[release-branch.go1.20] Revert "internal/poll: drop redundant ENOSYS in CopyFileRange"

This reverts CL 428555.

Reason for revert: It appears that even a newer kernel can get
ENOSYS from copy_file_range.

For #58592
Fixes #58627

Change-Id: Ib8dd1be61544f54bf652a99dc0b449109f8f50ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/470316
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/internal/poll/copy_file_range_linux.go b/src/internal/poll/copy_file_range_linux.go
index 66408e459040b506a66cbab6cd6dfa5a6ac5f1a0..ba33f5145d4896cb34bfe1a14d34fba35e727669 100644 (file)
--- a/src/internal/poll/copy_file_range_linux.go
+++ b/src/internal/poll/copy_file_range_linux.go
@@ -41,18 +41,22 @@ func CopyFileRange(dst, src *FD, remain int64) (written int64, handled bool, err
                }
                n, err := copyFileRange(dst, src, int(max))
                switch err {
+               case syscall.ENOSYS:
+                       // copy_file_range(2) was introduced in Linux 4.5.
+                       // Go supports Linux >= 2.6.33, so the system call
+                       // may not be present.
+                       //
+                       // If we see ENOSYS, we have certainly not transferred
+                       // any data, so we can tell the caller that we
+                       // couldn't handle the transfer and let them fall
+                       // back to more generic code.
+                       return 0, false, nil
                case syscall.EXDEV, syscall.EINVAL, syscall.EIO, syscall.EOPNOTSUPP, syscall.EPERM:
                        // Prior to Linux 5.3, it was not possible to
-                       // copy_file_range across file systems. An attempt
-                       // to do this will result in a EXDEV error.
-                       //
-                       // Even though we have checked the kernel version and blocked
-                       // the attempts to copy_file_range(2) when the kernel version
-                       // is older than 5.3, but until now the latest kernel (5.19.x)
-                       // may still return EXDEV error in certain cases.
-                       //
-                       // If we see EXDEV, we have not transferred any data,
-                       // and we can let the caller fall back to generic code.
+                       // copy_file_range across file systems. Similarly to
+                       // the ENOSYS case above, if we see EXDEV, we have
+                       // not transferred any data, and we can let the caller
+                       // fall back to generic code.
                        //
                        // As for EINVAL, that is what we see if, for example,
                        // dst or src refer to a pipe rather than a regular