tree bec5bed13a74539d2741334593cdd7f2fc4241c5
parent 6fda135c908d0f38a0167adcbd71094572e3059b
author Jan Beulich <JBeulich@suse.com> 1340379369 +0100
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1340739456 -0700

syslog: fill buffer with more than a single message for SYSLOG_ACTION_READ

The recent changes to the printk buffer management resulted in
SYSLOG_ACTION_READ to only return a single message, whereas previously
the buffer would get filled as much as possible. As, when too small to
fit everything, filling it to the last byte would be pretty ugly with
the new code, the patch arranges for as many messages as possible to
get returned in a single invocation. User space tools in at least all
SLES versions depend on the old behavior.

This at once addresses the issue attempted to get fixed with commit
b56a39ac263e5b8cafedd551a49c2105e68b98c2 ("printk: return -EINVAL if
the message len is bigger than the buf size"), and since that commit
widened the possibility for losing a message altogether, the patch
here assumes that this other commit would get reverted first
(otherwise the patch here won't apply).

Furthermore, this patch also addresses the problem dealt with in
commit 4a77a5a06ec66ed05199b301e7c25f42f979afdc ("printk: use mutex
lock to stop syslog_seq from going wild"), so I'd recommend reverting
that one too (albeit there's no direct collision between the two).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kay Sievers <kay@vrfy.org>
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>