[Libguestfs] [PATCH supermin 1/9] kernel: Refactor code for locating the kernel.

[Richard W.M. Jones]

Refactor the code for locating the kernel into separate functions,
making clear the purpose of each part of the code.

This is pure refactoring and doesn't change the meaning of the code.
---
 src/format_ext2_kernel.ml | 126 ++++++++++++++++++++++++++--------------------
 1 file changed, 72 insertions(+), 54 deletions(-)

diff --git a/src/format_ext2_kernel.ml b/src/format_ext2_kernel.ml
index 5d1ae66..a12fbd2 100644
--- a/src/format_ext2_kernel.ml
+++ b/src/format_ext2_kernel.ml
@@ -40,49 +40,21 @@ let patt_of_cpu host_cpu =
   List.map (fun model -> sprintf "vmlinu?-*-%s" model) models
 
 let rec build_kernel debug host_cpu copy_kernel kernel =
-  (* Locate the kernel. *)
+  (* Locate the kernel.
+   * SUPERMIN_* environment variables override everything.  If those
+   * are not present then we look in /lib/modules and /boot.
+   *)
   let kernel_file, kernel_name, kernel_version, modpath =
-    try
-      let kernel_env = getenv "SUPERMIN_KERNEL" in
-      if debug >= 1 then
-        printf "supermin: kernel: SUPERMIN_KERNEL environment variable %s\n%!"
-          kernel_env;
-      let kernel_version =
-        try
-          let v = getenv "SUPERMIN_KERNEL_VERSION" in
-          if debug >= 1 then
-            printf "supermin: kernel: SUPERMIN_KERNEL_VERSION environment variable %s\n%!" v;
-          v
-        with Not_found -> get_kernel_version_from_file kernel_env in
-      if debug >= 1 then
-        printf "supermin: kernel: SUPERMIN_KERNEL version %s\n%!"
-          kernel_version;
-      let kernel_name = Filename.basename kernel_env in
-      let modpath = find_modpath debug kernel_version in
-      kernel_env, kernel_name, kernel_version, modpath
-    with Not_found ->
-      let kernels =
-        let files = glob "/lib/modules/*/vmlinuz" [GLOB_NOSORT; GLOB_NOESCAPE] in
-        let files = Array.to_list files in
-        let kernels =
-          List.map (
-            fun f ->
-              let modpath = Filename.dirname f in
-              f, Filename.basename f, Filename.basename modpath, modpath
-          ) files in
-        List.sort (
-          fun (_, _, a, _) (_, _, b, _) -> compare_version b a
-        ) kernels in
-
-      if kernels <> [] then (
-        let kernel = List.hd kernels in
-        if debug >= 1 then (
-          let kernel_file, _, _, _ = kernel in
-          printf "supermin: kernel: picked vmlinuz %s\n%!" kernel_file;
-        );
-        kernel
-      ) else
-        find_kernel debug host_cpu kernel in
+    match find_kernel_from_env_vars debug with
+    | Some k -> k
+    | None ->
+       match find_kernel_from_lib_modules debug with
+       | Some k -> k
+       | None ->
+          match find_kernel_from_boot debug host_cpu with
+          | Some k -> k
+          | None ->
+             error_no_kernels host_cpu in
 
   if debug >= 1 then (
     printf "supermin: kernel: kernel_version %s\n" kernel_version;
@@ -93,7 +65,52 @@ let rec build_kernel debug host_cpu copy_kernel kernel =
 
   (kernel_version, modpath)
 
-and find_kernel debug host_cpu kernel =
+and find_kernel_from_env_vars debug  =
+  try
+    let kernel_env = getenv "SUPERMIN_KERNEL" in
+    if debug >= 1 then
+      printf "supermin: kernel: SUPERMIN_KERNEL environment variable %s\n%!"
+             kernel_env;
+    let kernel_version =
+      try
+        let v = getenv "SUPERMIN_KERNEL_VERSION" in
+        if debug >= 1 then
+          printf "supermin: kernel: SUPERMIN_KERNEL_VERSION environment variable %s\n%!" v;
+        v
+      with Not_found -> get_kernel_version_from_file kernel_env in
+    if debug >= 1 then
+      printf "supermin: kernel: SUPERMIN_KERNEL version %s\n%!"
+             kernel_version;
+    let kernel_name = Filename.basename kernel_env in
+    let modpath = find_modpath debug kernel_version in
+    Some (kernel_env, kernel_name, kernel_version, modpath)
+  with Not_found -> None
+
+and find_kernel_from_lib_modules debug =
+  let kernels =
+    let files = glob "/lib/modules/*/vmlinuz" [GLOB_NOSORT; GLOB_NOESCAPE] in
+    let files = Array.to_list files in
+    let kernels =
+      List.map (
+        fun f ->
+          let modpath = Filename.dirname f in
+          f, Filename.basename f, Filename.basename modpath, modpath
+      ) files in
+    List.sort (
+      fun (_, _, a, _) (_, _, b, _) -> compare_version b a
+    ) kernels in
+
+  if kernels <> [] then (
+    let kernel = List.hd kernels in
+    if debug >= 1 then (
+      let kernel_file, _, _, _ = kernel in
+      printf "supermin: kernel: picked vmlinuz %s\n%!" kernel_file;
+    );
+    Some kernel
+  ) else
+    None
+
+and find_kernel_from_boot debug host_cpu =
   let is_arm =
     String.length host_cpu >= 3 &&
     host_cpu.[0] = 'a' && host_cpu.[1] = 'r' && host_cpu.[2] = 'm' in
@@ -111,19 +128,20 @@ and find_kernel debug host_cpu kernel =
       (* In original: ls -1dvr /boot/vmlinuz-* 2>/dev/null | grep -v xen *)
       kernel_filter ["vmlinu?-*"] is_arm all_files in
 
-  if files = [] then no_kernels host_cpu;
-
-  let files = List.sort (fun a b -> compare_version b a) files in
-  let kernel_name = List.hd files in
-  let kernel_version = get_kernel_version kernel_name in
+  if files = [] then None
+  else (
+    let files = List.sort (fun a b -> compare_version b a) files in
+    let kernel_name = List.hd files in
+    let kernel_version = get_kernel_version kernel_name in
 
-  if debug >= 1 then
-    printf "supermin: kernel: picked kernel %s\n%!" kernel_name;
+    if debug >= 1 then
+      printf "supermin: kernel: picked kernel %s\n%!" kernel_name;
 
-  (* Get the kernel modules. *)
-  let modpath = find_modpath debug kernel_version in
+    (* Get the kernel modules. *)
+    let modpath = find_modpath debug kernel_version in
 
-  ("/boot" // kernel_name), kernel_name, kernel_version, modpath
+    Some (("/boot" // kernel_name), kernel_name, kernel_version, modpath)
+  )
 
 and kernel_filter patterns is_arm all_files =
   let files =
@@ -143,7 +161,7 @@ and kernel_filter patterns is_arm all_files =
     ) in
   List.filter (fun filename -> has_modpath filename) files
 
-and no_kernels host_cpu =
+and error_no_kernels host_cpu =
   error "\
 failed to find a suitable kernel (host_cpu=%s).
 
-- 
2.13.1