ocaml: Unify handling of major and minor device IDs

There were 5 ad-hoc implementations, they were all getting wrong results
for the minor because only the lower 8 bits were accounted for. Use the
unixext one which handles up to 32-bit-wide minors correctly.

Signed-off-by: Pau Ruiz Safont <pau.safont@vates.tech>

Author: psafont

ocaml/tapctl/tapctl.ml

@@ -529,9 +529,9 @@ exception Not_a_device
 
 let of_device ctx path =
   let stat = Unix.stat path in
+  let module Stat = Unixext.Stat in
   if stat.Unix.st_kind <> Unix.S_BLK then raise Not_a_device ;
-  let major = stat.Unix.st_rdev / 256 in
-  let minor = stat.Unix.st_rdev mod 256 in
+  let Stat.{major; minor} = Stat.decode_st_dev stat.Unix.st_rdev in
   if driver_of_major major <> "tapdev" then raise Not_blktap ;
   match List.filter (fun (tapdev, _, _) -> tapdev.minor = minor) (list ctx) with
   | [t] ->

ocaml/vhd-tool/cli/dune

@@ -19,6 +19,7 @@
     vhd-format-lwt
     xapi-idl
     xapi-log
+    xapi-stdext-unix
     xenstore_transport.unix
     ezxenstore
   )

ocaml/vhd-tool/cli/sparse_dd.ml

@@ -213,10 +213,11 @@ let after f g =
 let find_backend_device path =
   try
     let open Ezxenstore_core.Xenstore in
+    let module Stat = Xapi_stdext_unix.Unixext.Stat in
     (* If we're looking at a xen frontend device, see if the backend
        is in the same domain. If so check if it looks like a .vhd *)
     let rdev = (Unix.LargeFile.stat path).Unix.LargeFile.st_rdev in
-    let major = rdev / 256 and minor = rdev mod 256 in
+    let Stat.{major; minor} = Stat.decode_st_dev rdev in
     let link =
       Unix.readlink (Printf.sprintf "/sys/dev/block/%d:%d/device" major minor)
     in

ocaml/vhd-tool/src/image.ml

@@ -1,11 +1,11 @@
+module Stat = Xapi_stdext_unix.Unixext.Stat
+
 let get_device_numbers path =
-  let rdev = (Unix.LargeFile.stat path).Unix.LargeFile.st_rdev in
-  let major = rdev / 256 and minor = rdev mod 256 in
-  (major, minor)
+  Unix.LargeFile.((stat path).st_rdev) |> Stat.decode_st_dev
 
 let is_nbd_device path =
   let nbd_device_num = 43 in
-  let major, _ = get_device_numbers path in
+  let Stat.{major; _} = get_device_numbers path in
   major = nbd_device_num
 
 type t = [`Vhd of string | `Raw of string | `Nbd of string * string]

ocaml/xapi/stream_vdi.ml

@@ -132,13 +132,11 @@ let write_block ~__context filename buffer ofd len =
       raise e
 
 let get_device_numbers path =
-  let rdev = (Unix.LargeFile.stat path).Unix.LargeFile.st_rdev in
-  let major = rdev / 256 and minor = rdev mod 256 in
-  (major, minor)
+  Unix.LargeFile.((stat path).st_rdev) |> Unixext.Stat.decode_st_dev
 
 let is_nbd_device path =
   let nbd_device_num = 43 in
-  let major, _ = get_device_numbers path in
+  let Unixext.Stat.{major; _} = get_device_numbers path in
   major = nbd_device_num
 
 type nbd_connect_info = {path: string; exportname: string} [@@deriving rpc]

ocaml/xapi/vhd_tool_wrapper.ml

@@ -118,10 +118,11 @@ let receive progress_cb format protocol (s : Unix.file_descr)
 let find_backend_device path =
   try
     let open Ezxenstore_core.Xenstore in
+    let module Stat = Xapi_stdext_unix.Unixext.Stat in
     (* If we're looking at a xen frontend device, see if the backend
        is in the same domain. If so check if it looks like a .vhd *)
     let rdev = (Unix.stat path).Unix.st_rdev in
-    let major = rdev / 256 and minor = rdev mod 256 in
+    let Stat.{major; minor} = Stat.decode_st_dev rdev in
     let link =
       Unix.readlink (Printf.sprintf "/sys/dev/block/%d:%d/device" major minor)
     in