ask-password: add support for caching passwords in the kernel keyring

This adds support for caching harddisk passwords in the kernel keyring
if it is available, thus supporting caching without Plymouth being
around.

This is also useful for hooking up "gdm-auto-login" with the collected
boot-time harddisk password, in order to support gnome keyring
passphrase unlocking via the HDD password, if it is the same.

Any passwords added to the kernel keyring this way have a timeout of
2.5min at which time they are purged from the kernel.

src/basic/missing.h

@@ -1063,3 +1063,48 @@ static inline int kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, uns
 #ifndef INPUT_PROP_ACCELEROMETER
 #define INPUT_PROP_ACCELEROMETER  0x06
 #endif
+
+#if !HAVE_DECL_KEY_SERIAL_T
+typedef int32_t key_serial_t;
+#endif
+
+#if !HAVE_DECL_KEYCTL
+static inline long keyctl(int cmd, unsigned long arg2, unsigned long arg3, unsigned long arg4,unsigned long arg5) {
+#if defined(__NR_keyctl)
+        return syscall(__NR_keyctl, cmd, arg2, arg3, arg4, arg5);
+#else
+        errno = ENOSYS;
+        return -1;
+#endif
+}
+
+static inline key_serial_t add_key(const char *type, const char *description, const void *payload, size_t plen, key_serial_t ringid) {
+#if defined (__NR_add_key)
+        return syscall(__NR_add_key, type, description, payload, plen, ringid);
+#else
+        errno = ENOSYS;
+        return -1;
+#endif
+}
+
+static inline key_serial_t request_key(const char *type, const char *description, const char * callout_info, key_serial_t destringid) {
+#if defined (__NR_request_key)
+        return syscall(__NR_request_key, type, description, callout_info, destringid);
+#else
+        errno = ENOSYS;
+        return -1;
+#endif
+}
+#endif
+
+#ifndef KEYCTL_READ
+#define KEYCTL_READ 11
+#endif
+
+#ifndef KEYCTL_SET_TIMEOUT
+#define KEYCTL_SET_TIMEOUT 15
+#endif
+
+#ifndef KEY_SPEC_USER_KEYRING
+#define KEY_SPEC_USER_KEYRING -4
+#endif