fix posix_fadvise() error handling

src/os/unix/ngx_files.c

diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index 2264cc1..0ef0838 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -402,6 +402,26 @@
 }
 
 
+#if (NGX_HAVE_POSIX_FADVISE)
+
+ngx_int_t
+ngx_read_ahead(ngx_fd_t fd, size_t n)
+{
+    int  err;
+
+    err = posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL);
+
+    if (err == 0) {
+        return 0;
+    }
+
+    ngx_set_errno(err);
+    return NGX_FILE_ERROR;
+}
+
+#endif
+
+
 #if (NGX_HAVE_O_DIRECT)
 
 ngx_int_t

src/os/unix/ngx_files.h

diff --git a/src/os/unix/ngx_files.h b/src/os/unix/ngx_files.h
index 2efd247..ccaf44a 100644
--- a/src/os/unix/ngx_files.h
+++ b/src/os/unix/ngx_files.h
@@ -264,7 +264,7 @@
 
 #define NGX_HAVE_READ_AHEAD      1
 
-#define ngx_read_ahead(fd, n)    posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL)
+ngx_int_t ngx_read_ahead(ngx_fd_t fd, size_t n);
 #define ngx_read_ahead_n         "posix_fadvise(POSIX_FADV_SEQUENTIAL)"
 
 #else