feat(exec): Add --no-session flag for improved performance

Fixes: #26588

For use cases like HPC, where `podman exec` is called in rapid succession, the standard exec process can become a bottleneck due to container locking and database I/O for session tracking.

This commit introduces a new `--no-session` flag to `podman exec`. When used, this flag invokes a new, lightweight backend implementation that:

- Skips container locking, reducing lock contention
- Bypasses the creation, tracking, and removal of exec sessions in the database
- Executes the command directly and retrieves the exit code without persisting session state
- Maintains consistency with regular exec for container lookup, TTY handling, and environment setup
- Shares implementation with health check execution to avoid code duplication

The implementation addresses all performance bottlenecks while preserving compatibility with existing exec functionality including --latest flag support and proper exit code handling.

Changes include:
- Add --no-session flag to cmd/podman/containers/exec.go
- Implement lightweight execution path in libpod/container_exec.go
- Ensure consistent container validation and environment setup
- Add comprehensive exit code testing including signal handling (exit 137)
- Optimize configuration to skip unnecessary exit command setup

Signed-off-by: Ryan McCann <ryan_mccann@student.uml.edu>
Signed-off-by: ryanmccann1024 <ryan_mccann@student.uml.edu>

test/e2e/exec_test.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	. "github.com/containers/podman/v6/test/utils"
 	. "github.com/onsi/ginkgo/v2"
@@ -616,4 +617,57 @@ RUN useradd -u 1000 auser`, fedoraMinimal)
 		Expect(session).Should(ExitCleanly())
 		Expect(session.OutputToString()).To(Equal("root"))
 	})
+
+	It("podman exec with --no-session flag", func() {
+		SkipIfRemote("The --no-session flag is not supported for remote clients")
+		session := podmanTest.RunTopContainer("no_session_test")
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(ExitCleanly())
+
+		execResult := podmanTest.Podman([]string{"exec", "--no-session", "no_session_test", "echo", "hello"})
+		execResult.WaitWithDefaultTimeout()
+		Expect(execResult).Should(ExitCleanly())
+		Expect(execResult.OutputToString()).To(Equal("hello"))
+	})
+
+	It("podman stop is not blocked by a long-running --no-session exec", func() {
+		SkipIfRemote("The --no-session flag is not supported for remote clients")
+
+		ctrName := "no_session_lock_test"
+		session := podmanTest.RunTopContainer(ctrName)
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(ExitCleanly())
+
+		execSession := podmanTest.Podman([]string{"exec", "--no-session", ctrName, "sleep", "30"})
+		stopSession := podmanTest.Podman([]string{"stop", "-t", "5", ctrName})
+		stopSession.WaitWithDefaultTimeout()
+		Expect(stopSession).Should(ExitCleanly())
+		Eventually(execSession, "5s").Should(Not(Exit(0)))
+	})
+
+	It("podman exec --no-session exit codes", func() {
+		SkipIfRemote("The --no-session flag is not supported for remote clients")
+
+		ctrName := "no_session_exit_code_test"
+		session := podmanTest.RunTopContainer(ctrName)
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(ExitCleanly())
+
+		execResult := podmanTest.Podman([]string{"exec", "--no-session", ctrName, "sh", "-c", "exit 42"})
+		execResult.WaitWithDefaultTimeout()
+		Expect(execResult).Should(ExitWithError(42, ""))
+
+		execResult = podmanTest.Podman([]string{"exec", "--no-session", ctrName, "nonexistentcommand"})
+		execResult.WaitWithDefaultTimeout()
+		Expect(execResult).Should(ExitWithError(127, "OCI runtime attempted to invoke a command that was not found"))
+
+		execSession := podmanTest.Podman([]string{"exec", "--no-session", ctrName, "sleep", "30"})
+		time.Sleep(2 * time.Second) // Give time for the first exec to start (CI is slow)
+		killSession := podmanTest.Podman([]string{"exec", ctrName, "sh", "-c", "kill -9 $(pgrep sleep)"})
+		killSession.WaitWithDefaultTimeout()
+		Expect(killSession).Should(ExitCleanly())
+
+		execSession.WaitWithDefaultTimeout()
+		Expect(execSession).Should(ExitWithError(137, ""))
+	})
 })