Adjusted file->sys_offset after the write() syscall. This fixes suboptimal behavior caused by surplus lseek() for sequential writes on systems without pwrite(). A consecutive read after write might result in an error on systems without pread() and pwrite(). Fortunately, at the moment there are no widely used systems without these syscalls.

--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -226,6 +226,7 @@ ngx_write_file(ngx_file_t *file, u_char 
             return NGX_ERROR;
         }
 
+        file->sys_offset += n;
         file->offset += n;
         written += n;