linux-kernel - Re: [PATCH] char/mem: Make /dev/port less obviously broken (v0)

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Message-ID: <20120207001558.GA30840@kroah.com>
Date:	Mon, 6 Feb 2012 16:15:58 -0800
From:	Greg KH <greg@...ah.com>
To:	Adam Jackson <ajax@...hat.com>
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH] char/mem: Make /dev/port less obviously broken (v0)

On Mon, Feb 06, 2012 at 06:02:02PM -0500, Adam Jackson wrote:
> Did you know /dev/port turns all reads and writes into a stream of inb
> and outb?  Turns out hardware really does care about I/O cycle size
> though, and if you're trying to do an outl four outb's is very much not
> the same thing.
> 
> However, someone somewhere probably built some code and hardware that
> relies on that behaviour.  Plus, userspace needs to be able to tell
> whether the kernel will do the right thing, and fall back to raw port
> access if not.  So add an ioctl to request new 'strict' semantics, which
> allows only exactly 1/2/4 byte cycles and translates them into the
> corresponding I/O cycle size.  This matches the behaviour of sysfs's
> resourceN files for I/O BARs.

Who would use this new ioctl?  And if it's been working ok until now,
why is it needed?

If you want something "new" like this, why not just create /dev/ioport
or something like that to always use the proper alignment and not need
an ioctl at all?

thanks,

greg k-h
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