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CP-53314: Read and watch <domain>/data/service in xenstore to DB #6317

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Mar 4, 2025
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CP-53314: Read and watch <domain>/data/service in xenstore to DB #6317

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CP-53314: Read and watch <domain>/data/service in xenstore to DB
changlei-li Feb 19, 2025
a6b5b7c
Fix review comments and add unit test for guest_agent
changlei-li Feb 26, 2025
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27 changes: 26 additions & 1 deletion ocaml/xapi/xapi_guest_agent.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,31 @@ let dead_domains : IntSet.t ref = ref IntSet.empty

let mutex = Mutex.create ()

(* Parse data/service which has the following structure:
data/service/<service_name>/<key> = <value>
data/service/<service_name>/<key> = <value>
...
data/service/<service_name>/<key> = <value>
Read and convert to [(<service_name>/<key>, <value>)] pair list.
The list is intended to store in VM_guest_metrics.services at last *)
let get_guest_services (lookup : string -> string option)
(list : string -> string list) =
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What is the list function doing?

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list is defined in xapi_xenops.ml update_vm. It lists all subdirs and keys in one depth under the given dir. In its definition, the data source is a big string string map like [("a", ""); ("a/b", ""); ("a/b/k1", "v1"); ("a/b/k2", "v2"); ("a/c/k1", "v1"); ("a/c/k2", "v2")]. Then function list "a" will give all subdirs ["b", "c"]. It needs to be noticed that the data source is not exposed to the caller in xapi_guest_agent.ml

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utop # list_subkeys ["aaa/bbb/c", "x"] "aaa/bb";;
- : string list = ["b"]

Is this correct?

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It's incorrect. I believe the real implementation of list in xapi_xenops.ml update_vm has this problem, too. Normally, it's a internal function and the caller only pass the parameter as a intact dir, so the problem is not exposed. It deserves to rasie a ticket to fix it.

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  let ls assoc path =
    let split = String.split_on_char '/' in
    let prefix = split path in
    let paths = List.map (fun (path, _) -> split path) assoc in
    let rec entry prefix path =
      match prefix, path with
      | [], x::_ -> Some x
      | x::xs, y::ys when x = y -> entry xs ys
      | _ -> None
    in
      List.filter_map (entry prefix) paths

let base_path = "data/service" in
let services = list base_path in
List.fold_left
(fun acc service ->
let sub_path = base_path // service in
List.fold_left
(fun acc key ->
let full_path_key = sub_path // key in
let db_key = service // key in
let value = lookup full_path_key in
(db_key, Option.value ~default:"" value) :: acc
)
acc (list sub_path)
)
[] services

(* In the following functions, 'lookup' reads a key from xenstore and 'list' reads
a directory from xenstore. Both are relative to the guest's domainpath. *)
let get_initial_guest_metrics (lookup : string -> string option)
Expand Down Expand Up @@ -290,7 +315,7 @@ let get_initial_guest_metrics (lookup : string -> string option)
; networks "xenserver/attr" "net-sriov-vf" list
]
)
and services = []
and services = get_guest_services lookup list
and other = List.append (to_map (other all_control)) ts
and memory = to_map memory
and last_updated = Unix.gettimeofday () in
Expand Down
2 changes: 2 additions & 0 deletions ocaml/xenopsd/xc/xenops_server_xen.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -2849,6 +2849,7 @@ module VM = struct
; ("drivers", None, 0)
; ("data", None, 0)
(* in particular avoid data/volumes which contains many entries for each disk *)
; ("data/service", None, 1) (* data/service/<service-name>/<key>*)
]
|> List.fold_left
(fun acc (dir, excludes, depth) ->
Expand Down Expand Up @@ -4825,6 +4826,7 @@ module Actions = struct
sprintf "/local/domain/%d/attr" domid
; sprintf "/local/domain/%d/data/updated" domid
; sprintf "/local/domain/%d/data/ts" domid
; sprintf "/local/domain/%d/data/service" domid
; sprintf "/local/domain/%d/memory/target" domid
; sprintf "/local/domain/%d/memory/uncooperative" domid
; sprintf "/local/domain/%d/console/vnc-port" domid
Expand Down