Hi Evgeniy, On 09/04/18 02:49, Evgeniy Polyakov wrote: > Hi everyone > > Sorry for that late reply > > 01.03.2018, 21:58, "Stefan Strogin" <sstro...@cisco.com>: >> So I was thinking to add these two fields to union event_data: >> task->signal->group_exit_code >> task->signal->flags >> This won't increase size of struct proc_event (because of comm_proc_event) >> and shouldn't break backward compatibility for the user-space. But it will >> add some useful information about what caused the process death. >> What do you think, is it an acceptable approach? > > As I saw in other discussion, doesn't it break userspace API, or you are sure > that no sizes has been increased? > You are using the same structure as used for plain signals and add group > status there, how will userspace react, > if it was compiled with older headers? What if it uses zero-field alignment, > i.e. allocating exactly the size of structure with byte precision? >
Please ignore this RFC, I was wrong about the fields I need for the problem. I have sent this patch: https://lkml.org/lkml/2018/3/29/531, would be grateful for a review. As for breaking UAPI and structure sizes, look: > struct proc_event { ... > union { /* must be last field of proc_event struct */ ... > struct comm_proc_event { > __kernel_pid_t process_pid; > __kernel_pid_t process_tgid; > char comm[16]; > } comm; __kernel_pid_t is int that is always 4 bytes in Linux, then sizeof(event_data.comm) == 24 on all platforms. > > struct coredump_proc_event { > __kernel_pid_t process_pid; > __kernel_pid_t process_tgid; > + __kernel_pid_t parent_pid; > + __kernel_pid_t parent_tgid; > } coredump; sizeof(event_data.coredump) == 16 > > struct exit_proc_event { > __kernel_pid_t process_pid; > __kernel_pid_t process_tgid; > __u32 exit_code, exit_signal; > + __kernel_pid_t parent_pid; > + __kernel_pid_t parent_tgid; > } exit; sizeof(event_data.exit) == 24 > > } event_data; > }; Therefore, sizeof(event_data) is always = 24 - with old headers and new ones. sizeof(struct proc_event) is the same as well. Hence user-space software with old and new headers will allocate the same size. If the user-space program somehow allocates space only for an internal structure, e.g. for event_data.exit, I still don't see any problems if it allocates and handles only first 16 bytes of the structure using old headers. -- Stefan
