[CC += LKML] Eric, Jan, (or anyone) Can you offer any insight on Heinrich's question, below? Cheers, Michael On Sun, Apr 13, 2014 at 4:05 PM, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: > On 06.04.2014 14:18, Michael Kerrisk (man-pages) wrote: >>> >>> == >>> > >>> > >> I notice that the FDs returned by read()s from the FAN FD have the >>> > >> FMODE_NONOTIFY flag (fcntl(F_GETFL)) flag set. If you know what >>> > that's >>> > >> about, it would be good to say something about. But, if not, do not >>> > >> worry--just place a FIXME in the page source of fanotify(7) >>> > >>> >Fixed in fanotify.7 >>> >If the listener accesses the file through the file descriptor provided >>> >no additional events are created. >> >> Ahh -- thanks for filling in that piece. I see that you refer to >> fcntl(2) when discussing that flag. But fcntl(2) does not >> mention that flag. I would rather see an explanation of this flag >> in the fanotify pages. >> > > I wrote a small test program and found: > > The flag FMODE_NONOTIFY can be read by function fcntl from userspace. > int flag = fcntl(fd, F_GETFL) > > In include/uapi/asm-generic/fcntl.h I found the following comment: > > /* > * FMODE_EXEC is 0x20 > * FMODE_NONOTIFY is 0x1000000 > * These cannot be used by userspace O_* until internal and external open > * flags are split. > * -Eric Paris > */ > > The definition of FMODE_NONOTIFY is in include/linux/fs.h but this > include is only used to compile the Kernel and not supposed to be used by > userspace. > > I think it is quite annoying that fcntl can return a flag that is not > described in the manpage of fcntl and that is not defined in fcntl.h. > > But FMODE_NONOTIFY is not the only flag: > > I was able to pass > 0x20 (FMODE_EXEC), and > 0x800 (FMODE_NOCMTIME) > to fanotify_init and received them as flag in the file descriptors for the > fanotify events. > I wonder why fanotify_init does not check import parameter event_f_flags and > return an error if any inappropriate value is set. > > Should I put this into the BUGS section? > > Should the name of the flag FMODE_NONOTIFY be mentioned at all in the man > pages? > > Or should we write: > > .I fd > This is an open file descriptor for the object being accessed or > .B FAN_NOFD > if a queue overflow occurred. > The file descriptor can be used to access the contents of the monitored file > or > directory. > It has an internal flag set, that suppresses fanotify event generation. > Hence when the receiver of the fanotify event accesses the notified file or > directory using this file descriptor no additional events will be created. > The reading application is responsible for closing the file descriptor. > > Best regards > > Heinrich Schuchardt -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
