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Re: [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct dmar_drhd_unit

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On Sun, 20 Mar 2016, Wei Yang wrote:

> hdr in struct dmar_drhd_unit is used to point the DMAR hardware unit copied
> at the end of struct dmar_drhd_unit. One zero-sized array may be more
> elegant for this purpose.

You forget to tell why. 
 
> This patch replace *hdr with hdr[0] in struct dmar_drhd_unit.
> 
> Besides this, this patch includes other two changes:
> 1. remove unnecessary type cast in dmar_table_detect()

Again. Why is it not necessary?

> 2. type cast from acpi_dmar_header to acpi_dmar_hardware_unit directly

Don't even think about doing that. container_of() is there for a reason.

Your change works today, because the embedded structure is the first one in
the containing structure. If the containing structure gets reordered later,
the whole thing will explode in hard to debug ways.

Even if such a reordering is unlikely in that ACPI case, we just don't do
that. It's bad and sloppy coding style. The generated code is the same.

Thanks,

	tglx

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[Patch V2 0/4] Code refine for Intel IOMMU Wei Yang <richard.weiyang@gmail.com> - 2016-03-20 15:00 +0100
  [Patch V2 2/4] iommu/vt-d: use zero-sized array in DMAR related ACPI structures Wei Yang <richard.weiyang@gmail.com> - 2016-03-20 15:00 +0100
  [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct dmar_drhd_unit Wei Yang <richard.weiyang@gmail.com> - 2016-03-20 15:00 +0100
    Re: [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct  dmar_drhd_unit Thomas Gleixner <tglx@linutronix.de> - 2016-03-20 16:50 +0100
      Re: [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct  dmar_drhd_unit Wei Yang <richard.weiyang@gmail.com> - 2016-03-21 15:50 +0100
        Re: [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct  dmar_drhd_unit Thomas Gleixner <tglx@linutronix.de> - 2016-03-21 18:00 +0100
          Re: [Patch V2 1/4] iommu/vt-d: replace *hdr with hdr[0] in struct  dmar_drhd_unit Wei Yang <richard.weiyang@gmail.com> - 2016-03-21 23:40 +0100
  [Patch V2 4/4] iommu/vt-d: refine dmar_acpi_dev_scope_init() with dmar_walk_dmar_table() Wei Yang <richard.weiyang@gmail.com> - 2016-03-20 15:00 +0100

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