copy: add brief comment to copy_bytes() explaining its return values

diff --git a/src/basic/copy.c b/src/basic/copy.c
index ff53f8394d1f8fbdb434fe6aebb1af84565d234b..673272d654aaf7b261e26fb512281e80ecabe3bb 100644 (file)
--- a/src/basic/copy.c
+++ b/src/basic/copy.c
@@ -65,6 +65,10 @@ int copy_bytes(int fdf, int fdt, uint64_t max_bytes, CopyFlags copy_flags) {
         assert(fdf >= 0);
         assert(fdt >= 0);
 
+        /* Tries to copy bytes from the file descriptor 'fdf' to 'fdt' in the smartest possible way. Copies a maximum
+         * of 'max_bytes', which may be specified as UINT64_MAX, in which no maximum is applied. Returns negative on
+         * error, zero if EOF is hit before the bytes limit is hit and positive otherwise. */
+
 #if 0 /// UNNEEDED by elogind
         /* Try btrfs reflinks first. */
         if ((copy_flags & COPY_REFLINK) &&