fixup! Unix.time_limited_{read,write}: replace select with Polly

ocaml/libs/xapi-stdext/lib/xapi-stdext-unix/unixext.ml

@@ -562,14 +562,14 @@ let with_polly_wait kind fd f =
   | S_LNK ->
       (* should never happen, the file is already open and OCaml doesn't support O_SYMLINK to open the link itself *)
       failwith "cannot read/write into a symbolic link"
-  | S_REG ->
+  | S_REG | S_BLK ->
       (* the best we can do is to split up the read/write operation into 64KiB chunks,
          and check the timeout after each chunk.
          select() would've silently succeeded here, whereas epoll() is stricted and returns EPERM
       *)
       let wait remaining_time = if remaining_time < 0. then raise Timeout in
       f wait fd
-  | S_BLK | S_CHR | S_FIFO | S_SOCK ->
+  | S_CHR | S_FIFO | S_SOCK ->
       with_polly @@ fun polly ->
       Polly.add polly fd kind ;
       let wait remaining_time =