[Nut-upsdev] [Nut-upsuser] Upssched 100% CPU after updating Debian 12

[Sam Varshavchik]

Jim Klimov via Nut-upsuser writes:

> So... determining that FD is to be reaped proved hard. Internet lore suggests  
> fcntl() and poll() on the FD, but it just seems valid to them. The errno is  
> also usually not raised (once I saw a "111: Connection refused" though).
> So the best dumb idea so far is to bail out if we spent the whole loop (128  
> attempts) and only got zero-sized read replies and no errors.

It's been my experience, that the path of least resistance is:

1) The sockets are sets to be non-blocking
2) poll()
3) If poll() says the socket is readable, and read() returns <= 0, then the  
socket is dead. You get no error, and read() returns 0, if the socket had an  
orderly shutdown.

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