Re: short read from /dev/urandom

[hpa@zytor.com (H. Peter Anvin)]

Followup to:  <20050114232154.GB18479@thunk.org>
By author:    "Theodore Ts'o" <tytso@mit.edu>
In newsgroup: linux.dev.kernel
> 
> Good point.  The fact that there are other implementations out there
> which are doing this is a convincing argument.  
> 
> I am still a bit concerned still that a stupidly written program that
> opens /dev/urandom (perhaps unwittingly) and tries to read a few
> hundred megabytes will become uninterruptible until the read
> completes, but I'm not sure it's worth it to but in some kludge that
> says "break if there's a signal and count > 1 megabyte --- otherwise
> we'll return soon enough".
> 

I'm very concerned about this; this is fundamentally a change to
signal delivery semantics.

What we might want to go along with is a read smaller than PIPE_BUF
(the largest size guaranteed to be atomic when writing to a pipe,
which is another special case) should not return fractional.

	-hpa