On Mon, 24 Apr 2017 18:39:28 +0300 Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > With current epoll architecture target files are addressed > with file_struct and file descriptor number, where the last > is not unique. Moreover files can be transferred from another > process via unix socket, added into queue and closed then > so we won't find this descriptor in the task fdinfo list. > > Thus to checkpoint and restore such processes CRIU needs to > find out where exactly the target file is present to add it into > epoll queue. For this sake one can use kcmp call where > some particular target file from the queue is compared with > arbitrary file passed as an argument. > > Because epoll target files can have same file descriptor > number but different file_struct a caller should explicitly > specify the offset within. > > To test if some particular file is matching entry inside > epoll one have to > > - fill kcmp_epoll_slot structure with epoll file descriptor, > target file number and target file offset (in case if only > one target is present then it should be 0) > > - call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot) > - the kernel fetch file pointer matching file descriptor @fd of pid1 > - lookups for file struct in epoll queue of pid2 and returns traditional > 0,1,2 result for sorting purpose That's quite a bit more code. Is there a neat way of making it depend on a new CONFIG_foo, then select CONFIG_foo if CONFIG_CHECKPOINT_RESTORE?
