lseek() on entries in /proc/device-tree returns EINVAL

[Timur Tabi <timur@freescale.com>]

I'm writing a utility that parses the device tree in /proc/device-tree, and in
order to read a property into memory, I have to first find out how large it is.
 So I have the following code:

	off_t off;
	int f;

	f = open(filename, O_RDONLY);
	if (f == -1) {
		perror(__func__);
		return NULL;
	}

	off = lseek(f, 0, SEEK_END);
	if (off == -1) {
		perror(__func__);
		goto fail;
	}

The lseek() call returns -1, and errno is set to EINVAL.  According to the man
page, this means:

       EINVAL The  whence  argument  is  not a proper value, or the resulting
              file offset would be negative for a regular file, block special
              file, or directory.

Is there a limitation for the implementation of /proc/device-tree that prevents
lseek() from working?  If so, how do I determine the size of a property?

-- 
Timur Tabi
Linux kernel developer at Freescale