Add (fake) symlink support

[mkst]

exfat-nofuse supports symlinks.

It doesn't look too difficult to port over the code from nofuse that handles symlinks.

Non-exhaustive list of changes:

• [ ] Add definitions for TYPE_SYMLINK and ATTR_SYMLINK to exfat_fs.h and exfat_raw.h
• [ ] Add target to exfat_inode_info struct (?)
• [ ] Update exfat_set_entry_type to set attributes when encountering a symlink
• [ ] Update exfat_make_mode in exfat_super.h
• [ ] Add exfat_symlink_inode_operations in file.c along with definitions of exfat_follow_link / exfat_get_link
• [ ] Update exfat_fill_inode in inode.c to call exfat_symlink_inode_operations when dealing with a symlink
• [ ] Add exfat_symlink to namei.c to handle symlink creation
• [ ] Update inode_operations to add .symlink
• [ ] Update exfat_lookup to handle symlinks
• [ ] Anything that is missing from this list...

I'm hacking my way through the list, if I get to the point where I can get symlinks to work I'll raise a PR. If anyone wants to tackle this in the meantime, that would be swell :)

[arter97]

Previous branch from this also supports symlink.

It's left out this time to stay more inline with upstream's code and exFAT standard itself.

If you absolutely need symlink support, try out the old branch.

[mkst]

old branch gives me the same response as 5.4 kernel:

ln: failed to create symbolic link 'bar': Unknown error 524

Is there a specific revision of the old branch I should be trying?

[arter97]

Did you use the symlink mount option?

[mkst]

Aha. symlink=1 sorted it. Thankyou!

[piranna]

What's the reason to don't have the symlinks feature behing a flag, both here or upstream? In fact, symlink hack could be used in all FAT filesystems in upstream kernel...

[arter97]

https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/drivers/staging/exfat?h=main&id=bb9397a356c6cc9a6e1d45633476fe83cf15a95f