On Thu, Feb 7, 2013 at 10:13 PM, Andrey Wagin <avagin@xxxxxxxxx> wrote: > 2013/2/7 Oleg Nesterov <oleg@xxxxxxxxxx>: >> Andrey, sorry for delay. >> >> As for API, I leave this to you and Michael. Not that I like these >> new flags, but I agree that pread() hack was not pretty too. >> >> On 01/29, Andrey Vagin wrote: [...] >>Damn. But after I wrote this email I realized that llseek() probably can't >> work. Because peek_offset/f_pos/whatever has to be shared with all processes >> which have this file opened. >> >> Suppose that the task forks after sys_signalfd(). Now if parent or child >> do llseek this affects them both. This is insane because signalfd is >> "strange" to say at least, fork/dup/etc inherits signalfd_ctx but not the >> "source" of the data. (Good catch, Oleg.) > So I want to suggest a way how to forbid read() for SIGNALFD_PEEK. > file->f_pos can be initialized to -1. read() returns EINVAL in this > case. In a man page we will write that signals can be dumped only with > help pread(). Is it overload or too ugly? >From an interface perspective I have no problem with limiting the API to allow just pread(). If we later decide that there is some way that the semantics using read() + lseek() could be sensible (which seems unlikely), we could relax things and allow read(). [...] > Oleg, thank you for the comments. I'm waiting an answer on the > question and after that I'm going to send a final version. It would be nice if the new patch series has a changelog of the changes to date, and also includes a fairly detailed description of the user-space API. Would that be possible? Thanks, Michael -- 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
