l4vfs and opendir()/readdir()

Valery V. Sedletski _valerius at mail.ru
Sun Jun 20 12:36:09 CEST 2010

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))) {
		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


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