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" <f...@redhat.com> > > > To: qemu-de...@nongnu.org > > > Cc: f...@redhat.com, berra...@redhat.com, pbonz...@redhat.com, > > > kw...@redhat.com, mre...@redhat.com, > > > mdr...@linux.vnet.ibm.com, arm...@redhat.com, s...@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
