The patch clarifies when blocking may occur while calling getrandom(). 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 -- 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
