[PATCH proxmox-backup] tape: virtual drive: fix endless recursion in changer status

[Jakob-Tobias Winter <tobias@stuttgart.de>]

The virtual tape drive, which exists for tests and debugging only, also
acts as its own changer and reports every virtual tape in its directory
as a slot. To build that status it asked for the list of online media,
but got the generic variant of that list, which is derived from the
changer status. The two called each other until the stack overflowed, so
every operation that needs the changer status of a virtual drive, like
loading or unloading a tape, crashed the process.

Use the list of tapes in the directory of the drive instead, as it was
intended, for the status and for loading a tape from a slot.

Signed-off-by: Jakob-Tobias Winter <tobias@stuttgart.de>
---
The recursion has been there since 46a1863f8 ("tape: improve MediaChange
trait").

Reproducer, with a virtual drive 'vtape' in tape.cfg and an empty file
'tape-demo1.json' in its directory:

  proxmox-backup-debug api create /tape/drive/vtape/load-slot \
      --source-slot 1

Tested with debug builds of current master and of 4.2.8, calling the API
in-process (PROXMOX_DEBUG_API_CODE=1): the call aborts with a stack
overflow without the patch and loads the tape with it.

 src/tape/drive/virtual_tape.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/tape/drive/virtual_tape.rs b/src/tape/drive/virtual_tape.rs
index a17916bab..b2febaed5 100644
--- a/src/tape/drive/virtual_tape.rs
+++ b/src/tape/drive/virtual_tape.rs
@@ -499,7 +499,7 @@ impl MediaChange for VirtualTapeHandle {
         // slot-assignment here.
 
         let mut slots = Vec::new();
-        let label_texts = self.online_media_label_texts()?;
+        let label_texts = VirtualTapeHandle::online_media_label_texts(self)?;
         let max_slots = label_texts.len().div_ceil(8) * 8;
 
         for i in 0..max_slots {
@@ -535,7 +535,7 @@ impl MediaChange for VirtualTapeHandle {
             bail!("invalid slot ID {}", slot);
         }
 
-        let label_texts = self.online_media_label_texts()?;
+        let label_texts = VirtualTapeHandle::online_media_label_texts(self)?;
 
         if slot > label_texts.len() as u64 {
             bail!("slot {} is empty", slot);
-- 
2.53.0