Messages in this thread | | | Date | Tue, 9 Dec 2014 16:15:04 +0000 (UTC) | From | Keith Busch <> | Subject | Re: [PATCH] misc: Increase available dyanmic minors |
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On Tue, 9 Dec 2014, Arnd Bergmann wrote: > On Monday 08 December 2014 16:01:50 Keith Busch wrote: >> This increases the number of available miscellaneous character device >> dynamic minors from 63 to the max minor, 1M. >> >> Dynamic minor previously started at 63 and went down to zero. That's not >> enough in some situations, and also eventually creates a collision with >> 'psaux' misc device. This patch starts minors at the last defined misc >> minor (255) and works up to the max possible. >> >> Signed-off-by: Keith Busch <keith.busch@intel.com> > > I guess this will break support for ancient user space tools, and > possibly also old file systems that do not support more than 8-bit > minor numbers. I would assume that it's ok, but you definitely have > to mention in the changelog that things might break and how you > have concluded that this is safe enough.
Sure, I can call this out in the change log. I hadn't considered file systems on a character device. Tooling as well.
If a character device is so tightly coupled to such legacy tools, maybe they should register a static minor, and this patch makes 63 additional ones available. Does that sound reasonable?
> If you cannot come up with a good reasoning, it might be better > to combine both and use up the traditional dynamic minor numbers > before using the >255 range.
A problem with the existing method is that anyone can use a number in the range it's dynamically allocating from. Once you encounter a collision, all following dynamic misc_device registration will fail. Most of the defined minors in that range are marked unused, but PSMOUSE_MINOR is still used.
If we continue using the traditional dynamic allocator, the component registering as dynamic races against the one registering with its static, so that doesn't sound right.
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