Path: utzoo!censor!geac!torsqnt!tmsoft!masnet!canremote!bradley.grigor
From: bradley.grigor@canremote.uucp (BRADLEY GRIGOR)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ms-dos FILES=fd in config
Message-ID: <90031103231049@masnet.uucp>
Date: 10 Mar 90 19:01:00 GMT
Organization: Canada Remote Systems Limited, Mississauga, ON, Canada
Lines: 40

dixon@sagittarius.crd.ge.com (walt dixon) comments on my reply:

d.>In a reply to my previous article bradley grigor writes:

d.>[most of message deleted]

>Note: despite the documentation, a child process created with the
>Exec function can only inherit twenty file handles from its
>parent.

d.>One would have thought that this would have been cleaned up in DOS
d.>3.3.  The DOS 3.1 duplicate PSP code which is called by the int 21h
d.>load function (actually at an alternate entry point that sets a flag
d.>indicating an internal request),  the code exlicitly loads a count
d.>of 20 into cx and loops through the JFT.  In this older version of
d.>DOS there was no explicit support for an alternate JFT (although it
d.>worked,  sort of).

d.>The inheritance logic is really pretty simple.  Omiting some details
d.>pertaining to file sharing and network devices,  DOS (in the internal
d.>duplicate PSP function) scans the JFT.  For every open file the mode
d.>field in the SFT is checked looking at the inheritance bit.  If the
d.>bit is set,  the system file number from the JFT is copied to the new
d.>JFT (in the new PSP).  The refernce count in the SFT is incremented
d.>and the device driver is called if it supports open/close requests
d.>and the device is a character or the device is a block device and
d.>file sharing is enabled.  One could duplicate this function if
d.>necessary.

What I said about inheriting only 20 files was also quoted from
the PC Tech Journal article re: function 67H in DOS V3.3.  As to
why -- I might assume that it was considered "too tough" to
allocate extended handle space along with another PSP, so the
developers simply settled for the stock 20-byte handle area in
the new PSP.

bradley.grigor@canremote.uucp  :  ALEX is coming to Toronto in April.
Newmarket, Ontario, Canada     :  TelePoker will be there - will YOU?
---
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