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    SubjectRe: [PATCH] mmc: block: Add new ioctl to send multi commands
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    On Thu, Sep 10, 2015 at 1:24 AM, Jon Hunter <jonathanh@nvidia.com> wrote:
    ...
    >> - you have some implicit padding after the structure and should replace that
    >> with explictit pad bytes to extend the structure to a multiple of its
    >> alignment (8 bytes).
    >
    > Would padding with __u32 at the end be sufficient here? I assume the
    > __u32 would be 32-bit aligned. However, was not sure if this would
    > always be the case.

    Is there something wrong with implicit padding?
    Only one copy of the structure is passed to the kernel for any given call.

    >>>> struct mmc_ioc_multi_cmd {
    >>>> __u64 num_of_cmds;
    >>>> struct mmc_ioc_cmd cmds[0];
    >>>> };

    I think this would work just as well. But doesn't "pointer to an
    array" require 32-bit ioctl compat handling?
    We were trying to avoid a 32-bit user space compatibility handler.

    >>>> as I said, both are ugly. My first choice would have been the other one,
    >>>> but I'm sure you have some reasons yourself.

    Why do you prefer the alternative you proposed?

    My guess is better type checking (and I would like that too). But
    maybe there is something else?

    cheers,
    grant


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