lib/9pfs: Return ENOTSUP on ioctl requests

Currently `9pfs` returns 0 for any `ioctl` request (except for
`TIOCGWINSZ`), which leads to multiple cases of files being interpreted
as terminals. You can see this problem when running python scripts,
since python uses `ioctl` calls to check if it should open up the
interactive interpretor or execute a script.

Same thing could happen for other applications that rely on `ioctl`
operations being properly executed, so the best way to go would be
return `ENOTSUP` (as is used to happen before commit 28d0edf).

If the `ioctl` call always return `ENOTSUP`, the Ruby binary
compatibility application will fail, since it tries to set O_ASYNC and
breaks on error, even if it does not directly depends on that, so for
now add a special case for that.

Signed-off-by: Stefan Jumarea <[email protected]>
Reviewed-by: Sergiu Moga <[email protected]>
Approved-by: Simon Kuenzer <[email protected]>
GitHub-Closes: unikraft#1098

lib/9pfs/9pfs_vnops.c

@@ -1016,10 +1016,23 @@ static int uk_9pfs_ioctl(struct vnode *dvp, struct vfscore_file *fp,
 			 unsigned long com, void *data)
 {
 	switch (com) {
-	case TIOCGWINSZ:
-		return ENOTTY;
-	default:
+	/**
+	 * HACK: In binary compatibility mode, Ruby tries to set O_ASYNC,
+	 * which Unikraft does not yet support. If the `ioctl` call returns
+	 * an error, Ruby stops working, even if it does not depend on the
+	 * O_ASYNC being properly set.
+	 *
+	 * Until proper support, just return 0 in case an `FIONBIO` ioctl
+	 * request is done, and ENOTSUP for all other cases.
+	 *
+	 * Setting `ioctl` to a nullop will not work, since it is used by
+	 * interpreted languages (e.g. python3) to check if it should start
+	 * the interpretor or just read a file.
+	 */
+	case FIONBIO:
 		return 0;
+	default:
+		return ENOTSUP;
 	}
 }