Re: [PATCH 29/38] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #10]

David Howells
2018-07-27T22:27:39Z

Andy Lutomirski <luto@amacapital.net> wrote:

> > [*] Not without a 6-arg syscall or some other way of passing it.
>
> Are there still architectures that have problems with 6-arg syscalls?

As I understand it, 6-arg syscalls are frowned upon.

> I suppose that, as long as there is never a case where fsconfig_set_path and
> fsconfig_set_fd both succeed, then it's not a big deal.

fsconfig_set_path/path_empty requires the 'value' argument to point to a
string, possibly "", and fsconfig_set_fd requires it to be NULL.

I can't stop you from doing:

fd = open("/some/path", O_PATH);
fsconfig(fsfd, fsconfig_set_fd, "fd", NULL, fd);

or:

fd = open("/dev/sda6", O_RDWR);
fsconfig(fsfd, fsconfig_set_path_empty, "foo", "", fd);

The first should fail because I'm using fget() not fget_raw() and the
second will pass the string and fd number to the filesystem, which will
presumably then call fs_lookup_param() to invoke pathwalk upon it - which will
likely also fail.

David