The hwrng core implementation currently doesn't consider the
quality field of the struct hwrng. So the first registered rng
is the winner and further rng sources even with much better
quality are ignored.

The behavior should be that always the best rng with the highest
quality rate should be used as current rng source. Only if the
user explicitly chooses a rng source (via writing a rng name
to /sys/class/misc/hw_random/rng_current) the decision for the
best quality should be suppressed.

This two patches make hwrng always hold a list of registered
rng sources sorted decreasing by quality. On registration of a new
hwrng source the list is updated and if the current rng source was
not chosen by user and the new rng provides better quality set as
new current rng source. Similar on unregistration of an rng, if it
was the current used rng source the one with the next highest quality
is used. If a rng source has been set via sysfs from userland as
long as this one doesn't unregister it is kept as current rng
regardless of registration of 'better' rng sources.

Patch 1 introduces the sorted list of registered rngs and the
always use the best quality behavior.

Patch 2 makes hwrng remember that the user has selected an
rng via echo to /sys/class/misc/hw_random/rng_current and
adds a new sysfs attribute file 'rng_selected' to the rng core.

Harald Freudenberger (2):
  crypto: hwrng use rng source with best quality
  crypto: hwrng remember rng chosen by user

 drivers/char/hw_random/core.c | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)


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