A bit more info in case anyone is interested...
I enable tracing and found something interesting. It seems that the number of
entropy bits go negative at some point:
<...>-28916 [002] 535863.435655: extract_entropy: input pool: nbytes 8
entropy_count 3646 caller xfer_secondary_pool+0xaa/0x10c
<...>-28916 [002] 535863.435662: mix_pool_bytes_nolock: input pool: bytes 20
caller extract_buf+0xc0/0x154
<...>-28916 [002] 535863.435664: mix_pool_bytes: blocking pool: bytes 8 caller
xfer_secondary_pool+0xc6/0x10c
<...>-28916 [002] 535863.435665: credit_entropy_bits: blocking pool: bits 64
entropy_count 64 entropy_total 1024 caller xfer_secondary_pool+0xd4/0x10c
<...>-28916 [002] 535863.435672: mix_pool_bytes_nolock: blocking pool: bytes 20
caller extract_buf+0xc0/0x154
<...>-28919 [003] 535863.437207: extract_entropy_user: blocking pool: nbytes 4
entropy_count 32 caller random_read+0x60/0x150
<...>-28919 [003] 535863.437212: mix_pool_bytes_nolock: blocking pool: bytes 20
caller extract_buf+0xc0/0x154
<...>-28924 [001] 535863.439902: extract_entropy: nonblocking pool: nbytes 16
entropy_count -32 caller get_random_bytes+0x38/0x48
<...>-28926 [003] 535863.440827: extract_entropy: nonblocking pool: nbytes 16
entropy_count -32 caller get_random_bytes+0x38/0x48
And that's what's causing no data to be returned. Haven't figured out yet why
it goes negative.
But, I was able to semi-correct the issue by running the following:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <linux/random.h>
int
main(int argc, char *argv[])
{
int fd = open("/dev/urandom", O_RDWR);
if (fd)
{
ioctl(fd, RNDCLEARPOOL);
perror("error");
close(fd);
}
}
I now get data back:
pzsfs101:~ # dd if=/dev/urandom of=/dev/null count=10
10+0 records in
10+0 records out
5120 bytes (5.1 kB) copied, 0.00164344 s, 3.1 MB/s
And the dynamic UUID looks better now:
pzsfs101:~ # grep '' /proc/sys/kernel/random/*
/proc/sys/kernel/random/boot_id:00000000-0000-4000-8000-000000000000
/proc/sys/kernel/random/entropy_avail:2179
/proc/sys/kernel/random/poolsize:4096
/proc/sys/kernel/random/read_wakeup_threshold:64
/proc/sys/kernel/random/uuid:af2ccaee-221b-4128-ab5a-389eb7eaa3fd
/proc/sys/kernel/random/write_wakeup_threshold:1024
And it updates as it should each time the it is read.
Anyway, still no idea exactly what happened.
Leland
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