copy: add splice() based fallback

Apparently, sendfile() does not work between fifos and ttys, but
splice() does, hence let's optionally fall back to that. This is useful
to implement the fallback pager this way.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/basic/copy.c b/src/basic/copy.c
index 33427c6a73..cc5faa80a1 100644
--- a/src/basic/copy.c
+++ b/src/basic/copy.c
@@ -30,7 +30,7 @@
 #define COPY_BUFFER_SIZE (16*1024)
 
 int copy_bytes(int fdf, int fdt, off_t max_bytes, bool try_reflink) {
-        bool try_sendfile = true;
+        bool try_sendfile = true, try_splice = true;
         int r;
 
         assert(fdf >= 0);
@@ -69,7 +69,23 @@ int copy_bytes(int fdf, int fdt, off_t max_bytes, bool try_reflink) {
                         } else if (n == 0) /* EOF */
                                 break;
                         else if (n > 0)
-                                /* Succcess! */
+                                /* Success! */
+                                goto next;
+                }
+
+                /* The try splice, unless we already tried */
+                if (try_splice) {
+                        n  = splice(fdf, NULL, fdt, NULL, m, 0);
+                        if (n < 0) {
+                                if (errno != EINVAL && errno != ENOSYS)
+                                        return -errno;
+
+                                try_splice = false;
+                                /* use fallback below */
+                        } else if (n == 0) /* EOF */
+                                break;
+                        else if (n > 0)
+                                /* Success! */
                                 goto next;
                 }