP_FOLLOW, &path);
 		if (ret)
 			return ret;
@@ -1194,7 +1195,7 @@ char *path_get_linux_rootarg(const char *path)
 	struct fs_device *fsdev;
 	const char *str;
 
-	fsdev = get_fsdevice_by_path(path);
+	fsdev = get_fsdevice_by_path(AT_FDCWD, path);
 	if (!fsdev)
 		return ERR_PTR(-EINVAL);
 
@@ -1217,7 +1218,7 @@ bool __is_tftp_fs(const char *path)
 {
 	struct fs_device *fsdev;
 
-	fsdev = get_fsdevice_by_path(path);
+	fsdev = get_fsdevice_by_path(AT_FDCWD, path);
 	if (!fsdev)
 		return false;
 
@@ -2156,9 +2157,10 @@ OK:
 	}
 }
 
-static const char *path_init(struct nameidata *nd, unsigned flags)
+static const char *path_init(int dirfd, struct nameidata *nd, unsigned flags)
 {
 	const char *s = nd->name->name;
+	FILE *f = NULL;
 
 	nd->last_type = LAST_ROOT; /* if there are only slashes... */
 	nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
@@ -2167,12 +2169,23 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
 	nd->path.mnt = NULL;
 	nd->path.dentry = NULL;
 
+	/* We don't check for error here yet, as POSIX allows checking
+	 * whether paths are absolute with openat(-1, path, O_PATH)
+	 */
+	if (dirfd != AT_FDCWD)
+		f = fd_to_file(dirfd);
+
 	if (*s == '/') {
 		get_root(&nd->path);
-		return s;
-	} else {
+	} else if (dirfd == AT_FDCWD) {
 		get_pwd(&nd->path);
-		return s;
+	} else {
+		if (IS_ERR(f))
+			return ERR_CAST(f);
+
+		nd->path.mnt = &f->fsdev->vfsmount;
+		nd->path.dentry = f->dentry;
+		follow_mount(&nd->path);
 	}
 
 	return s;
@@ -2210,10 +2223,10 @@ static void terminate_walk(struct nameidata *nd)
 }
 
 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
-static int path_parentat(struct nameidata *nd, unsigned flags,
+static int path_parentat(int dirfd, struct nameidata *nd, unsigned flags,
 				struct path *parent)
 {
-	const char *s = path_init(nd, flags);
+	const char *s = path_init(dirfd, nd, flags);
 	int err;
 
 	if (IS_ERR(s))
@@ -2229,7 +2242,8 @@ static int path_parentat(struct nameidata *nd, unsigned flags,
 	return err;
 }
 
-static struct filename *filename_parentat(struct filename *name,
+static struct filename *filename_parentat(int dirfd,
+				struct filename *name,
 				unsigned int flags, struct path *parent,
 				struct qstr *last, int *type)
 {
@@ -2241,7 +2255,7 @@ static struct filename *filename_parentat(struct filename *name,
 
 	set_nameidata(&nd, name);
 
-	retval = path_parentat(&nd, flags, parent);
+	retval = path_parentat(dirfd, &nd, flags, parent);
 	if (likely(!retval)) {
 		*last = nd.last;
 		*type = nd.last_type;
@@ -2253,7 +2267,7 @@ static struct filename *filename_parentat(struct filename *name,
 	return name;
 }
 
-static struct dentry *filename_create(struct filename *name,
+static struct dentry *filename_create(int dirfd, struct filename *name,
 				struct path *path, unsigned int lookup_flags)
 {
 	struct dentry *dentry = ERR_PTR(-EEXIST);
@@ -2262,7 +2276,7 @@ static struct dentry *filename_create(struct filename *name,
 	int error;
 	bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
 
-	name = filename_parentat(name, 0, path, &last, &type);
+	name = filename_parentat(dirfd, name, 0, path, &last, &type);
 	if (IS_ERR(name))
 		return ERR_CAST(name);
 
@@ -2306,7 +2320,7 @@ out:
 	return dentry;
 }
 
-static int filename_lookup(struct filename *name, unsigned flags,
+static int filename_lookup(int dirfd, struct filename *name, unsigned flags,
 			   struct path *path)
 {
 	int err;
@@ -2318,7 +2332,7 @@ static int filename_lookup(struct filename *name, unsigned flags,
 
 	set_nameidata(&nd, name);
 
-	s = path_init(&nd, flags);
+	s = path_init(dirfd, &nd, flags);
 	if (IS_ERR(s))
 		return PTR_ERR(s);
 
@@ -2345,13 +2359,13 @@ static int filename_lookup(struct filename *name, unsigned flags,
 	return err;
 }
 
-static struct fs_device *get_fsdevice_by_path(const char *pathname)
+static struct fs_device *get_fsdevice_by_path(int dirfd, const char *pathname)
 {
 	struct fs_device *fsdev;
 	struct path path;
 	int ret;
 
-	ret = filename_lookup(getname(pathname), 0, &path);
+	ret = filename_lookup(dirfd, getname(pathname), 0, &path);
 	if (ret)
 		return NULL;
 
