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When reading from /dev/random, block at most once in cprng_strong.
We are not obligated to return exactly as many bytes as requested,
and many applications -- notably those that use stdio or otherwise
buffered I/O to read from /dev/random -- try to read many more than
32 bytes at a time from /dev/random even if all they are about to use
is 32 bytes.
In this case, blocking until we have enough entropy to fill a large
buffer causes needless application delays, e.g. causing cgdconfig
(which reads from /dev/random with stdio) to hang at boot when trying
to configure a random-keyed device for swap.
Patch tested by Aran Clauson. Fixes PR kern/48028.
We are not obligated to return exactly as many bytes as requested,
and many applications -- notably those that use stdio or otherwise
buffered I/O to read from /dev/random -- try to read many more than
32 bytes at a time from /dev/random even if all they are about to use
is 32 bytes.
In this case, blocking until we have enough entropy to fill a large
buffer causes needless application delays, e.g. causing cgdconfig
(which reads from /dev/random with stdio) to hang at boot when trying
to configure a random-keyed device for swap.
Patch tested by Aran Clauson. Fixes PR kern/48028.