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Re: [Info-mtools] operation not permitted while setting disk parameters

From: Frank Loeffler
Subject: Re: [Info-mtools] operation not permitted while setting disk parameters in find_device
Date: Thu, 20 May 2021 18:30:59 +0200
User-agent: Mutt/1.10.1 (2018-07-13)

Hi Alain,

On Thu, May 20, 2021 at 01:18:54PM +0200, Alain Knaff wrote:
[ snipped ... minfo RDWR for ioctl ]

Now, off the top of my head, I can't see right now where minfo would
need to issue an ioctl that needs write access. Care to elaborate?

Sure. The long story can be found here:

The short story is: drives have to be configured according to the floppy
parameters (number of sectors/cylinders) to be able to read the entire floppy. The way this is usually handled (also in mtools) is to read the boot sector (that you assume you can always read), from there extract the necessary parameters, configure the drive accordingly and then go on reading the rest of the floppy.

The issue at hand is that even when you only want to read a floppy, you need to configure the device accordingly to do so, and configuring the device needs write permissions on that device (which may be different than the media itself). When opening the device only with RO permission but trying to configure it according to the information in the boot sector (as mtools does without this change), you get an error like

Can't set disk parameters for B: Operation not permitted
Cannot initialize 'B:'

Indeed, just making minfo require write access unconditionally is
certainly not a good idea, as it would make minfo inaccessible to users
which otherwise can't have write access (permissions, or simply
write-protected media).

I believe (but am not sure now) that I also tried write-protected media with this change, and it worked. This would also make sense as you _have_ to open the device in rw-mode in order to configure it and that is necessary to read it in the first place.


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