Hi This series of patches implements discard, write_zeroes and secure_erase support for the brd driver. Zdenek asked me to write it, because we use brd in the lvm2 testsuite and it would be benefical to run the testsuite with discard enabled in order to test discard handling. This patch series should have no performance impact - it doesn't add any locks to the common I/O paths. It only extends rcu read region around lookup and reading or writing of a single page. Discarded pages are freed with "call_rcu" to make sure that if we mix discard with I/O, the I/O won't access freed memory. Mikulas
