Hi all. I am trying to mount a flat file system by simple_file_server in l4vfs tree and then navigating over the file systen, i.e. opening/reading the root directory by opendir()/readdir(), searching the files in the directory and then opening them by open(). Doing this, I found that opendir() sometimes fails, trying to allocate a big (almost 2 gigabytes) dataspace at dm_phys. When I tried to compile my program and l4vfs servers with debug output, I had seen that this is done by calloc() function in opendir() function in l4\pkg\uclibc\lib\contrib\uclibc\libc\misc\dirent\opendir.c: if (!(ptr->dd_buf = calloc(1, ptr->dd_max))) { free(ptr); nomem_close_and_ret: close(fd); __set_errno(ENOMEM); return NULL; } before that, it makes fstat() and assigns ptr->dd_max to a FS block size from the stat buffer. After looking into l4vfs backends and simple_file_server, I had seen that the FS block size is left undefined, so it tried to use a big random value which appeared to be in a stat buffer. So, the fix can be simple -- set FS blksize to something (I set it to 512 bytes). And also, I added copying of that size from the stat buffer in stat() and fstat() functions in libc l4vfs io backend. So, my patch is attached to this letter WBR, valery