libbb/copyfd.c: don't mmap a largish buffer if we only want to copy a few kb

function                                             old     new   delta
bb_full_fd_action                                    283     295     +12

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/libbb/copyfd.c b/libbb/copyfd.c
index c5f8b5b87..f42eb7623 100644
--- a/libbb/copyfd.c
+++ b/libbb/copyfd.c
@@ -22,6 +22,8 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
         char *buffer;
         int buffer_size;
 
+        if (size > 0 && size <= 4 * 1024)
+                goto use_small_buf;
         /* We want page-aligned buffer, just in case kernel is clever
          * and can do page-aligned io more efficiently */
         buffer = mmap(NULL, CONFIG_FEATURE_COPYBUF_KB * 1024,
@@ -30,6 +32,7 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
                         /* ignored: */ -1, 0);
         buffer_size = CONFIG_FEATURE_COPYBUF_KB * 1024;
         if (buffer == MAP_FAILED) {
+ use_small_buf:
                 buffer = alloca(4 * 1024);
                 buffer_size = 4 * 1024;
         }