@@ -2403,14 +2417,14 @@ static int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 /* libfs.c */
 
 /* ---------------------------------------------------------------- */
-int mkdir (const char *pathname, mode_t mode)
+int mkdirat(int dirfd, const char *pathname, mode_t mode)
 {
 	struct dentry *dentry;
 	struct path path;
 	int error;
 	unsigned int lookup_flags = LOOKUP_DIRECTORY;
 
-	dentry = filename_create(getname(pathname), &path, lookup_flags);
+	dentry = filename_create(dirfd, getname(pathname), &path, lookup_flags);
 	if (IS_ERR(dentry)) {
 		error = PTR_ERR(dentry);
 		goto out;
@@ -2423,9 +2437,9 @@ int mkdir (const char *pathname, mode_t mode)
 out:
 	return errno_set(error);
 }
-EXPORT_SYMBOL(mkdir);
+EXPORT_SYMBOL(mkdirat);
 
-int rmdir (const char *pathname)
+static int rmdirat(int dirfd, const char *pathname)
 {
 	int error = 0;
 	struct filename *name;
@@ -2434,7 +2448,7 @@ int rmdir (const char *pathname)
 	struct qstr last;
 	int type;
 
-	name = filename_parentat(getname(pathname), 0,
+	name = filename_parentat(dirfd, getname(pathname), 0,
 				&path, &last, &type);
 	if (IS_ERR(name))
 		return PTR_ERR(name);
@@ -2475,9 +2489,8 @@ out:
 
 	return errno_set(error);
 }
-EXPORT_SYMBOL(rmdir);
 
-int open(const char *pathname, int flags, ...)
+int openat(int dirfd, const char *pathname, int flags)
 {
 	struct fs_device *fsdev;
 	struct fs_driver *fsdrv;
@@ -2491,7 +2504,7 @@ int open(const char *pathname, int flags, ...)
 	struct filename *filename;
 
 	if (flags & O_TMPFILE) {
-		fsdev = get_fsdevice_by_path(pathname);
+		fsdev = get_fsdevice_by_path(dirfd, pathname);
 		if (!fsdev) {
 			errno = ENOENT;
 			return -errno;
@@ -2525,7 +2538,7 @@ int open(const char *pathname, int flags, ...)
 
 	set_nameidata(&nd, filename);
 
-	s = path_init(&nd, LOOKUP_FOLLOW);
+	s = path_init(dirfd, &nd, LOOKUP_FOLLOW);
 	if (IS_ERR(s))
 		return PTR_ERR(s);
 
@@ -2592,7 +2605,7 @@ int open(const char *pathname, int flags, ...)
 		goto out1;
 	}
 
-	f->path = xstrdup(pathname);
+	f->path = dpath(dentry, d_root);
 	f->dentry = dentry;
 	f->f_inode = iget(inode);
 	f->flags = flags;
@@ -2631,7 +2644,7 @@ out:
 out1:
 	return errno_set(error);
 }
-EXPORT_SYMBOL(open);
+EXPORT_SYMBOL(openat);
 
 static const char *fd_getpath(int fd)
 {
@@ -2647,14 +2660,19 @@ static const char *fd_getpath(int fd)
 	return f->path;
 }
 
-int unlink(const char *pathname)
+int unlinkat(int dirfd, const char *pathname, int flags)
 {
 	int ret;
 	struct dentry *dentry;
 	struct inode *inode;
 	struct path path;
 
-	ret = filename_lookup(getname(pathname), 0, &path);
+	if (flags == AT_REMOVEDIR)
+		return rmdirat(dirfd, pathname);
+	if (flags)
+		return -EINVAL;
+
+	ret = filename_lookup(dirfd, getname(pathname), 0, &path);
 	if (ret)
 		goto out;
 
@@ -2683,7 +2701,7 @@ out_put:
 out:
 	return errno_set(ret);
 }
-EXPORT_SYMBOL(unlink);
+EXPORT_SYMBOL(unlinkat);
 
 static int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
 {
@@ -2700,7 +2718,7 @@ int symlink(const char *pathname, const char *newpath)
 	int error;
 	unsigned int lookup_flags = LOOKUP_DIRECTORY;
 
-	dentry = filename_create(getname(newpath), &path, lookup_flags);
+	dentry = filename_create(AT_FDCWD, getname(newpath), &path, lookup_flags);
 	if (IS_ERR(dentry)) {
 		error = PTR_ERR(dentry);
 		goto out;
@@ -2757,7 +2775,7 @@ DIR *opendir(const char *pathname)
 	DIR *d;
 	struct path path = {};
 
-	ret = filename_lookup(getname(pathname),
+	ret = filename_lookup(AT_FDCWD, getname(pathname),
 			      LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
 	if (ret)
 		goto out;
@@ -2844,7 +2862,7 @@ int rewinddir(DIR *dir)
 }
 EXPORT_SYMBOL(rewinddir);
 
-int readlink(const char *pathname, char *buf, size_t bufsiz)
+int readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz)
 {
 	int ret;
 	struct dentry *dentry;
@@ -2852,7 +2870,7 @@ int readlink(const char *pathname, char *buf, size_t bufsiz)
 	const char *link;
 	struct path path = {};
 
