On 22 January 2015 at 20:30, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote: > The patch clarifies when blocking may occur while calling > getrandom(). Applied in the draft_getrandom branch. Thanks, Heinrich. Cheers, Michael > Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> > --- > man2/getrandom.2 | 35 ++++++++++++++++++++--------------- > 1 file changed, 20 insertions(+), 15 deletions(-) > > diff --git a/man2/getrandom.2 b/man2/getrandom.2 > index d01502e..cfbbf5f 100644 > --- a/man2/getrandom.2 > +++ b/man2/getrandom.2 > @@ -55,20 +55,17 @@ Therefore > should not be used for Monte Carlo simulations or other > programs/algorithms which are doing probabilistic sampling. > > -.\" FIXME is the following paragraph correct? > By default, > .BR getrandom () > draws entropy from the > .IR /dev/urandom > -pool, and, if that pool has been initialized and > -.IR buflen > -is less than or equal to 256 (see NOTES, below), > -then the call never blocks when drawing from that pool > -and always returns the number of bytes requested in > -.IR buflen . > +pool. > This behavior can be changed via the > .I flags > argument. > +If the > +.IR /dev/urandom > +pool has been initialized, reading from that pool never blocks. > > The > .I flags > @@ -157,17 +154,27 @@ was introduced in version 3.17 of the Linux kernel. > This system call is Linux-specific. > .SH NOTES > .SS Interruption by a signal handler > -.\" FIXME Here, I think there needs to be an opening paragraph that describes > -.\" the cases where getrandom() can block. This should cover the cases with > -.\" GRND_RANDOM and without GRND_RANDOM. Reading the existing page, I am > -.\" still not completely confident that I know what the cases are. > +A call to > +.BR getrandom () > +can only block when called without the > +.B GRND_NONBLOCK > +flag. > +When reading from > +.I /dev/urandom > +.RB ( GRND_RANDOM > +is not set) > +blocking only occurs if the entropy pool has not been initialized yet. > +When reading from > +.I /dev/random > +.RB ( GRND_RANDOM > +is set) > +blocking occurs if not enough random bytes are available. > + > The reaction of > .BR getrandom () > in case of an interruption of a blocking call by a signal > when reading from > .I /dev/urandom > -.RB ( GRND_RANDOM > -is not set) > depends on the initialization state of the entropy buffer > and on the request size > .IR buflen . > @@ -184,8 +191,6 @@ Instead, it will return all of the bytes that have been requested. > .PP > When reading from > .I /dev/random > -.RB ( GRND_RANDOM > -is set) > these guarantees do > .I not > apply. > -- > 2.1.4 > -- 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
