linux-kernel - Re: Ctrl+C doesn't interrupt process waiting for I/O

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Message-ID: <48672ADE.1090300@goop.org>
Date:	Sat, 28 Jun 2008 23:25:34 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Avi Kivity <avi@...ranet.com>
CC:	Török Edwin <edwintorok@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Ctrl+C doesn't interrupt process waiting for I/O

Avi Kivity wrote:
> Applications should not assume that write() (or other syscalls) can't 
> return EINTR.  Not all filesystems have a bounded-time backing store.

The distinction between 'fast' (filesystem) and 'slow' (terminals and 
pipes) blocking syscalls goes back to the earliest days of Unix, and is 
part of the ABI.  Most filesystem syscalls are not documented to ever 
return EINTR.

> 'soft' has its own problems; namely false positives when someone steps 
> on the network cable, temporarily blocking packet flow, or when using 
> a clustered server which may take some time to recover from a fault.

Sure.  It's the basic problem of trying to make network access 
transparent by hiding the failure modes.  You either need to put up with 
spurious timeouts caused by transient failures, or unbounded blocking on 
real failures.

Regardless, NFS is the exception here, and making normal block-backed 
filesystems start throwing EINTRs around would be a huge behavioural change.

    J
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