mymalloc: use ftruncate(2) when creating a sparse file

Unlike pwrite(2), it won't dirty the last page, and it's fewer
arguments so argument passing is simpler.

1 files changed, 2 insertions, 2 deletions

diff --git a/mymalloc.h b/mymalloc.h
index e781b43..eda669f 100644
--- a/mymalloc.h
+++ b/mymalloc.h
@@ -69,9 +69,9 @@ static void *my_mmap(size_t size)
         if (fd < 0) {
                 flags |= MAP_ANONYMOUS;
         } else {
-                ssize_t w = pwrite(fd, "", 1, size - 1); /* sparse file */
+                int t = ftruncate(fd, size); /* sparse file */
 
-                if (w <= 0) { /* 0 may be ENOSPC */
+                if (t < 0) {
                         flags |= MAP_ANONYMOUS;
                         close(fd);
                         fd = -1;