WIP: fstat

lib_eio_posix/fs.ml

@@ -81,11 +81,6 @@ end = struct
 
   let v ~label ~path:dir_path fd = { fd; dir_path; sandbox = fd <> Fs; label; closed = false }
 
-  (* Sandboxes use [O_NOFOLLOW] when opening files ([resolve] already removed any symlinks).
-     This avoids a race where symlink might be added after [realpath] returns. *)
-  let opt_nofollow t =
-    if t.sandbox then Low_level.Open_flags.nofollow else Low_level.Open_flags.empty
-
   let open_in t ~sw path =
     let fd = Err.run (Low_level.openat ~mode:0 ~sw t.fd path) Low_level.Open_flags.rdonly in
     (Flow.of_fd fd :> Eio.File.ro_ty Eio.Resource.t)
@@ -99,7 +94,7 @@ end = struct
       | `Exclusive   perm -> perm, Low_level.Open_flags.(creat + excl)
     in
     let flags = if append then Low_level.Open_flags.(flags + append) else flags in
-    let flags = Low_level.Open_flags.(flags + rdwr + opt_nofollow t) in
+    let flags = Low_level.Open_flags.(flags + rdwr) in
     match Low_level.openat ~sw ~mode t.fd path flags with
     | fd -> (Flow.of_fd fd :> Eio.File.rw_ty r)
     | exception Unix.Unix_error (ELOOP, _, _) ->
@@ -130,12 +125,7 @@ end = struct
 
   let stat t ~follow path =
     let buf = Low_level.create_stat () in
-    if follow then (
-      Err.run (Low_level.fstatat ~buf ~follow:true) (resolve t path);
-    ) else (
-      with_parent_dir t path @@ fun dirfd path ->
-      Err.run (Low_level.fstatat ~buf ?dirfd ~follow:false) path;
-    );
+    Err.run (Low_level.fstatat ~buf ~follow t.fd) path;
     Flow.eio_of_stat buf
 
   let read_dir t path =

lib_eio_posix/low_level.ml

@@ -273,14 +273,21 @@ module Resolve = struct
     in
     aux state.dir_stack
 
-  let open_beneath_fallback ?dirfd:base ~sw:final_sw ~mode path flags =
-    Switch.run @@ fun sw ->
-    let path = parse_rel path in
+  let with_state ~sw base path fn =
     let state = { sw; path; dir_stack = Base base; max_follows = 8 } in
-    Switch.on_release sw (fun () -> close_tmp state);
+    match fn state with
+    | x -> close_tmp state; x
+    | exception ex ->
+      let bt = Printexc.get_raw_backtrace () in
+      close_tmp state;
+      Printexc.raise_with_backtrace ex bt
+
+  let open_beneath_fallback ?dirfd:base ~sw ~mode path flags =
+    let path = parse_rel path in
+    with_state ~sw base path @@ fun state ->
     let rec aux leaf =
       let base = current_base state in
-      match openat_raw ~sw:final_sw base leaf ~mode Open_flags.(flags + nofollow) with
+      match openat_raw ~sw base leaf ~mode Open_flags.(flags + nofollow) with
       | fd -> fd
       | exception (Unix.Unix_error ((ELOOP | ENOTDIR), _, _) as e)
         when state.max_follows > 0 ->
@@ -293,15 +300,21 @@ module Resolve = struct
     in
     aux (resolve state)
 
-  let with_parent ?dirfd:base path fn =
-    Switch.run @@ fun sw ->
+  let with_parent ?dirfd:base ~sw path fn =
     let path = parse_rel path in
-    let state = { sw; path; dir_stack = Base base; max_follows = 8 } in
-    Switch.on_release sw (fun () -> close_tmp state);
-    let leaf = resolve state in
-    (* todo: could close the stack sooner here *) 
-    let base = current_base state in
-    fn base leaf
+    with_state ~sw base path @@ fun state ->
+    let rec aux leaf =
+      let base = current_base state in
+      match fn base leaf with
+      | Ok x -> x
+      | Error `Symlink ->
+        state.max_follows <- state.max_follows - 1;
+        match Eio_unix.Private.read_link base leaf with
+        | target ->
+          state.path <- parse_rel target;
+          aux (resolve state)
+    in
+    aux (resolve state)
 end
 
 let open_beneath_fallback = Resolve.open_beneath_fallback       (* For tests *)
@@ -324,11 +337,12 @@ let openat ~sw ~mode fd path flags =
   | Cwd -> open_beneath ~sw ~mode ?dirfd:None path flags
   | Fd dirfd -> open_beneath ~sw ~mode ~dirfd path flags
 
-let with_parent fd path fn = (* todo: use o_resolve_beneath if available *)
+(* Note: called in worker thread *)
+let with_parent_worker ~sw fd path fn = (* todo: use o_resolve_beneath if available *)
   match fd with
   | Fs -> fn None path
-  | Cwd -> Resolve.with_parent path fn
-  | Fd dirfd -> Resolve.with_parent ~dirfd path fn
+  | Cwd -> Resolve.with_parent ~sw path (fun x y -> Ok (fn x y))
+  | Fd dirfd -> Resolve.with_parent ~sw ~dirfd path (fun x y -> Ok (fn x y))
 
 external eio_mkdirat : Unix.file_descr -> string -> Unix.file_perm -> unit = "caml_eio_posix_mkdirat"
 
