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drm: count a display whose frames never match its advertised size

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The display list carries the CRTC mode and a frame carries the scanout
framebuffer. Those are two different numbers whenever a CRTC scales a
smaller buffer up to its mode, so such a display fails the geometry guard
on the FIRST frame of every session, having delivered nothing.

That path marked the session as having produced frames, which is what the
zero-frame streak uses to decide a display cannot be served over DRM at
all. So the demotion to PipeWire never armed and the display rebuilt until
the rapid-rebuild guard caught it seconds later, under a message about a
mid-session change that never happened.

Count it instead, through the same bookkeeping the stream-died path uses
(now one helper, so the two cannot drift), and say which of the two cases
the error is. The unit test asserted the old behaviour on a capturer that
had never delivered a frame, so it is split into the mid-session case it
meant to cover and the first-frame case it was silently locking in.
This commit is contained in:
Mariano Abad
2026-07-28 14:09:14 -03:00
parent e561121806
commit 0b7a657a32
1 changed files with 117 additions and 41 deletions
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158
src/server/drm_capturer.rs
View File

@@ -339,6 +339,46 @@ impl IpcDrmCapturer {
displays,
))
}
/// Record that this session ended without ever handing a usable frame to the encoder. If enough
/// sessions in a row end this way for the same display, its scanout is effectively ungrabbable;
/// counting them is what makes `get_capturer_info()` refuse that display so the video service
/// falls back to PipeWire for it (other displays are unaffected).
///
/// Called from both places a session can end with nothing delivered -- the stream dying, and a
/// first frame whose geometry does not match what the display list advertised -- so the two
/// cannot drift apart.
///
/// No identity means the handshake list did not describe this index, so there is nothing safe to
/// attribute the failure to; skip rather than blame a neighbour. Recording it under the empty key
/// would do exactly that, because an index that cannot be resolved reads back as the same empty
/// key in get_capturer_info: one unidentifiable display would demote the next one.
fn note_session_without_frame(&self) {
let Some(key) = self.connector.clone() else {
log::debug!(
"drm: display {} produced no frame but has no connector identity; \
not counting it against any display",
self.display
);
return;
};
let mut map = DRM_DISPLAY_HEALTH.lock().unwrap();
let h = map.entry(key).or_insert_with(DisplayHealth::new);
h.zero_frame_streak += 1;
h.since = Instant::now();
// Count the demote cycle exactly once, as the streak crosses the threshold.
if h.zero_frame_streak == DRM_GRAB_MAX_FAILURES {
h.demotes += 1;
log::warn!(
"drm: display {} produced no frame in {} sessions; using PipeWire for it, \
retrying DRM in {:?} (demotion {})",
self.display,
h.zero_frame_streak,
demote_cooldown(h.demotes),
h.demotes
);
}
}
}
impl Drop for IpcDrmCapturer {
@@ -372,16 +412,31 @@ impl TraitCapturer for IpcDrmCapturer {
// and convert_to_yuv only refuses a source LARGER than its destination, so a smaller
// frame would be encoded into the old canvas and the stale right and bottom edges
// would stay on screen until the connection was torn down. Fail hard instead, which
// routes a shrink through the same rebuild an enlargement already takes. got_frame is
// set first: this session did produce frames, so it must not be counted as one of the
// zero-frame sessions that demote a display to PipeWire.
// routes a shrink through the same rebuild an enlargement already takes.
//
// If this is the FIRST frame of the session the size never changed: the advertised
// geometry and the frames simply disagree. They come from different places -- the
// display list carries the CRTC mode (`crtc->mode.hdisplay`) while a frame carries
// the scanout framebuffer (`fb2->width`), and a CRTC that scales a smaller buffer up
// to its mode makes those two permanently different numbers. That display cannot be
// served over DRM at all, so count it as a session that produced nothing and let the
// usual streak demote it to PipeWire. Marking it as having produced frames instead
// would leave only the rapid-rebuild guard to catch it, several seconds later and
// under a message about a change that never happened.
if self.session_size.is_some_and(|(sw, sh)| (w, h) != (sw, sh)) {
self.got_frame = true;
if !self.got_frame {
self.note_session_without_frame();
}
let (sw, sh) = self.session_size.unwrap_or_default();
let what = if self.got_frame {
"changed geometry mid-session"
} else {
"never matched its advertised geometry"
};
return Err(io::Error::new(
io::ErrorKind::Other,
format!(
"drm: display {} changed geometry mid-session ({sw}x{sh} -> {w}x{h}); rebuilding",
"drm: display {} {what} ({sw}x{sh} -> {w}x{h}); rebuilding",
self.display
),
));
@@ -408,39 +463,7 @@ impl TraitCapturer for IpcDrmCapturer {
.clone()
.unwrap_or_else(|| "drm stream ended".to_owned());
if !self.got_frame {
