logs: support --tail 0

change the default to -1, so that we can change the semantic of
"--tail 0" to not print any existing log line.

Closes: https://github.com/containers/libpod/issues/4396

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/test/e2e/logs_test.go b/test/e2e/logs_test.go
index f34d85d76..e25364695 100644
--- a/test/e2e/logs_test.go
+++ b/test/e2e/logs_test.go
@@ -57,6 +57,18 @@ var _ = Describe("Podman logs", func() {
 		Expect(len(results.OutputToStringArray())).To(Equal(2))
 	})
 
+	It("podman logs tail zero lines", func() {
+		logc := podmanTest.Podman([]string{"run", "-dt", ALPINE, "sh", "-c", "echo podman; echo podman; echo podman"})
+		logc.WaitWithDefaultTimeout()
+		Expect(logc.ExitCode()).To(Equal(0))
+		cid := logc.OutputToString()
+
+		results := podmanTest.Podman([]string{"logs", "--tail", "0", cid})
+		results.WaitWithDefaultTimeout()
+		Expect(results.ExitCode()).To(Equal(0))
+		Expect(len(results.OutputToStringArray())).To(Equal(0))
+	})
+
 	It("podman logs tail 99 lines", func() {
 		logc := podmanTest.Podman([]string{"run", "-dt", ALPINE, "sh", "-c", "echo podman; echo podman; echo podman"})
 		logc.WaitWithDefaultTimeout()