On Tue, 19 Jun 2007 22:59:51 -0700, Arjan van de Ven wrote: > user does on FS A: > mkdir /mnt/A/somedir > touch /mnt/A/somedir/somefile > > and then 2 things happen in parallel > 1) touch /mnt/B/somefile > 2) mv /mnt/union/somedir /mnt/union/somefile > > since the underlying FS for 2) is FS A... how will this work out locking > wise? Will the VS lock the union directory only? Or will this operate > only on the underlying FS? How is dcache consistency guaranteed for > scenarios like this?
Ok, with Christophs help I guess I know now what the question is :) touch /mnt/B/somefile is doing a lookup in "B" for "somefile". Therefore it locks B->i_mutex for that. When it gets a negative dentry it creates the file. mv /mnt/union/somedir /mnt/union/somefile is doing a lookup in "union" for "somefile". Therefore it first locks the i_mutex of the topmost directory in the union of "/mnt/union" (which happens to be "B"). When it gets a negative dentry it than follows the union down to the next layer (with the topmost directory still locked). Lookup is repeated until a filled dentry is found or the topmost dentry negative dentry is used as a target for the move. Thats it. Did that answer your question? Cheers, Jan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
