From 451c15fcb72e09afba499f188eb6e03ced49b1ca Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 28 Oct 2021 00:41:55 -0700
Subject: [PATCH] cp: attempt to work around ZFS bug

* src/copy.c (infer_scantype): Attempt a partial workaround for a
Linux file system bug (see Bug#51433).
---
 src/copy.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/copy.c b/src/copy.c
index cb9018f93..6f4566d9f 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -1097,6 +1097,16 @@ infer_scantype (int fd, struct stat const *sb,
 
 #ifdef SEEK_HOLE
   scan_inference->ext_start = lseek (fd, 0, SEEK_DATA);
+
+  /* If lseek fails with ENXIO, it may be a Linux file system bug
+     <https://bugs.gnu.org/51433>.  Try to work around it by
+     fdatasyncing the input and then retrying the lseek.  */
+  if (scan_inference->ext_start < 0 && errno == ENXIO)
+    {
+      fdatasync (fd);
+      scan_inference->ext_start = lseek (fd, 0, SEEK_DATA);
+    }
+
   if (0 <= scan_inference->ext_start)
     return LSEEK_SCANTYPE;
   else if (errno != EINVAL && !is_ENOTSUP (errno))
-- 
2.31.1