-	ret = filename_lookup(getname(pathname), 0, &path);
+	ret = filename_lookup(dirfd, getname(pathname), 0, &path);
 	if (ret)
 		goto out;
 
@@ -2884,16 +2902,16 @@ out_put:
 out:
 	return errno_set(ret);
 }
-EXPORT_SYMBOL(readlink);
+EXPORT_SYMBOL(readlinkat);
 
-static int stat_filename(const char *filename, struct stat *s, unsigned int flags)
+static int stat_filename(int dirfd, const char *filename, struct stat *s, unsigned int flags)
 {
 	int ret;
 	struct dentry *dentry;
 	struct inode *inode;
 	struct path path = {};
 
-	ret = filename_lookup(getname(filename), flags, &path);
+	ret = filename_lookup(dirfd, getname(filename), flags, &path);
 	if (ret)
 		goto out;
 
@@ -2915,17 +2933,17 @@ out:
 	return errno_set(ret);
 }
 
-int stat(const char *filename, struct stat *s)
+int statat(int dirfd, const char *filename, struct stat *s)
 {
-	return stat_filename(filename, s, LOOKUP_FOLLOW);
+	return stat_filename(dirfd, filename, s, LOOKUP_FOLLOW);
 }
-EXPORT_SYMBOL(stat);
+EXPORT_SYMBOL(statat);
 
-int lstat(const char *filename, struct stat *s)
+int lstatat(int dirfd, const char *filename, struct stat *s)
 {
-	return stat_filename(filename, s, 0);
+	return stat_filename(dirfd, filename, s, 0);
 }
-EXPORT_SYMBOL(lstat);
+EXPORT_SYMBOL(lstatat);
 
 static char *__dpath(struct dentry *dentry, struct dentry *root)
 {
@@ -2981,6 +2999,8 @@ char *dpath(struct dentry *dentry, struct dentry *root)
 
 /**
  * canonicalize_path - resolve links in path
+ *
+ * @dirfd: directory file descriptor to look up relative to
  * @pathname: The input path
  *
  * This function resolves all links in @pathname and returns
@@ -2988,13 +3008,13 @@ char *dpath(struct dentry *dentry, struct dentry *root)
  *
  * Return: Path with links resolved. Allocated, must be freed after use.
  */
-char *canonicalize_path(const char *pathname)
+char *canonicalize_path(int dirfd, const char *pathname)
 {
 	char *res = NULL;
 	struct path path;
 	int ret;
 
-	ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW, &path);
+	ret = filename_lookup(dirfd, getname(pathname), LOOKUP_FOLLOW, &path);
 	if (ret)
 		goto out;
 
@@ -3016,7 +3036,7 @@ int chdir(const char *pathname)
 	struct path path;
 	int ret;
 
-	ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
+	ret = filename_lookup(AT_FDCWD, getname(pathname), LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
 	if (ret)
 		goto out;
 
@@ -3135,7 +3155,7 @@ int mount(const char *device, const char *fsname, const char *pathname,
 	struct path path = {};
 
 	if (d_root) {
-		ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW, &path);
+		ret = filename_lookup(AT_FDCWD, getname(pathname), LOOKUP_FOLLOW, &path);
 		if (ret)
 			goto out;
 
@@ -3242,7 +3262,7 @@ int umount(const char *pathname)
 	struct path path = {};
 	int ret;
 
-	ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW, &path);
+	ret = filename_lookup(AT_FDCWD, getname(pathname), LOOKUP_FOLLOW, &path);
 	if (ret)
 		return ret;
 
@@ -3313,7 +3333,7 @@ void automount_remove(const char *pathname)
 	struct path path;
 	int ret;
 
-	ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW, &path);
+	ret = filename_lookup(AT_FDCWD, getname(pathname), LOOKUP_FOLLOW, &path);
 	if (ret)
 		return;
 
@@ -3329,7 +3349,7 @@ int automount_add(const char *pathname, const char *cmd)
 	struct path path;
 	int ret;
 
-	ret = filename_lookup(getname(pathname), LOOKUP_FOLLOW, &path);
+	ret = filename_lookup(AT_FDCWD, getname(pathname), LOOKUP_FOLLOW, &path);
 	if (ret)
 		return ret;
 
@@ -3441,14 +3461,14 @@ static int do_lookup_dentry(int argc, char *argv[])
 	if (argc < 2)
 		return COMMAND_ERROR_USAGE;
 
-	ret = filename_lookup(getname(argv[1]), 0, &path);
+	ret = filename_lookup(AT_FDCWD, getname(argv[1]), 0, &path);
 	if (ret) {
 		printf("Cannot lookup path \"%s\": %s\n",
 		       argv[1], strerror(-ret));
 		return 1;
 	}
 
-	canon = canonicalize_path(argv[1]);
+	canon = canonicalize_path(AT_FDCWD, argv[1]);
 
 	printf("path \"%s\":\n", argv[1]);
 	printf("dentry: 0x%p\n", path.dentry);