From mboxrd@z Thu Jan 1 00:00:00 1970 From: pnr@planet.nl (Paul Ruizendaal) Date: Tue, 14 Feb 2017 13:27:48 +0100 Subject: [TUHS] Another odd comment in V6 In-Reply-To: References: <378063CD-9B94-4AE3-B4BB-F41D2F6BFBF6@planet.nl> Message-ID: <0B8503D7-D696-4BB6-A2C7-75A95B603036@planet.nl> Hi Nick, Many thanks for that background! I think the quote from the Gabriel paper indeed refers to software interrupts, i.e. signals -- it would not make sense otherwise. The ITS system that the MIT guy referred to is 'large', it ran on PDP10 mainframes. I understand how executing a signal handler is piggy-backed on the return from kernel mode. However, when the signal handler is finished it could either continue with the next instruction or re-excute the system call trap instruction. See http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/src/sys/sys/trap.c (towards end) for details how this is actually done in 2.9BSD. I think you referred to that mechanism as well. However, my question remains: why is that mysterious comment there, above ttread() in V6, and is there a link with the Gabriel story? Paul On 14 Feb 2017, at 12:27 , Nick Downing wrote: > Well I don't know about this actual conversation in history so I can't > help with that. But I can describe how interrupted system calls work. > [..more..]