On Sat, 10 Feb 2001, Justin T. Gibbs wrote:
> >Are there any reason device drivers do not check if thier devices are
> >writable or not when they are opened ? I think returning an error
> >value, like `od', is the easiest way to avoid this problem.
>
> It is not necessarily sufficient since the media may be changed after
> open on certain types of devices that don't have a media lock. Some
> devices will only tell you that they are write protected on the first
> write, etc. For the devices where we can tell, we should make the check
> in open, but not rely on that catching all cases where a driver will
> return EACCESS.
Also, writing to a write protected sector is a special case of an i/o
error, so it will be handled by non-broken general i/o error handling.
Also^2, write protection might be for individual sectors and might
change while the device is open, just like most i/o errors. We actually
have this for most disks -- FreeBSD has write protection of label
sectors in software, and it can be turned on and off while the device
is open.
Bruce
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