// This session never produced a frame for THIS display. If enough sessions in a
// row fail this way for the same display, its scanout is effectively ungrababble;
// count it so get_capturer_info() will refuse that display and the video service
// falls back to PipeWire for it (other displays are unaffected).
// No identity means the handshake list did not describe this index, so there is
// nothing safe to attribute the failure to; skip rather than blame a neighbour.
// Recording it under the empty key would do exactly that, because an index that
// cannot be resolved reads back as the same empty key in get_capturer_info: one
// unidentifiable display would demote the next one.
if let Some(key) = self.connector.clone() {
let mut map = DRM_DISPLAY_HEALTH.lock().unwrap();
let h = map.entry(key).or_insert_with(DisplayHealth::new);
h.zero_frame_streak += 1;
h.since = Instant::now();
// Count the demote cycle exactly once, as the streak crosses the threshold.
if h.zero_frame_streak == DRM_GRAB_MAX_FAILURES {
h.demotes += 1;
log::warn!(
"drm: display {} produced no frame in {} sessions; using PipeWire for it, \
retrying DRM in {:?} (demotion {})",
self.display,
h.zero_frame_streak,
demote_cooldown(h.demotes),
h.demotes
);
}
} else {
log::debug!(
"drm: display {} produced no frame but has no connector identity; \
not counting it against any display",
self.display
);
}
self.note_session_without_frame();
}
return Err(io::Error::new(io::ErrorKind::Other, err));
}
@@ -1535,6 +1558,14 @@ mod drm_capturer_tests {
// `shared`, so a test can put a frame there directly and drive `frame()` exactly as the encoder
// loop does.
fn capturer_with(session: Option<(usize, usize)>) -> IpcDrmCapturer {
capturer_named(session, None)
}
// A capturer with a connector identity, so the per-display health bookkeeping actually has
// somewhere to record. DRM_DISPLAY_HEALTH is process-wide and the test binary runs threads in
// parallel, so every test that inspects it must pass its OWN key.
fn capturer_named(session: Option<(usize, usize)>, key: Option<&str>) -> IpcDrmCapturer {
let connector = key.map(|k| k.to_owned());
IpcDrmCapturer {
shared: Arc::new(Shared {
slot: Mutex::new(FrameSlot {
@@ -1546,7 +1577,7 @@ mod drm_capturer_tests {
}),
stop: Arc::new(AtomicBool::new(false)),
display: 0,
connector: None,
connector,
session_size: session,
cur: Vec::new(),
cur_w: 0,
@@ -1556,6 +1587,17 @@ mod drm_capturer_tests {
}
}
// The zero-frame streak recorded against this capturer's display, 0 when nothing was recorded.
fn zero_frame_streak_of(c: &IpcDrmCapturer) -> u32 {
let key = c.connector.clone().expect("this check needs an identity");
DRM_DISPLAY_HEALTH
.lock()
.unwrap()
.get(&key)
.map(|h| h.zero_frame_streak)
.unwrap_or(0)
}
// Publishes exactly the way the receive path does, so the recycling is exercised too: take a
// free buffer if one is on offer, fill it, publish it.
fn put_frame(c: &IpcDrmCapturer, w: usize, h: usize) {
@@ -1582,7 +1624,11 @@ mod drm_capturer_tests {
// into the old canvas and the stale edges stay on screen for the rest of the connection.
#[test]
fn a_smaller_frame_ends_the_session_instead_of_being_encoded() {
let mut c = capturer_with(Some((1920, 1080)));
let mut c = capturer_named(Some((1920, 1080)), Some("test:mid-session-shrink"));
// Deliver one frame at the session geometry first, so this is a genuine MID-session shrink
// and not a display whose frames never matched what was advertised (covered below).
put_frame(&c, 1920, 1080);
assert!(matches!(c.frame(Duration::from_millis(50)), Ok(_)));
put_frame(&c, 1280, 720);
// `Frame` is not Debug, so match rather than expect_err.
let err = match c.frame(Duration::from_millis(50)) {
@@ -1591,7 +1637,37 @@ mod drm_capturer_tests {
};
assert!(err.to_string().contains("changed geometry mid-session"));
// Sessions that delivered frames must not be counted toward the zero-frame demotion streak.
assert!(c.got_frame, "the rebuild must not look like a display that never produced a frame");
assert!(
c.got_frame,
"the rebuild must not look like a display that never produced a frame"
);
assert_eq!(
zero_frame_streak_of(&c),
0,
"a session that streamed must not be counted as one that produced nothing"
);
}
// The advertised geometry comes from the CRTC mode and a frame comes from the scanout
// framebuffer, so a CRTC that scales a smaller buffer up to its mode makes the two permanently
// different. Every session for such a display then dies on its FIRST frame having delivered
// nothing, which is precisely what the zero-frame streak exists to demote; it must be counted,
// not excused as a mid-session change that never happened.
#[test]
fn a_first_frame_that_never_matched_counts_as_a_session_without_frames() {
let mut c = capturer_named(Some((1920, 1080)), Some("test:never-matched"));
put_frame(&c, 1280, 720);
let err = match c.frame(Duration::from_millis(50)) {
Err(e) => e,
Ok(_) => panic!("a first frame off the advertised geometry must be a hard error"),
};
assert!(err.to_string().contains("never matched its advertised geometry"));
assert!(!c.got_frame, "no frame reached the encoder, so none was produced");
assert_eq!(
zero_frame_streak_of(&c),
1,
"the display must be on its way to a PipeWire demotion, not just rebuilding"
);
}
#[test]