From: "Henrik Rydberg" <rydberg@euromail.se>
To: Kevin Daughtridge <kevin@kdau.com>
Cc: Jiri Slaby <jslaby@suse.cz>, Jiri Kosina <jkosina@suse.cz>,
linux-input@vger.kernel.org, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] HID: leave dev_rdesc unmodified and use it for comparisons
Date: Wed, 19 Sep 2012 20:32:31 +0200 [thread overview]
Message-ID: <20120919183231.GA603@polaris.bitmath.org> (raw)
In-Reply-To: <5059F872.3080203@kdau.com>
Hi Kevin,
Thanks for looking to this.
> Hmm. I hadn't noticed that the other drivers are returning a static
> structure. In that case, it seems that report_fixup itself is broken
> from a memory perspective, in that it returns pointers to
> inconsistent storage types depending on the driver.
The driver can either modify the existing buffer, of return a pointer
to a buffer managed by the driver. The former requires a kmemdup
before, the latter a kmemdup after.
> 1. Ugly workaround: make a temporary copy of the dev_rdesc, give it
> to report_fixup, make a copy of the return, store that copy in
> rdesc, free the temporary copy. Though ugly, this would at least
> involve the smallest diff.
Yes, it is correct and ugly, in no particular order.
> 2. Standardize the behavior of the drivers' report_fixup
> implementations. Given that some of them need to change the size of
> the descriptor, modifying the passed structure is not an option.
> Probably all of them should return a newly allocated structure,
> either a modified copy of the input or a copy of their static, that
> can then be stored directly in rdesc. Especially since report_fixup
> is only ever called right before a copy is going to be taken anyway.
Relying on the returned pointer to be properly alloc'd is not a good
idea, in particular since it changes semantics rather drastically.
Since the current function performs two different things, perhaps
there should be two different functions instead.
> (Adding constness to a parameter isn't considered a severe ABI
> break, is it?)
Inside the kernel there is no ABI. Go wild.
Thanks,
Henrik
next prev parent reply other threads:[~2012-09-19 18:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-19 2:36 [PATCH v2] HID: leave dev_rdesc unmodified and use it for comparisons Kevin Daughtridge
2012-09-19 8:05 ` Jiri Slaby
2012-09-19 16:53 ` Kevin Daughtridge
2012-09-19 18:32 ` Henrik Rydberg [this message]
2012-09-19 11:47 ` Sergei Shtylyov
2012-09-19 11:55 ` Jiri Kosina
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