On Wed, Jun 12, 2019 at 3:52 PM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > On Sat, 2019-06-08 at 16:57 +0300, Amir Goldstein wrote: > > Count struct files open RO together with inode reference count instead > > of using a dedicated i_readcount field. This will allow us to use the > > RO count also when CONFIG_IMA is not defined and will reduce the size of > > struct inode for 32bit archs when CONFIG_IMA is defined. > > > > We need this RO count for posix leases code, which currently naively > > checks i_count and d_count in an inaccurate manner. > > > > Should regular i_count overflow into RO count bias by struct files > > opened for write, it's not a big deal, as we mostly need the RO count > > to be reliable when the first writer comes along. > > "i_count" has been defined forever. Has its meaning changed? This > patch implies that "i_readcount" was never really needed. > Not really. i_count is only used to know if object is referenced. It does not matter if user takes 1 or more references on i_count as long as user puts back all the references it took. If user took i_readcount, i_count cannot be zero, so short of overflow, we can describe i_readcount as a biased i_count. But if I am following Miklos' suggestion to make i_count 64bit, inode struct size is going to grow for 32bit arch when CONFIG_IMA is not defined, so to reduce impact, I will keep i_readcount as a separate member and let it be defined also when BITS_PER_LONG == 64 and implement inode_is_open_rdonly() using d_count and i_count when i_readcount is not defined. Let's see what people will have to say about that... Thanks, Amir.
