Confirm that the interface exists before calling ip

The logs are full of errors from commands such as `ip addr show` complaining
that the given interface does not exist. A Script_error exception would be
raised in such cases, which is usually caught and thrown away higher up the
stack. Still, the alarming log message is left behind, which often confuses
people.

Instead of calling out to the `ip` command and hoping for the best, we now
first check whether the interface actually exists, and raise the new
Interface_does_not_exist error if not.

Signed-off-by: Rob Hoes <[email protected]>

Author: robhoes

lib/network_utils.ml

@@ -106,6 +106,13 @@ module Sysfs = struct
     let all = Array.to_list (Sys.readdir "/sys/class/net") in
     List.filter (fun name -> Sys.is_directory ("/sys/class/net/" ^ name)) all
 
+  let exists dev =
+    List.mem dev @@ list ()
+
+  let assert_exists dev =
+    if not @@ exists dev then
+      raise (Network_error (Interface_does_not_exist dev))
+
   let list_drivers () =
     try
       Array.to_list (Sys.readdir "/sys/bus/pci/drivers")
@@ -357,6 +364,7 @@ module Ip = struct
     List.map (fun i -> List.nth args (succ i)) indices
 
   let get_link_flags dev =
+    Sysfs.assert_exists dev;
     let output = call ["link"; "show"; "dev"; dev] in
     let i = String.index output '<' in
     let j = String.index output '>' in
@@ -369,11 +377,13 @@ module Ip = struct
     with _ -> false
 
   let link_set dev args =
+    Sysfs.assert_exists dev;
     ignore (call ~log:true ("link" :: "set" :: dev :: args))
 
   let link_set_mtu dev mtu =
     try ignore (link_set dev ["mtu"; string_of_int mtu])
-    with e -> error "MTU size is not supported: %s" (string_of_int mtu)
+    with Network_error (Script_error _) ->
+      error "MTU size is not supported: %d" mtu
 
   let link_set_up dev =
     link_set dev ["up"]
@@ -390,11 +400,13 @@ module Ip = struct
       (fun () -> List.iter link_set_up up_links)
 
   let link ?(version=V46) dev attr =
+    Sysfs.assert_exists dev;
     let v = string_of_version version in
     let output = call (v @ ["link"; "show"; "dev"; dev]) in
     find output attr
 
   let addr ?(version=V46) dev attr =
+    Sysfs.assert_exists dev;
     let v = string_of_version version in
     let output = call (v @ ["addr"; "show"; "dev"; dev]) in
     find output attr
@@ -487,13 +499,15 @@ module Ip = struct
 
   let flush_ip_addr ?(ipv6=false) dev =
     try
+      Sysfs.assert_exists dev;
       let mode = if ipv6 then "-6" else "-4" in
       ignore (call ~log:true [mode; "addr"; "flush"; "dev"; dev])
     with _ -> ()
 
   let del_ip_addr dev (ip, prefixlen) = 
     let addr = Printf.sprintf "%s/%d" (Unix.string_of_inet_addr ip) prefixlen in
     try
+      Sysfs.assert_exists dev;
       ignore (call ~log:true ["addr"; "del"; addr; "dev"; dev])
     with _ -> ()
 
@@ -503,6 +517,7 @@ module Ip = struct
 
   let set_route ?network dev gateway =
     try
+      Sysfs.assert_exists dev;
       match network with
       | None ->
         ignore (call ~log:true ["route"; "replace"; "default"; "via"; Unix.string_of_inet_addr gateway; "dev"; dev])
@@ -517,12 +532,12 @@ module Ip = struct
     Printf.sprintf "%s.%d" interface vlan
 
   let create_vlan interface vlan =
-    if not (List.mem (vlan_name interface vlan) (Sysfs.list ())) then
+    if not (Sysfs.exists (vlan_name interface vlan)) then
       ignore (call ~log:true ["link"; "add"; "link"; interface; "name"; vlan_name interface vlan;
                               "type"; "vlan"; "id"; string_of_int vlan])
 
   let destroy_vlan name =
-    if List.mem name (Sysfs.list ()) then
+    if Sysfs.exists name then
       ignore (call ~log:true ["link"; "delete"; name])
 
   let set_vf_mac dev index mac =