engine: add platform field to EngineConfig

docs/containers.conf.5.md

@@ -807,6 +807,14 @@ Locks are recycled and can be reused after the associated container, pod, or vol
 The default number available is 2048.
 If this is changed, a lock renumbering must be performed, using the `podman system renumber` command.
 
+**platform**=""
+
+Specifies the default platform for image operations such as pull, build, run,
+and create. When set, container engines will use this platform instead of the
+host's native platform. The format is `os/arch` or `os/arch/variant` (e.g.,
+`linux/amd64`, `linux/arm64/v8`). If empty (the default), the host's platform
+is used.
+
 **pod_exit_policy**="continue"
 
 Set the exit policy of the pod when the last container exits.  Supported policies are:

pkg/config/config.go

@@ -423,6 +423,12 @@ type EngineConfig struct {
 	// OCIRuntimes are the set of configured OCI runtimes (default is runc).
 	OCIRuntimes map[string][]string `toml:"runtimes,omitempty"`
 
+	// Platform specifies the default platform (os/arch[/variant]) for image
+	// operations such as pull, build, run, and create. If empty, the host's
+	// platform is used. Format: "os/arch" or "os/arch/variant" (e.g.,
+	// "linux/amd64", "linux/arm64/v8").
+	Platform string `toml:"platform,omitempty"`
+
 	// PlatformToOCIRuntime requests specific OCI runtime for a specified platform of image.
 	PlatformToOCIRuntime map[string]string `toml:"platform_to_oci_runtime,omitempty"`
 
@@ -731,6 +737,40 @@ func (c *EngineConfig) ImagePlatformToRuntime(os string, arch string) string {
 	return c.OCIRuntime
 }
 
+// PlatformComponents parses the Platform field and returns the individual
+// os, architecture, and variant components. Empty strings are returned for
+// unset components. If Platform is empty, all returned values are empty.
+func (c *EngineConfig) PlatformComponents() (os, arch, variant string) {
+	if c.Platform == "" {
+		return "", "", ""
+	}
+	parts := strings.SplitN(c.Platform, "/", 3)
+	switch len(parts) {
+	case 3:
+		return parts[0], parts[1], parts[2]
+	case 2:
+		return parts[0], parts[1], ""
+	default:
+		return parts[0], "", ""
+	}
+}
+
+// validatePlatform checks that the Platform field, if set, is a valid
+// os/arch or os/arch/variant string.
+func (c *EngineConfig) validatePlatform() error {
+	if c.Platform == "" {
+		return nil
+	}
+	parts := strings.SplitN(c.Platform, "/", 3)
+	if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
+		return fmt.Errorf("invalid platform %q: must be in the format os/arch[/variant]", c.Platform)
+	}
+	if len(parts) == 3 && parts[2] == "" {
+		return fmt.Errorf("invalid platform %q: variant must not be empty when specified", c.Platform)
+	}
+	return nil
+}
+
 // CheckCgroupsAndAdjustConfig checks if we're running rootless with the systemd
 // cgroup manager. In case the user session isn't available, we're switching the
 // cgroup manager to cgroupfs.  Note, this only applies to rootless.
@@ -845,6 +885,10 @@ func (c *EngineConfig) Validate() error {
 		return err
 	}
 
+	if err := c.validatePlatform(); err != nil {
+		return err
+	}
+
 	if err := ValidateImageVolumeMode(c.ImageVolumeMode); err != nil {
 		return err
 	}

pkg/config/config_test.go

@@ -326,6 +326,7 @@ image_copy_tmp_dir="storage"`
 			gomega.Expect(defaultConfig.Network.NetavarkPluginDirs.Get()).To(gomega.Equal([]string{"/usr/netavark"}))
 			gomega.Expect(defaultConfig.Engine.NumLocks).To(gomega.BeEquivalentTo(2048))
 			gomega.Expect(defaultConfig.Engine.OCIRuntimes).To(gomega.Equal(OCIRuntimeMap))
+			gomega.Expect(defaultConfig.Engine.Platform).To(gomega.BeEmpty())
 			gomega.Expect(defaultConfig.Engine.PlatformToOCIRuntime).To(gomega.Equal(PlatformToOCIRuntimeMap))
 			gomega.Expect(defaultConfig.Containers.HTTPProxy).To(gomega.BeFalse())
 			gomega.Expect(defaultConfig.Engine.NetworkCmdOptions.Get()).To(gomega.BeEmpty())
@@ -528,6 +529,7 @@ image_copy_tmp_dir="storage"`
 			gomega.Expect(config.Containers.Privileged).To(gomega.BeTrue())
 			gomega.Expect(config.Containers.ReadOnly).To(gomega.BeTrue())
 			gomega.Expect(config.Engine.ImageParallelCopies).To(gomega.Equal(uint(10)))
+			gomega.Expect(config.Engine.Platform).To(gomega.Equal("linux/amd64"))
 			gomega.Expect(config.Engine.PlatformToOCIRuntime).To(gomega.Equal(PlatformToOCIRuntimeMap))
 			gomega.Expect(config.Engine.ImageDefaultFormat).To(gomega.Equal("v2s2"))
 			gomega.Expect(config.Engine.CompressionFormat).To(gomega.BeEquivalentTo("zstd:chunked"))
@@ -661,6 +663,68 @@ image_copy_tmp_dir="storage"`
 			err = defConf.Engine.Validate()
 			gomega.Expect(err).To(gomega.HaveOccurred())
 		})
+
+		It("should succeed with valid platform", func() {
+			defConf, err := defaultConfig()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "linux/amd64"
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "linux/arm64/v8"
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		})
+
+		It("should succeed with empty platform", func() {
+			defConf, err := defaultConfig()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = ""
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		})
+
+		It("should fail with invalid platform", func() {
+			defConf, err := defaultConfig()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "linux"
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).To(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "linux/amd64/"
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).To(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "/amd64"
+			err = defConf.Engine.Validate()
+			gomega.Expect(err).To(gomega.HaveOccurred())
+		})
+
+		It("should parse platform components correctly", func() {
+			defConf, err := defaultConfig()
+			gomega.Expect(err).ToNot(gomega.HaveOccurred())
+
+			defConf.Engine.Platform = "linux/amd64"
+			os, arch, variant := defConf.Engine.PlatformComponents()
+			gomega.Expect(os).To(gomega.Equal("linux"))
+			gomega.Expect(arch).To(gomega.Equal("amd64"))
+			gomega.Expect(variant).To(gomega.Equal(""))
+
+			defConf.Engine.Platform = "linux/arm64/v8"
+			os, arch, variant = defConf.Engine.PlatformComponents()
+			gomega.Expect(os).To(gomega.Equal("linux"))
+			gomega.Expect(arch).To(gomega.Equal("arm64"))
+			gomega.Expect(variant).To(gomega.Equal("v8"))
+
+			defConf.Engine.Platform = ""
+			os, arch, variant = defConf.Engine.PlatformComponents()
+			gomega.Expect(os).To(gomega.Equal(""))
+			gomega.Expect(arch).To(gomega.Equal(""))
+			gomega.Expect(variant).To(gomega.Equal(""))
+		})
 	})
 
 	Describe("Service Destinations", func() {

pkg/config/testdata/containers_override.conf

@@ -18,6 +18,7 @@ events_container_create_inspect_data = true
 pod_exit_policy="stop"
 compression_format="zstd:chunked"
 cdi_spec_dirs = [ "/somepath" ]
+platform = "linux/amd64"
 
 [engine.platform_to_oci_runtime]
 hello = "world"