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

[Wei Yang]

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.

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()
2. type cast from acpi_dmar_header to acpi_dmar_hardware_unit directly

Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
---
 drivers/iommu/dmar.c |   15 ++++-----------
 include/linux/dmar.h |    2 +-
 2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 80e3c17..d6dd23f 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -292,8 +292,7 @@ static int dmar_pci_bus_add_dev(struct dmar_pci_notify_info *info)
 		if (dmaru->include_all)
 			continue;
 
-		drhd = container_of(dmaru->hdr,
-				    struct acpi_dmar_hardware_unit, header);
+		drhd = (struct acpi_dmar_hardware_unit *)dmaru->hdr;
 		ret = dmar_insert_dev_scope(info, (void *)(drhd + 1),
 				((void *)drhd) + drhd->header.length,
 				dmaru->segment,
@@ -390,7 +389,6 @@ static int dmar_parse_one_drhd(struct acpi_dmar_header *header, void *arg)
 	 * If header is allocated from slab by ACPI _DSM method, we need to
 	 * copy the content because the memory buffer will be freed on return.
 	 */
-	dmaru->hdr = (void *)(dmaru + 1);
 	memcpy(dmaru->hdr, header, header->length);
 	dmaru->reg_base_addr = drhd->address;
 	dmaru->segment = drhd->segment;
@@ -529,8 +527,7 @@ static int __init dmar_table_detect(void)
 
 	/* if we could find DMAR table, then there are DMAR devices */
 	status = acpi_get_table_with_size(ACPI_SIG_DMAR, 0,
-				(struct acpi_table_header **)&dmar_tbl,
-				&dmar_tbl_size);
+				&dmar_tbl, &dmar_tbl_size);
 
 	if (ACPI_SUCCESS(status) && !dmar_tbl) {
 		pr_warn("Unable to map DMAR\n");
@@ -663,9 +660,7 @@ dmar_find_matched_drhd_unit(struct pci_dev *dev)
 
 	rcu_read_lock();
 	for_each_drhd_unit(dmaru) {
-		drhd = container_of(dmaru->hdr,
-				    struct acpi_dmar_hardware_unit,
-				    header);
+		drhd = (struct acpi_dmar_hardware_unit *)dmaru->hdr;
 
 		if (dmaru->include_all &&
 		    drhd->segment == pci_domain_nr(dev->bus))
@@ -693,9 +688,7 @@ static void __init dmar_acpi_insert_dev_scope(u8 device_number,
 	struct acpi_dmar_pci_path *path;
 
 	for_each_drhd_unit(dmaru) {
-		drhd = container_of(dmaru->hdr,
-				    struct acpi_dmar_hardware_unit,
-				    header);
+		drhd = (struct acpi_dmar_hardware_unit *)dmaru->hdr;
 
 		for (scope = (void *)(drhd + 1);
 		     (unsigned long)scope < ((unsigned long)drhd) + drhd->header.length;
diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index e9bc929..5f6da7e 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -52,7 +52,6 @@ struct dmar_dev_scope {
 extern struct acpi_table_header *dmar_tbl;
 struct dmar_drhd_unit {
 	struct list_head list;		/* list of drhd units	*/
-	struct  acpi_dmar_header *hdr;	/* ACPI header		*/
 	u64	reg_base_addr;		/* register base address*/
 	struct	dmar_dev_scope *devices;/* target device array	*/
 	int	devices_cnt;		/* target device count	*/
@@ -60,6 +59,7 @@ struct dmar_drhd_unit {
 	u8	ignored:1; 		/* ignore drhd		*/
 	u8	include_all:1;
 	struct intel_iommu *iommu;
+	struct  acpi_dmar_header hdr[0];/* ACPI header		*/
 };
 
 struct dmar_pci_path {
-- 
1.7.9.5