logd: refactor mLast setting into a GetOldest function
This code was duplicated throughout LogBuffer.cpp, so refactor it into
a single location and clean up some comments along the way.
This may fix a subtle bug: if `logcat -c` is used from a
non-privileged UID, the current code may set mLast to the oldest seen
log message *from that UID* and not not the oldest log message for
that log id. That may prevent pruning from the start of that log,
resulting in old log entries that are impossible to delete.
Bug: 144382260
Test: logging works, and above scenario is not seen
Change-Id: I1749293ce6ea1697dd8a9258cfd7eab29dbeac6e
diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index 16225a5..458fbbb 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -20,6 +20,7 @@
#include <sys/types.h>
#include <list>
+#include <optional>
#include <string>
#include <android/log.h>
@@ -81,9 +82,9 @@
LogStatistics stats;
PruneList mPrune;
- // watermark for last per log id
- LogBufferElementCollection::iterator mLast[LOG_ID_MAX];
- bool mLastSet[LOG_ID_MAX];
+ // Keeps track of the iterator to the oldest log message of a given log type, as an
+ // optimization when pruning logs. Use GetOldest() to retrieve.
+ std::optional<LogBufferElementCollection::iterator> mOldest[LOG_ID_MAX];
// watermark of any worst/chatty uid processing
typedef std::unordered_map<uid_t, LogBufferElementCollection::iterator>
LogBufferIteratorMap;
@@ -181,6 +182,10 @@
bool prune(log_id_t id, unsigned long pruneRows, uid_t uid = AID_ROOT);
LogBufferElementCollection::iterator erase(
LogBufferElementCollection::iterator it, bool coalesce = false);
+
+ // Returns an iterator to the oldest element for a given log type, or mLogElements.end() if
+ // there are no logs for the given log type. Requires mLogElementsLock to be held.
+ LogBufferElementCollection::iterator GetOldest(log_id_t log_id);
};
#endif // _LOGD_LOG_BUFFER_H__