On Wed, 2014-09-24 at 08:49 +0100, Ingo Molnar wrote: > * Pawel Moll <pawel.moll@xxxxxxx> wrote: > > > On Thu, 2014-09-18 at 15:34 +0100, Pawel Moll wrote: > > > This patch adds a PERF_COUNT_SW_USERSPACE_EVENT type, > > > which can be generated by user with PERF_EVENT_IOC_ENTRY > > > ioctl command, which injects an event of said type into > > > the perf buffer. > > > > It occurred to me last night that currently perf doesn't handle "write" > > syscall at all, while this seems like the most natural way of > > "injecting" userspace events into perf buffer. > > > > An ioctl would still be needed to set a type of the following events, > > something like: > > > > ioctl(SET_TYPE, 0x42); > > write(perf_fd, binaryblob, size); > > ioctl(SET_TYPE, 0); > > dprintf(perf_fd, "String"); > > > > which is fine for use cases when the type doesn't change often, > > but would double the amount of syscalls when every single event > > is of a different type. Perhaps there still should be a > > "generating ioctl" taking both type and data/size in one go? > > Absolutely, there should be a single syscall. Yeah, it's my gut feeling as well. I just wonder if we still want to keep write() handler for operations on perf fds? This seems natural - takes data buffer and its size. The only issue is the type. > I'd even argue it should be a new prctl(): that way we could both > generate user events for specific perf fds, but also into any > currently active context (that allows just generation/injection > of user events). In the latter case we might have no fd to work > off from. When Arnaldo suggested that the "user events" could be used by perf trace, it was exactly my first thought. I just didn't have answer how to present it to the user (an extra syscall didn't seem like a good idea), but prctl seems interesting, something like this? prctl(PR_TRACE_UEVENT, type, size, data, 0); How would we select tasks that can write to a given buffer? Maybe an ioctl() on a perf fd? Something like this? ioctl(perf_fd, PERF_EVENT_IOC_ENABLE_UEVENT, pid); ioctl(perf_fd, PERF_EVENT_IOC_DISABLE_UEVENT, pid); It could set/clear a flag in pid's task_struct (but probably not in the "normal" flags, as they are only supposed to be set by owner and in ptrace/fork case) and a pointer to the task in perf_event(_context). Or maybe some variation on ptrace would be more in place? This would also solve issue of permission checking (if the profiling tool can ptrace the process, it can also enable/disable its uevent generation capability). Paweł Or maybe it should go through ptrace? -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
