feat(key): make `UnlockPolicy::Fail` more useful

We already can check if an fs is encrypted with `bcachefs unlock -c`.
With this option we can now instead check if we have a key but not
actually mount by not specifying a mount point. e.g.

```sh
if bcachefs mount -k fail "$blkdev"`; then
    echo "device is unlocked!"
fi
```

Not sure what the original intent for this was. For scenarios where
encryption is simply not supported on principle?

Signed-off-by: Thomas Mühlbacher <tmuehlbacher@posteo.net>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/key.rs b/src/key.rs
index 78f61388..0a2d08da 100644
--- a/src/key.rs
+++ b/src/key.rs
@@ -25,7 +25,8 @@ const BCH_KEY_MAGIC: &str = "bch**key";
 
 #[derive(Clone, Debug, clap::ValueEnum, strum::Display)]
 pub enum UnlockPolicy {
-    /// Don't ask for passphrase, fail if filesystem is encrypted
+    /// Don't ask for passphrase, if the key cannot be found in the keyring just
+    /// fail
     Fail,
     /// Wait for passphrase to become available before mounting
     Wait,
@@ -42,7 +43,7 @@ impl UnlockPolicy {
         info!("Using filesystem unlock policy '{self}' on {uuid}");
 
         match self {
-            Self::Fail => Err(anyhow!("no passphrase available")),
+            Self::Fail => KeyHandle::new_from_search(&uuid),
             Self::Wait => Ok(KeyHandle::wait_for_unlock(&uuid)?),
             Self::Ask => Passphrase::new_from_prompt().and_then(|p| KeyHandle::new(sb, &p)),
             Self::Stdin => Passphrase::new_from_stdin().and_then(|p| KeyHandle::new(sb, &p)),