Why is getentropy marked with warn_unused_result?

[Adhemerval Zanella]

On 27/07/2017 21:12, Joseph Myers wrote:
> On Sun, 23 Jul 2017, Florian Weimer wrote:
> 
>> I'm still open to implementing emulation within glibc if problems like
>> these convince the glibc community that this is necessary.
> 
> I don't object to a straightforward emulation that opens /dev/urandom with 
> O_CLOEXEC, does the read and closes the file, each time getentropy is 
> called (if __NR_getrandom is not defined, or if the getrandom syscall 
> returns an ENOSYS error).  The argument for emulation in getentropy is 
> stronger than that for emulating the lower-level getrandom interface.
> 

If I recall correctly (and the summary at [1] helped as well), the main
issue with the getentropy emulation is how to handle correctly any file
operation issue (non existent urandom file for some reason, EMFILE/ENFILE,
ENOMEM) which leads to different function semantic whether the emulation
is used. 

[1] https://lwn.net/Articles/711013/