Linux Kernel FileSystems Sub-system - Tracing VFS APIs - vfs_mknod() vfs_mkdir() vfs_rename()
Linux Kernel FileSystems Sub-system - Tracing VFS APIs - vfs_mknod() vfs_mkdir() vfs_rename()

Refer:
Wiki – Virtual file system ↗

Linux Kernel:
fs/namei.c – vfs_mknod(), vfs_mkdir(), vfs_rename() ↗

Here is the source-code from the Kernel-source version 6.5.9 for quick reference:

/**
 * vfs_mknod - create device node or file
 * @idmap:	idmap of the mount the inode was found from
 * @dir:	inode of @dentry
 * @dentry:	pointer to dentry of the base directory
 * @mode:	mode of the new device node or file
 * @dev:	device number of device to create
 *
 * Create a device node or file.
 *
 * If the inode has been found through an idmapped mount the idmap of
 * the vfsmount must be passed through @idmap. This function will then take
 * care to map the inode according to @idmap before checking permissions.
 * On non-idmapped mounts or if permission checking is to be performed on the
 * raw inode simply passs @nop_mnt_idmap.
 */
int vfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
	      struct dentry *dentry, umode_t mode, dev_t dev)
{
	bool is_whiteout = S_ISCHR(mode) && dev == WHITEOUT_DEV;
	int error = may_create(idmap, dir, dentry);

	if (error)
		return error;

	if ((S_ISCHR(mode) || S_ISBLK(mode)) && !is_whiteout &&
	    !capable(CAP_MKNOD))
		return -EPERM;

	if (!dir->i_op->mknod)
		return -EPERM;

	mode = vfs_prepare_mode(idmap, dir, mode, mode, mode);
	error = devcgroup_inode_mknod(mode, dev);
	if (error)
		return error;

	error = security_inode_mknod(dir, dentry, mode, dev);
	if (error)
		return error;

	error = dir->i_op->mknod(idmap, dir, dentry, mode, dev);
	if (!error)
		fsnotify_create(dir, dentry);
	return error;
}
EXPORT_SYMBOL(vfs_mknod);
/**
 * vfs_mkdir - create directory
 * @idmap:	idmap of the mount the inode was found from
 * @dir:	inode of @dentry
 * @dentry:	pointer to dentry of the base directory
 * @mode:	mode of the new directory
 *
 * Create a directory.
 *
 * If the inode has been found through an idmapped mount the idmap of
 * the vfsmount must be passed through @idmap. This function will then take
 * care to map the inode according to @idmap before checking permissions.
 * On non-idmapped mounts or if permission checking is to be performed on the
 * raw inode simply passs @nop_mnt_idmap.
 */
int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
	      struct dentry *dentry, umode_t mode)
{
	int error;
	unsigned max_links = dir->i_sb->s_max_links;

	error = may_create(idmap, dir, dentry);
	if (error)
		return error;

	if (!dir->i_op->mkdir)
		return -EPERM;

	mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, 0);
	error = security_inode_mkdir(dir, dentry, mode);
	if (error)
		return error;

	if (max_links && dir->i_nlink >= max_links)
		return -EMLINK;

	error = dir->i_op->mkdir(idmap, dir, dentry, mode);
	if (!error)
		fsnotify_mkdir(dir, dentry);
	return error;
}
EXPORT_SYMBOL(vfs_mkdir);
/**
 * vfs_rename - rename a filesystem object
 * @rd:		pointer to &struct renamedata info
 *
 * The caller must hold multiple mutexes--see lock_rename()).
 *
 * If vfs_rename discovers a delegation in need of breaking at either
 * the source or destination, it will return -EWOULDBLOCK and return a
 * reference to the inode in delegated_inode.  The caller should then
 * break the delegation and retry.  Because breaking a delegation may
 * take a long time, the caller should drop all locks before doing
 * so.
 *
 * Alternatively, a caller may pass NULL for delegated_inode.  This may
 * be appropriate for callers that expect the underlying filesystem not
 * to be NFS exported.
 *
 * The worst of all namespace operations - renaming directory. "Perverted"
 * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
 * Problems:
 *
 *	a) we can get into loop creation.
 *	b) race potential - two innocent renames can create a loop together.
 *	   That's where 4.4 screws up. Current fix: serialization on
 *	   sb->s_vfs_rename_mutex. We might be more accurate, but that's another
 *	   story.
 *	c) we have to lock _four_ objects - parents and victim (if it exists),
 *	   and source.
 *	   And that - after we got ->i_mutex on parents (until then we don't know
 *	   whether the target exists).  Solution: try to be smart with locking
 *	   order for inodes.  We rely on the fact that tree topology may change
 *	   only under ->s_vfs_rename_mutex _and_ that parent of the object we
 *	   move will be locked.  Thus we can rank directories by the tree
 *	   (ancestors first) and rank all non-directories after them.
 *	   That works since everybody except rename does "lock parent, lookup,
 *	   lock child" and rename is under ->s_vfs_rename_mutex.
 *	   HOWEVER, it relies on the assumption that any object with ->lookup()
 *	   has no more than 1 dentry.  If "hybrid" objects will ever appear,
 *	   we'd better make sure that there's no link(2) for them.
 *	d) conversion from fhandle to dentry may come in the wrong moment - when
 *	   we are removing the target. Solution: we will have to grab ->i_mutex
 *	   in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
 *	   ->i_mutex on parents, which works but leads to some truly excessive
 *	   locking].
 */
int vfs_rename(struct renamedata *rd)
{
	int error;
	struct inode *old_dir = rd->old_dir, *new_dir = rd->new_dir;
	struct dentry *old_dentry = rd->old_dentry;
	struct dentry *new_dentry = rd->new_dentry;
	struct inode **delegated_inode = rd->delegated_inode;
	unsigned int flags = rd->flags;
	bool is_dir = d_is_dir(old_dentry);
	struct inode *source = old_dentry->d_inode;
	struct inode *target = new_dentry->d_inode;
	bool new_is_dir = false;
	unsigned max_links = new_dir->i_sb->s_max_links;
	struct name_snapshot old_name;

