From c674b3dd83d1a9cb30ed235bc4302a7388e011e4 Mon Sep 17 00:00:00 2001
From: Paul Holzinger <pholzing@redhat.com>
Date: Wed, 4 Jan 2023 17:46:50 +0100
Subject: [PATCH] journald: seek to time when --since is used

Instead of reading the full journal which can be expensive we can seek
based on the time.

If you have a journald with many podman events just compare the time
`time podman events --since 1s --stream=false` with and without this
patch.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>
---
 libpod/container_log_linux.go  | 11 +++++++++--
 libpod/events/journal_linux.go |  9 +++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/libpod/container_log_linux.go b/libpod/container_log_linux.go
index e8f957322b..ccc05d42d0 100644
--- a/libpod/container_log_linux.go
+++ b/libpod/container_log_linux.go
@@ -80,8 +80,15 @@ func (c *Container) readFromJournal(ctx context.Context, options *logs.LogOption
 		return fmt.Errorf("adding filter to journald logger: %v: %w", match, err)
 	}
 
-	if err := journal.SeekHead(); err != nil {
-		return err
+	if options.Since.IsZero() {
+		if err := journal.SeekHead(); err != nil {
+			return err
+		}
+	} else {
+		// seek based on time which helps to reduce unnecessary event reads
+		if err := journal.SeekRealtimeUsec(uint64(options.Since.UnixMicro())); err != nil {
+			return err
+		}
 	}
 	// API requires Next() immediately after SeekHead().
 	if _, err := journal.Next(); err != nil {
diff --git a/libpod/events/journal_linux.go b/libpod/events/journal_linux.go
index da2156c2c8..9c8b9cae11 100644
--- a/libpod/events/journal_linux.go
+++ b/libpod/events/journal_linux.go
@@ -121,6 +121,15 @@ func (e EventJournalD) Read(ctx context.Context, options ReadOptions) error {
 		if _, err := j.Previous(); err != nil {
 			return fmt.Errorf("failed to move journal cursor to previous entry: %w", err)
 		}
+	} else if len(options.Since) > 0 {
+		since, err := util.ParseInputTime(options.Since, true)
+		if err != nil {
+			return err
+		}
+		// seek based on time which helps to reduce unnecessary event reads
+		if err := j.SeekRealtimeUsec(uint64(since.UnixMicro())); err != nil {
+			return err
+		}
 	}
 
 	for {