internal/poll: improve Splice comments

Clarify the behavior of splice on older kernels, merge comments so
control flow becomes more obvious, as discussed in CL 133575.

Change-Id: I95855991bd0b1fa1c78a900b39c4382f65d83468
Reviewed-on: https://go-review.googlesource.com/135436
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/internal/poll/splice_linux.go b/src/internal/poll/splice_linux.go
index 9ba94d648b6846ada887d0aff3688b6c075531fd..4f97298417c3df6c623a5a3cbc0faf31faf1b152 100644 (file)
--- a/src/internal/poll/splice_linux.go
+++ b/src/internal/poll/splice_linux.go
@@ -39,15 +39,18 @@ func Splice(dst, src *FD, remain int64) (written int64, handled bool, sc string,
                        max = int(remain)
                }
                inPipe, err = spliceDrain(pwfd, src, max)
-               // the operation is considered handled if splice returns no error, or
-               // an error other than EINVAL. An EINVAL means the kernel does not
-               // support splice for the socket type of dst and/or src. The failed
-               // syscall does not consume any data so it is safe to fall back to a
-               // generic copy.
-               handled = handled || (err != syscall.EINVAL)
+               // The operation is considered handled if splice returns no
+               // error, or an error other than EINVAL. An EINVAL means the
+               // kernel does not support splice for the socket type of src.
+               // The failed syscall does not consume any data so it is safe
+               // to fall back to a generic copy.
+               //
                // spliceDrain should never return EAGAIN, so if err != nil,
-               // Splice cannot continue. If inPipe == 0 && err == nil,
-               // src is at EOF, and the transfer is complete.
+               // Splice cannot continue.
+               //
+               // If inPipe == 0 && err == nil, src is at EOF, and the
+               // transfer is complete.
+               handled = handled || (err != syscall.EINVAL)
                if err != nil || (inPipe == 0 && err == nil) {
                        break
                }