eio_linux: add fallback for statx on older kernels

If statx isn't available, open the path and use fstat instead. See: io-uring: Make statx API stable https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1b6fe6e0dfecf8c82a64fb87148ad9333fa2f62e
ocaml-multicore · Sep 27, 2023 · 590df4c · 590df4c
1 parent 9256754
commit 590df4c
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Showing 2 changed files with 31 additions and 17 deletions.
diff --git a/lib_eio_linux/eio_linux.ml b/lib_eio_linux/eio_linux.ml
@@ -536,23 +536,34 @@ end = struct
     else Float.pred f
 
   let stat t ~follow path =
-    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;
-    { Eio.File.Stat.
-      dev    = X.dev x;
-      ino    = X.ino x;
-      kind   = X.kind x;
-      perm   = X.perm x;
-      nlink  = X.nlink x;
-      uid    = X.uid x;
-      gid    = X.gid x;
-      rdev   = X.rdev x;
-      size   = X.size x |> Optint.Int63.of_int64;
-      atime  = float_of_time (X.atime_sec x) (X.atime_nsec x);
-      mtime  = float_of_time (X.mtime_sec x) (X.mtime_nsec x);
-      ctime  = float_of_time (X.ctime_sec x) (X.ctime_nsec x);
-    }
+    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;
+      { Eio.File.Stat.
+        dev    = X.dev x;
+        ino    = X.ino x;
+        kind   = X.kind x;
+        perm   = X.perm x;
+        nlink  = X.nlink x;
+        uid    = X.uid x;
+        gid    = X.gid x;
+        rdev   = X.rdev x;
+        size   = X.size x |> Optint.Int63.of_int64;
+        atime  = float_of_time (X.atime_sec x) (X.atime_nsec x);
+        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

diff --git a/lib_eio_linux/sched.ml b/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