I don't think this is possible with the default kernel driver (
fs/hfsplus in the kernel sources).
I have an HFS+ volume mounted in Linux and files that have a resource fork. I tried both the commonly-used special filename syntaxes
FILENAME/..namedfork/rsrc. The former used to work on Mac OS, and the latter works on Mac OS now, but neither works on Linux. They return the error
ENOTDIR, "Not a directory". I tried this with files that have a resource fork and no data fork, and files that have both.
I looked through the driver sources and I can see no sign of it being possible to access a resource fork explicitly, either with a special filename syntax or with an
ioctl call. The driver does concern itself with resource forks, but only for the purpose of keeping them together with the rest of the file when a file is moved, and deleting them when a file is deleted.
I would love to be proved wrong on this, but I wasn't able to find any information to the contrary.