backends/drm: fetch immutable blobs in DrmProperty

If the blob is fetched while there is no kernel-visible reference to it,
the driver may re-use the blob ID. When DrmProperty is created or updated,
KWin holds a reference on the blob via drmModeObjectProperties, so this
should prevent any possible issues.

CCBUG: 449285

src/backends/drm/drm_object_connector.cpp

@@ -312,16 +312,11 @@ bool DrmConnector::updateProperties()
     }
 
     // parse edid
-    auto edidProp = getProp(PropertyIndex::Edid);
-    if (edidProp) {
-        DrmScopedPointer<drmModePropertyBlobRes> blob(drmModeGetPropertyBlob(gpu()->fd(), edidProp->current()));
-        if (blob && blob->data) {
-            m_edid = Edid(blob->data, blob->length);
-            if (!m_edid.isValid()) {
-                qCWarning(KWIN_DRM) << "Couldn't parse EDID for connector" << this;
-            }
+    if (const auto edidProp = getProp(PropertyIndex::Edid); edidProp && edidProp->immutableBlob()) {
+        m_edid = Edid(edidProp->immutableBlob()->data, edidProp->immutableBlob()->length);
+        if (!m_edid.isValid()) {
+            qCWarning(KWIN_DRM) << "Couldn't parse EDID for connector" << this;
         }
-        deleteProp(PropertyIndex::Edid);
     } else {
         qCDebug(KWIN_DRM) << "Could not find edid for connector" << this;
     }

src/backends/drm/drm_object_plane.cpp

@@ -67,29 +67,26 @@ bool DrmPlane::init()
         checkSupport(5, Transformation::ReflectY);
 
         // read formats from blob if available and if modifiers are supported, and from the plane object if not
-        if (auto formatProp = getProp(PropertyIndex::In_Formats); formatProp && gpu()->addFB2ModifiersSupported()) {
-            DrmScopedPointer<drmModePropertyBlobRes> propertyBlob(drmModeGetPropertyBlob(gpu()->fd(), formatProp->current()));
-            if (propertyBlob && propertyBlob->data) {
-                auto blob = static_cast<drm_format_modifier_blob *>(propertyBlob->data);
-                auto modifiers = reinterpret_cast<drm_format_modifier *>(reinterpret_cast<uint8_t *>(blob) + blob->modifiers_offset);
-                uint32_t *formatarr = reinterpret_cast<uint32_t *>(reinterpret_cast<uint8_t *>(blob) + blob->formats_offset);
+        if (const auto formatProp = getProp(PropertyIndex::In_Formats); formatProp && formatProp->immutableBlob() && gpu()->addFB2ModifiersSupported()) {
+            auto blob = static_cast<drm_format_modifier_blob *>(formatProp->immutableBlob()->data);
+            auto modifiers = reinterpret_cast<drm_format_modifier *>(reinterpret_cast<uint8_t *>(blob) + blob->modifiers_offset);
+            uint32_t *formatarr = reinterpret_cast<uint32_t *>(reinterpret_cast<uint8_t *>(blob) + blob->formats_offset);
 
-                for (uint32_t f = 0; f < blob->count_formats; f++) {
-                    auto format = formatarr[f];
-                    QVector<uint64_t> mods;
-                    for (uint32_t m = 0; m < blob->count_modifiers; m++) {
-                        auto modifier = &modifiers[m];
-                        // The modifier advertisement blob is partitioned into groups of 64 formats
-                        if (m < modifier->offset || m > modifier->offset + 63) {
-                            continue;
-                        }
-                        if (!(modifier->formats & (1 << (f - modifier->offset)))) {
-                            continue;
-                        }
-                        mods << modifier->modifier;
+            for (uint32_t f = 0; f < blob->count_formats; f++) {
+                auto format = formatarr[f];
+                QVector<uint64_t> mods;
+                for (uint32_t m = 0; m < blob->count_modifiers; m++) {
+                    auto modifier = &modifiers[m];
+                    // The modifier advertisement blob is partitioned into groups of 64 formats
+                    if (m < modifier->offset || m > modifier->offset + 63) {
+                        continue;
                     }
-                    m_supportedFormats.insert(format, mods);
+                    if (!(modifier->formats & (1 << (f - modifier->offset)))) {
+                        continue;
+                    }
+                    mods << modifier->modifier;
                 }
+                m_supportedFormats.insert(format, mods);
             }
         } else {
             for (uint32_t i = 0; i < p->count_formats; i++) {

