Merge pull request #624 from talex5/statx-fallback

eio_linux: add fallback for statx on older kernels

lib_eio/path.ml

@@ -69,6 +69,16 @@ let stat ~follow t =
     let bt = Printexc.get_raw_backtrace () in
     Exn.reraise_with_context ex bt "examining %a" pp t
 
+let kind ~follow t =
+  try ((stat ~follow t).kind :> [File.Stat.kind | `Not_found])
+  with Exn.Io (Fs.E Not_found _, _) -> `Not_found
+
+let is_file t =
+  kind ~follow:true t = `Regular_file
+
+let is_directory t = 
+  kind ~follow:true t = `Directory
+
 let with_open_in path fn =
   Switch.run @@ fun sw -> fn (open_in ~sw path)
 

lib_eio/path.mli

@@ -128,7 +128,7 @@ val read_dir : _ t -> string list
 
     Note: The special Unix entries "." and ".." are not included in the results. *)
 
-(** {2 Metadata} *)
+(** {1 Metadata} *)
 
 val stat : follow:bool -> _ t -> File.Stat.t
 (** [stat ~follow t] returns metadata about the file [t].
@@ -136,6 +136,21 @@ val stat : follow:bool -> _ t -> File.Stat.t
     If [t] is a symlink, the information returned is about the target if [follow = true],
     otherwise it is about the link itself. *)
 
+val kind : follow:bool -> _ t -> [ File.Stat.kind | `Not_found ]
+(** [kind ~follow t] is the type of [t], or [`Not_found] if it doesn't exist.
+
+    @param follow If [true] and [t] is a symlink, return the type of the target rather than [`Symbolic_link]. *)
+
+val is_file : _ t -> bool
+(** [is_file t] is [true] if [t] is a regular file, and [false] if it doesn't exist or has a different type.
+
+    [is_file t] is [kind ~follow:true t = `Regular_file]. *)
+
+val is_directory : _ t -> bool
+(** [is_directory t] is [true] if [t] is a directory, and [false] if it doesn't exist or has a different type.
+
+    [is_directory t] is [kind ~follow:true t = `Directory]. *)
+
 (** {1 Other} *)
 
 val unlink : _ t -> unit

lib_eio_linux/eio_linux.ml

@@ -536,6 +536,7 @@ end = struct
     else Float.pred f
 
   let stat t ~follow path =
+    if !Sched.statx_works then (
       let module X = Uring.Statx in
       let x = X.create () in
       Low_level.statx_confined ~follow ~mask:X.Mask.basic_stats t.fd path x;
@@ -553,6 +554,16 @@ end = struct
         mtime  = float_of_time (X.mtime_sec x) (X.mtime_nsec x);
         ctime  = float_of_time (X.ctime_sec x) (X.ctime_nsec x);
       }
+    ) else (
+      (* Linux < 5.18 *)
+      Switch.run @@ fun sw ->
+      let fd = Low_level.openat ~sw ~seekable:false t.fd (if path = "" then "." else path)
+          ~access:`R
+          ~flags:Uring.Open_flags.(cloexec + path + (if follow then empty else nofollow))
+          ~perm:0
+      in
+      Flow.stat fd
+    )
 
   let rename t old_path t2 new_path =
     match get_dir_fd_opt t2 with

lib_eio_linux/sched.ml

@@ -11,6 +11,8 @@ module Lf_queue = Eio_utils.Lf_queue
 
 let system_thread = Ctf.mint_id ()
 
+let statx_works = ref false     (* Before Linux 5.18, statx is unreliable *)
+
 type exit = [`Exit_scheduler]
 
 type file_offset = [
@@ -526,6 +528,7 @@ let with_sched ?(fallback=no_fallback) config fn =
       Uring.exit uring;
       fallback (`Msg "Linux >= 5.11 is required for io_uring support")
     ) else (
+      statx_works := Uring.op_supported probe Uring.Op.msg_ring;
       match
         let mem =
           let fixed_buf_len = block_size * n_blocks in

tests/fs.md

@@ -59,10 +59,6 @@ let try_rmdir path =
 let chdir path =
   traceln "chdir %S" path;
   Unix.chdir path
-
-let assert_kind path kind =
-  Path.with_open_in path @@ fun file ->
-  assert ((Eio.File.stat file).kind = kind)
 ```
 
 # Basic test cases
@@ -224,7 +220,9 @@ You can remove a file using unlink:
   Path.save ~create:(`Exclusive 0o600) (cwd / "subdir/file2") "data2";
   try_read_file (cwd / "file");
   try_read_file (cwd / "subdir/file2");
+  assert (Eio.Path.kind ~follow:true (cwd / "file") = `Regular_file);
   try_unlink (cwd / "file");
+  assert (Eio.Path.kind ~follow:true (cwd / "file") = `Not_found);
   try_unlink (cwd / "subdir/file2");
   try_read_file (cwd / "file");
   try_read_file (cwd / "subdir/file2");
@@ -541,9 +539,9 @@ let try_stat path =
   let cwd = Eio.Stdenv.cwd env in
   Switch.run @@ fun sw ->
   try_mkdir (cwd / "stat_subdir");
-  assert_kind (cwd / "stat_subdir") `Directory;
+  assert (Eio.Path.is_directory (cwd / "stat_subdir"));
   try_write_file (cwd / "stat_reg") "kingbula" ~create:(`Exclusive 0o600);
-  assert_kind (cwd / "stat_reg") `Regular_file;;
+  assert (Eio.Path.is_file (cwd / "stat_reg"));
 +mkdir <cwd:stat_subdir> -> ok
 +write <cwd:stat_reg> -> ok
 - : unit = ()
@@ -565,6 +563,7 @@ Fstatat:
   try_stat (cwd / "..");
   Unix.symlink ".." "parent-symlink";
   try_stat (cwd / "parent-symlink");
+  try_stat (cwd / "missing1" / "missing2");
 +mkdir <cwd:stat_subdir2> -> ok
 +<cwd:stat_subdir2> -> directory
 +<cwd:symlink> -> symbolic link / directory
@@ -572,6 +571,7 @@ Fstatat:
 +<cwd> -> directory
 +<cwd:..> -> Fs Permission_denied _
 +<cwd:parent-symlink> -> symbolic link / Fs Permission_denied _
++<cwd:missing1/missing2> -> Fs Not_found _
 - : unit = ()
 ```