Re: [Xen-devel] [PATCH for-4.11] libs/gnttab: fix FreeBSD gntdev interface

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Apr 17, 2018 at 02:03:41PM +0100, Roger Pau Monne wrote:
> Current interface to the gntdev in FreeBSD is wrong, and mostly worked
> out of luck before the PTI FreeBSD fixes, when kernel and user-space
> where sharing the same page tables.

where -> were?

> 
> On FreeBSD ioctls have the size of the passed struct encoded in the ioctl
> number, because the generic ioctl handler in the OS takes care of
> copying the data from user-space to kernel space, and then calls the
> device specific ioctl handler. Thus using ioctl structs with variable
> sizes is not possible.
> 
> The fix is to turn the array of structs at the end of
> ioctl_gntdev_alloc_gref and ioctl_gntdev_map_grant_ref into pointers,
> that can be properly accessed from the kernel gntdev driver using the
> copyin/copyout functions. Note that this is exactly how it's done for
> the privcmd driver.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Not sure I follow. Isn't turning the array into pointer still results in
a variable length array?

The code looks sane to me.

Wei.

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