cpuinfo: show error when image is missing

The `criu cpuinfo check` command calls cpu_validate_cpuinfo(), which
attempts to open the cpuinfo.img file using `open_image()`. If the
image file is not found, `open_image()` returns an "empty image"
object. As a result, `cpu_validate_cpuinfo()` tries to read from it
and fails with the following error:

(00.002473) Error (criu/protobuf.c:72): Unexpected EOF on (empty-image)

This patch adds a check for an empty image and appropriate error message.

Signed-off-by: Radostin Stoyanov <[email protected]>

Author: rst0git

criu/arch/ppc64/cpu.c

@@ -64,6 +64,12 @@ int cpu_validate_cpuinfo(void)
 	if (!img)
 		return -1;
 
+	if (empty_image(img)) {
+		pr_err("No cpuinfo image\n");
+		close_image(img);
+		return -1;
+	}
+
 	if (pb_read_one(img, &cpu_info, PB_CPUINFO) < 0)
 		goto error;
 

criu/arch/s390/cpu.c

@@ -87,6 +87,12 @@ int cpu_validate_cpuinfo(void)
 	if (!img)
 		return -1;
 
+	if (empty_image(img)) {
+		pr_err("No cpuinfo image\n");
+		close_image(img);
+		return -1;
+	}
+
 	ret = 0;
 	if (pb_read_one(img, &cpu_info, PB_CPUINFO) < 0)
 		goto error;

criu/arch/x86/cpu.c

@@ -407,6 +407,12 @@ int cpu_validate_cpuinfo(void)
 	if (!img)
 		return -1;
 
+	if (empty_image(img)) {
+		pr_err("No cpuinfo image\n");
+		close_image(img);
+		return -1;
+	}
+
 	if (pb_read_one(img, &img_cpu_info, PB_CPUINFO) < 0)
 		goto err;