On 06/08/15 14:35, Laurent Vivier wrote: > > > On 06/08/2015 14:05, Thomas Huth wrote: >> On 06/08/15 13:26, Laurent Vivier wrote: >>> Hi, >>> >>> As "/dev/random" can be blocking perhaps it is possible/better to use >>> the QEMU rng backend instead ? >> >> Actually, I tried to use the rng backends first ... but they turned out >> to be horrible for being used in a synchronous call like I need here: >> You've got to install a callback function which is called at a "random" >> point in time when some data becomes available - and it is even called >> with less bytes than you requested! (i.e. I requested 8 bytes, but the >> callback got only called with 6 bytes). So to use it, I'd have to >> introduce a ring buffer or something similar to query enough random data >> in advance - and when it runs empty, the H_RANDOM hypercall would need >> to block again anyway. >> >> So instead of introducing a hard-to-understand-and-maintain "monster >> wrapper" around the rng backend functions, I think the short and easy >> understandable qemu_random() implementation in this patch here is the >> better choice. >> >> And looking at https://patchwork.ozlabs.org/patch/497062/ I think it >> also should not hurt too much that qemu_random() might be slow here >> since the real hardware number generator is apparently also not very fast. > > It seems a good choice... > > Why do you use buffered file descriptor, fopen/fread/fclose instead of > open/read/close ?
You mean to avoid that fread gets some additional bytes in advance? ... that might be a good idea, thanks, I'll change my patch accordingly. Thomas
