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From: lee@sed170.HAC.COM (John Lee)
Newsgroups: comp.sys.amiga.tech
Subject: Determining disk devices
Summary: Can it be done better?
Message-ID: <331@sed170.HAC.COM>
Date: 4 Jan 90 22:55:15 GMT
Reply-To: lee@sed170.UUCP (John Lee)
Organization: Hughes Aircraft Co., El Segundo, CA
Lines: 32

Currently, the "Official" way of determining the list of disk devices is to
walk down the AmigaDOS device list, looking for entries for devices that
have a non-NULL name and are resident (Task field non-zero), like this:

	/* Pseudo-code */
	for (devent = Device List; devent != NULL; devent = devent->next) {
	    if ((devent's Type is device) && (devent's Task is non-zero)
		    && (devent's Name is non-zero)) {
		(devent is entry for a disk device)
	    }
	}


While this does indeed locate all disk (i.e. directory-oriented) devices,
it can also mistakenly return other devices, such as PIPE:.  To illustrate
this, startup DPaint 1.3 and bring up the Load file-requester.  Note that
PIPE: does not show up in the device buttons.  Now exit DPaint, copy
something to 1.3's PIPE: (perhaps "run dir >PIPE:a"), let that hang and
then startup DPaint 1.3 again.  Notice that PIPE: now shows up in the Load
file-requester.

My question is simple.  How do you make sure you locate only disk devices,
and not merely all devices that are resident and have a name?

--John
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