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.

diff --git a/src/basic/copy.c b/src/basic/copy.c
index 33427c6a73fb1bfbbf67b0d8ce193880c1755e84..cc5faa80a17e24a8714e0c633958067a637a4a20 100644 (file)
--- 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;
                 }