On Thu, 2018-04-19 at 13:26 -0400, Jerome Glisse wrote: > On Thu, Apr 19, 2018 at 12:58:39PM -0400, Jeff Layton wrote: > > On Thu, 2018-04-19 at 12:30 -0400, Jerome Glisse wrote: > > > On Thu, Apr 19, 2018 at 07:43:56AM -0700, Matthew Wilcox wrote: > > > > On Thu, Apr 19, 2018 at 10:38:25AM -0400, Jerome Glisse wrote: > > > > > Oh can i get one more small slot for fs ? I want to ask if they are > > > > > any people against having a callback everytime a struct file is added > > > > > to a task_struct and also having a secondary array so that special > > > > > file like device file can store something opaque per task_struct per > > > > > struct file. > > > > > > > > Do you really want something per _thread_, and not per _mm_? > > > > > > Well per mm would be fine but i do not see how to make that happen with > > > reasonable structure. So issue is that you can have multiple task with > > > same mm but different file descriptors (or am i wrong here ?) thus there > > > would be no easy way given a struct file to lookup the per mm struct. > > > > > > So as a not perfect solution i see a new array in filedes which would > > > allow device driver to store a pointer to their per mm data structure. > > > To be fair usualy you will only have a single fd in a single task for > > > a given device. > > > > > > If you see an easy way to get a per mm per inode pointer store somewhere > > > with easy lookup i am all ears :) > > > > > > > I may be misunderstanding, but to be clear: struct files don't get > > added to a thread, per-se. > > > > When userland calls open() or similar, the struct file gets added to > > the files_struct. Those are generally shared with other threads within > > the same process. The files_struct can also be shared with other > > processes if you clone() with the right flags. > > > > Doing something per-thread on every open may be rather difficult to do. > > Basicly i want a callback in __fd_install(), do_dup2(), dup_fd() and > add void * *private_data; to struct fdtable (also a default array to > struct files_struct). The callback would be part of struct file_operations. > and only call if it exist (os overhead is only for device driver that > care). > > Did i miss something fundamental ? copy_files() call dup_fd() so i > should be all set here. > > I will work on patches i was hoping this would not be too much work. > No, I think I misunderstood. I was thinking you wanted to iterate over all of the threads that might be associated with a struct file, and that's rather non-trivial. A callback when you add a file to the files_struct seems like it would probably be OK (in principle). -- Jeff Layton <jlayton@xxxxxxxxxx>
