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    SubjectRe: Regression - /proc/kmsg does not (always) block for 1-byte reads
    Kay, this needs to be fixed.

    Suggested fix: just use the 'seq_printf()' interfaces, which do the
    proper buffering, and allow any size reads of various packetized data.

    Of course, I'd also suggest that whoever was the genius who thought it
    was a good idea to read things ONE F*CKING BYTE AT A TIME with system
    calls for each byte should be retroactively aborted. Who the f*ck does
    idiotic things like that? How did they noty die as babies, considering
    that they were likely too stupid to find a tit to suck on?

    Linus

    On Fri, Jul 6, 2012 at 12:38 PM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
    > On Fri, 6 Jul 2012 20:45:44 +0300
    > Jukka Ollila <jiiksteri@gmail.com> wrote:
    >
    >> Hello,
    >>
    >> A few days ago I filed a kernel regression report concerning a change
    >> in /proc/kmsg behaviour with short reads:
    >>
    >> https://bugzilla.kernel.org/show_bug.cgi?id=44211
    >>
    >> The comments suggest that this is probably intentional, but that it
    >> would be best make sure that the current semantics wrt short reads are
    >> as intended.
    >>
    >> The problem appears on a Debian (unstable) system that drains
    >> /proc/kmsg into a separate fifo read by klogd(8):
    >>
    >> /bin/dd bs=1 if=/proc/kmsg of=/var/run/klogd/kmsg
    >>
    >> With the recent kernel logging changes this /bin/dd exits immediately,
    >> as 1-byte reads are shorter than any log message could possibly be and
    >> read() returns 0. No dd feeding the fifo results in no logging and a
    >> rather unhappy klogd on the reading end of /var/run/klogd/kmsg.
    >>
    >> I suppose a safe solution is to only do reads that are big enough for
    >> any single kernel message, but this is still a change that affects
    >> user space being shipped, so some might find it surprising.
    >>
    >> I don't know what other distros do. Is it just Debian being the odd one out?
    >
    > If this is observed on an actual standard distro userspace and breaks it
    > then its a regression and it needs fixing or reverting.
    >
    > Cc'ing Linus


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