On Thu, Jan 10, 2013 at 10:47 AM, Andrey Wagin <avagin@xxxxxxxxx> wrote: > 2012/12/28 Oleg Nesterov <oleg@xxxxxxxxxx>: >> On 12/28, Andrey Vagin wrote: >>> >>> signalfd should be called with the flag SFD_RAW for that. >>> >>> signalfd_siginfo is not full for siginfo with a negative si_code. >>> copy_siginfo_to_user() is copied a full siginfo to user-space, if >>> si_code is negative. signalfd_copyinfo() doesn't do that and can't be >>> expanded, because it has not compatible format with siginfo_t. >>> >>> Another problem is that a constant __SI_* is removed from si_code. >>> It's not a problem for usual applications, because they expect >>> a defined type of siginfo (internal logic). >>> When we want to dump pending signals, we can't predict a type of >>> siginfo, so we should get it from kernel. >>> >>> The main idea of the raw format is that it should be enough for >>> restoring exactly the same siginfo for the current process. >>> >>> This functionality is required for checkpointing pending signals. >> >> And this should be used along with pread(). >> >> I won't argue, but perhaps we should simply postulate that pread() >> always dumps siginfo in raw format and avoid the new flag? > > I won't argue too:), but I think the flag is more flexiable. The flag > allows to get raw siginfo from read(), it may be useful not only for > checkpoint/restore. pread with offset = 0 is equal to read(), so the > interface with the flag is more clear. Special casing pread() behavior for signalfd() so that SFD_RAW is not required seems only to make the ugliness worse... While I appreciate the need for this API, multiplexing a queue selector and a positional value into what is normally a byte offset in pread() is really bizarre. This is ugly and I wonder if something better is possible, though so far I have no suggestions beyond adding a new system call. -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