	if (source == target)
		return 0;

	error = may_delete(rd->old_mnt_idmap, old_dir, old_dentry, is_dir);
	if (error)
		return error;

	if (!target) {
		error = may_create(rd->new_mnt_idmap, new_dir, new_dentry);
	} else {
		new_is_dir = d_is_dir(new_dentry);

		if (!(flags & RENAME_EXCHANGE))
			error = may_delete(rd->new_mnt_idmap, new_dir,
					   new_dentry, is_dir);
		else
			error = may_delete(rd->new_mnt_idmap, new_dir,
					   new_dentry, new_is_dir);
	}
	if (error)
		return error;

	if (!old_dir->i_op->rename)
		return -EPERM;

	/*
	 * If we are going to change the parent - check write permissions,
	 * we'll need to flip '..'.
	 */
	if (new_dir != old_dir) {
		if (is_dir) {
			error = inode_permission(rd->old_mnt_idmap, source,
						 MAY_WRITE);
			if (error)
				return error;
		}
		if ((flags & RENAME_EXCHANGE) && new_is_dir) {
			error = inode_permission(rd->new_mnt_idmap, target,
						 MAY_WRITE);
			if (error)
				return error;
		}
	}

	error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
				      flags);
	if (error)
		return error;

	take_dentry_name_snapshot(&old_name, old_dentry);
	dget(new_dentry);
	/*
	 * Lock all moved children. Moved directories may need to change parent
	 * pointer so they need the lock to prevent against concurrent
	 * directory changes moving parent pointer. For regular files we've
	 * historically always done this. The lockdep locking subclasses are
	 * somewhat arbitrary but RENAME_EXCHANGE in particular can swap
	 * regular files and directories so it's difficult to tell which
	 * subclasses to use.
	 */
	lock_two_inodes(source, target, I_MUTEX_NORMAL, I_MUTEX_NONDIR2);

	error = -EPERM;
	if (IS_SWAPFILE(source) || (target && IS_SWAPFILE(target)))
		goto out;

	error = -EBUSY;
	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
		goto out;

	if (max_links && new_dir != old_dir) {
		error = -EMLINK;
		if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
			goto out;
		if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
		    old_dir->i_nlink >= max_links)
			goto out;
	}
	if (!is_dir) {
		error = try_break_deleg(source, delegated_inode);
		if (error)
			goto out;
	}
	if (target && !new_is_dir) {
		error = try_break_deleg(target, delegated_inode);
		if (error)
			goto out;
	}
	error = old_dir->i_op->rename(rd->new_mnt_idmap, old_dir, old_dentry,
				      new_dir, new_dentry, flags);
	if (error)
		goto out;

	if (!(flags & RENAME_EXCHANGE) && target) {
		if (is_dir) {
			shrink_dcache_parent(new_dentry);
			target->i_flags |= S_DEAD;
		}
		dont_mount(new_dentry);
		detach_mounts(new_dentry);
	}
	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
		if (!(flags & RENAME_EXCHANGE))
			d_move(old_dentry, new_dentry);
		else
			d_exchange(old_dentry, new_dentry);
	}
out:
	inode_unlock(source);
	if (target)
		inode_unlock(target);
	dput(new_dentry);
	if (!error) {
		fsnotify_move(old_dir, new_dir, &old_name.name, is_dir,
			      !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
		if (flags & RENAME_EXCHANGE) {
			fsnotify_move(new_dir, old_dir, &old_dentry->d_name,
				      new_is_dir, NULL, new_dentry);
		}
	}
	release_dentry_name_snapshot(&old_name);

	return error;
}
EXPORT_SYMBOL(vfs_rename);