On Tue, Apr 11, 2017, at 02:07 PM, Eric Blake wrote:
>
> A good idea on the surface. But reading the man page of openat(), the
> section on O_PATH says:
> The file
> itself is not opened, and other file operations (e.g.,
> read(2),
> write(2), fchmod(2), fchown(2), fgetxattr(2), mmap(2))
> fail with
> the error EBADF.
Right, though more topically I'd have expected
fchmodat() (not fchmod()) to take AT_EMPTY_PATH,
just like fstatat() does.
But it doesn't appear to be supported...oh, even at
the syscall level, interesting. Ah, I see, glibc does:
int
fchmodat (int fd, const char *file, mode_t mode, int flag)
{
if (flag & ~AT_SYMLINK_NOFOLLOW)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
...
}
And indeed the syscall doesn't have flags, bringing us back
to the start here. Sorry, that seems obvious in retrospect,
but I was "working forwards" from the O_PATH userspace API
mindset.