@@ -357,16 +371,6 @@ external create_stat : unit -> stat = "caml_eio_posix_make_stat"
 external eio_fstatat : stat -> Unix.file_descr -> string -> int -> unit = "caml_eio_posix_fstatat"
 external eio_fstat   : stat -> Unix.file_descr -> unit = "caml_eio_posix_fstat"
 
-let fstat ~buf fd =
-  Fd.use_exn "fstat" fd @@ fun fd ->
-  eio_fstat buf fd
-
-let fstatat ~buf ?dirfd ~follow path =
-  in_worker_thread "fstat" @@ fun () ->
-  let flags = if follow then 0 else Config.at_symlink_nofollow in
-  with_dirfd "fstatat" dirfd @@ fun dirfd ->
-  eio_fstatat buf dirfd path flags
-
 external blksize : stat -> (int64 [@unboxed]) = "ocaml_eio_posix_stat_blksize_bytes" "ocaml_eio_posix_stat_blksize_native" [@@noalloc]
 external nlink   : stat -> (int64 [@unboxed]) = "ocaml_eio_posix_stat_nlink_bytes" "ocaml_eio_posix_stat_nlink_native" [@@noalloc]
 external uid     : stat -> (int64 [@unboxed]) = "ocaml_eio_posix_stat_uid_bytes" "ocaml_eio_posix_stat_uid_native" [@@noalloc]
@@ -387,6 +391,27 @@ external atime_nsec : stat -> int = "ocaml_eio_posix_stat_atime_nsec" [@@noalloc
 external ctime_nsec : stat -> int = "ocaml_eio_posix_stat_ctime_nsec" [@@noalloc]
 external mtime_nsec : stat -> int = "ocaml_eio_posix_stat_mtime_nsec" [@@noalloc]
 
+let fstat ~buf fd =
+  Fd.use_exn "fstat" fd @@ fun fd ->
+  eio_fstat buf fd
+
+let fstatat_confined ~buf ~follow dirfd path =
+  Switch.run @@ fun sw ->
+  in_worker_thread "fstat" @@ fun () ->
+  Resolve.with_parent ~sw ?dirfd path @@ fun dirfd path ->
+  with_dirfd "fstatat" dirfd @@ fun dirfd ->
+  eio_fstatat buf dirfd path Config.at_symlink_nofollow;
+  if follow && kind buf = `Symbolic_link then Error `Symlink else Ok ()
+
+let fstatat ~buf ~follow dirfd path =
+  match dirfd with
+  | Fs ->
+    in_worker_thread "fstat" @@ fun () ->
+    let flags = if follow then 0 else Config.at_symlink_nofollow in
+    eio_fstatat buf at_fdcwd path flags
+  | Cwd -> fstatat_confined ~buf ~follow None path
+  | Fd dirfd -> fstatat_confined ~buf ~follow (Some dirfd) path
+
 let lseek fd off cmd =
   Fd.use_exn "lseek" fd @@ fun fd ->
   let cmd =
@@ -496,3 +521,7 @@ module Process = struct
     | "" -> t                       (* Success! Execing the child closed [errors_w] and we got EOF. *)
     | err -> failwith err
 end
+
+let with_parent fd path fn =
+  Switch.run @@ fun sw ->
+  with_parent_worker ~sw fd path fn

lib_eio_posix/low_level.mli

@@ -49,7 +49,7 @@ type stat
 val create_stat : unit -> stat
 
 val fstat : buf:stat -> fd -> unit
-val fstatat : buf:stat -> ?dirfd:fd -> follow:bool -> string -> unit
+val fstatat : buf:stat -> follow:bool -> dir_fd -> string -> unit
 
 external blksize : stat -> (int64 [@unboxed]) = "ocaml_eio_posix_stat_blksize_bytes" "ocaml_eio_posix_stat_blksize_native" [@@noalloc]
 external nlink   : stat -> (int64 [@unboxed]) = "ocaml_eio_posix_stat_nlink_bytes" "ocaml_eio_posix_stat_nlink_native" [@@noalloc]

lib_eio_posix/net.ml

@@ -109,7 +109,7 @@ let listen ~reuse_addr ~reuse_port ~backlog ~sw (listen_addr : Eio.Net.Sockaddr.
     | `Unix path         ->
       if reuse_addr then (
         let buf = Low_level.create_stat () in
-        match Low_level.fstatat ~buf ~follow:false path with
+        match Low_level.fstatat ~buf ~follow:false Fs path with
         | () -> if Low_level.kind buf = `Socket then Unix.unlink path
         | exception Unix.Unix_error (Unix.ENOENT, _, _) -> ()
         | exception Unix.Unix_error (code, name, arg) -> raise @@ Err.wrap code name arg