src/backends/drm/drm_property.cpp

@@ -24,6 +24,7 @@ DrmProperty::DrmProperty(DrmObject *obj, drmModePropertyRes *prop, uint64_t val,
     , m_next(val)
     , m_current(val)
     , m_immutable(prop->flags & DRM_MODE_PROP_IMMUTABLE)
+    , m_isBlob(prop->flags & DRM_MODE_PROP_BLOB)
     , m_obj(obj)
 {
     if (!enumNames.isEmpty()) {
@@ -35,6 +36,7 @@ DrmProperty::DrmProperty(DrmObject *obj, drmModePropertyRes *prop, uint64_t val,
         m_minValue = prop->values[0];
         m_maxValue = prop->values[1];
     }
+    updateBlob();
 }
 
 DrmProperty::~DrmProperty() = default;
@@ -110,7 +112,10 @@ bool DrmProperty::needsCommit() const
 
 void DrmProperty::setCurrent(uint64_t value)
 {
-    m_current = value;
+    if (m_current != value) {
+        updateBlob();
+        m_current = value;
+    }
 }
 
 uint64_t DrmProperty::current() const
@@ -122,10 +127,12 @@ QVector<QByteArray> DrmProperty::enumNames() const
 {
     return m_enumNames;
 }
+
 bool DrmProperty::hasEnum(uint64_t value) const
 {
     return m_enumMap.contains(value);
 }
+
 bool DrmProperty::hasAllEnums() const
 {
     return m_enumMap.count() == m_enumNames.count();
@@ -166,4 +173,22 @@ uint64_t DrmProperty::maxValue() const
     return m_maxValue;
 }
 
+void DrmProperty::updateBlob()
+{
+    if (m_immutable && m_isBlob) {
+        if (m_current != 0) {
+            m_immutableBlob.reset(drmModeGetPropertyBlob(m_obj->gpu()->fd(), m_current));
+            if (m_immutableBlob && (!m_immutableBlob->data || !m_immutableBlob->length)) {
+                m_immutableBlob.reset();
+            }
+        } else {
+            m_immutableBlob.reset();
+        }
+    }
+}
+
+drmModePropertyBlobRes *DrmProperty::immutableBlob() const
+{
+    return m_immutableBlob.get();
+}
 }

src/backends/drm/drm_property.h

@@ -9,9 +9,9 @@
 */
 
 #pragma once
+#include "drm_pointer.h"
 
 #include <xf86drmMode.h>
-
 #include <QByteArray>
 #include <QMap>
 #include <QVector>
@@ -61,6 +61,7 @@ public:
 
     void setCurrent(uint64_t value);
     uint64_t current() const;
+    drmModePropertyBlobRes *immutableBlob() const;
 
     uint64_t minValue() const;
     uint64_t maxValue() const;
@@ -81,6 +82,8 @@ public:
     }
 
 private:
+    void updateBlob();
+
     uint32_t m_propId = 0;
     QByteArray m_propName;
 
@@ -92,6 +95,7 @@ private:
     uint64_t m_next = 0;
     // the value currently set for or by the kernel
     uint64_t m_current = 0;
+    DrmScopedPointer<drmModePropertyBlobRes> m_immutableBlob;
 
     uint64_t m_minValue = -1;
     uint64_t m_maxValue = -1;
@@ -99,6 +103,7 @@ private:
     QMap<uint32_t, uint64_t> m_enumMap;
     QVector<QByteArray> m_enumNames;
     const bool m_immutable;
+    const bool m_isBlob;
     bool m_legacy = false;
     const DrmObject *m_obj;
 };