From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60099) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bUneY-00081D-Px for qemu-devel@nongnu.org; Wed, 03 Aug 2016 00:19:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bUneW-0003sj-L9 for qemu-devel@nongnu.org; Wed, 03 Aug 2016 00:19:33 -0400 Date: Wed, 3 Aug 2016 00:19:24 -0400 From: Jeff Cody Message-ID: <20160803041924.GA5270@localhost.localdomain> References: <1470129518-21087-1-git-send-email-famz@redhat.com> <1470129518-21087-2-git-send-email-famz@redhat.com> <1180678412.13134125.1470167146088.JavaMail.zimbra@redhat.com> <20160803023640.GC8117@ad.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160803023640.GC8117@ad.usersys.redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/7] util: Add UUID API List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: Paolo Bonzini , kwolf@redhat.com, mdroth@linux.vnet.ibm.com, qemu-block@nongnu.org, sw@weilnetz.de, qemu-devel@nongnu.org, armbru@redhat.com, mreitz@redhat.com On Wed, Aug 03, 2016 at 10:36:40AM +0800, Fam Zheng wrote: > On Tue, 08/02 15:45, Paolo Bonzini wrote: > > > > > > ----- Original Message ----- > > > From: "Fam Zheng" > > > To: qemu-devel@nongnu.org > > > Cc: famz@redhat.com, berrange@redhat.com, pbonzini@redhat.com, kwolf@redhat.com, mreitz@redhat.com, > > > mdroth@linux.vnet.ibm.com, armbru@redhat.com, sw@weilnetz.de, qemu-block@nongnu.org > > > Sent: Tuesday, August 2, 2016 11:18:32 AM > > > Subject: [PATCH 1/7] util: Add UUID API > > > > > > A number of different places across the code base use CONFIG_UUID. Some > > > of them are soft dependency, some are not built if libuuid is not > > > available, some come with dummy fallback, some throws runtime error. > > > > > > It is hard to maintain, and hard to reason for users. > > > > > > Since UUID is a simple standard with only a small number of operations, > > > it is cleaner to have a central support in libqemuutil. This patch adds > > > qemu_uuid_* the functions so that all uuid users in the code base can > > > rely on. Except for qemu_uuid_generate which is new code, all other > > > functions are just copy from existing fallbacks from other files. > > > > How is g_random_* seeded? > > According to glib doc: > > > GLib changed the seeding algorithm for the pseudo-random number generator > > Mersenne Twister, as used by GRand. > > The urandom source is /dev/urandom (or time based if unavailable). > > (RFC 4122 explicitly accepts pseudo-random.) > > Fam > To piggyback on Fam's answer: It is as if qemu called g_rand_new() [1] for a global static GRand struct. The g_random_* functions use the glib default global GRand struct. If you don't set the global seed yourself with g_random_set_seed(), then the first call into one of the g_random_ functions will create the global GRand struct seeded from /dev/urandom (if available), or the current time (if /dev/urandom is not available). [1] https://developer.gnome.org/glib/stable/glib-Random-Numbers.html#g-rand-new -Jeff