Re: [PATCH v2] HID: leave dev_rdesc unmodified and use it for comparisons

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Media]     [Linux Input]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Old Linux USB Devel Archive]

  Powered by Linux