[PATCH] x86/xen: populate boot_params with EDD data

[PATCH] x86/xen: populate boot_params with EDD data

[David Vrabel]

From: David Vrabel <david.vrabel@citrix.com>

During early setup of a dom0 kernel, populate boot_params with the
Enhanced Disk Drive (EDD) and MBR signature data.  This makes
information on the BIOS boot device available in /sys/firmware/edd/.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/xen/enlighten.c |   57 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8e1c7b..857d3bc 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,6 +31,7 @@
 #include <linux/pci.h>
 #include <linux/gfp.h>
 #include <linux/memblock.h>
+#include <linux/edd.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -1306,6 +1307,60 @@ static const struct machine_ops xen_machine_ops __initconst = {
 	.emergency_restart = xen_emergency_restart,
 };
 
+#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
+static void __init load_edd(void)
+{
+	struct xen_platform_op op;
+	struct edd_info *edd_info;
+	u32 *mbr_signature;
+	unsigned nr;
+	int ret;
+
+	edd_info = boot_params.eddbuf;
+	mbr_signature = boot_params.edd_mbr_sig_buffer;
+
+	op.cmd = XENPF_firmware_info;
+
+	op.u.firmware_info.type = XEN_FW_DISK_INFO;
+	for (nr = 0; nr < EDDMAXNR; nr++) {
+		struct edd_info *info = edd_info + nr;
+
+		op.u.firmware_info.index = nr;
+		info->params.length = sizeof(info->params);
+		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
+				     &info->params);
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+
+#define C(x) info->x = op.u.firmware_info.u.disk_info.x
+		C(device);
+		C(version);
+		C(interface_support);
+		C(legacy_max_cylinder);
+		C(legacy_max_head);
+		C(legacy_sectors_per_track);
+#undef C
+	}
+	boot_params.eddbuf_entries = nr;
+
+	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
+	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
+		op.u.firmware_info.index = nr;
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
+	}
+	boot_params.edd_mbr_sig_buf_entries = nr;
+}
+#else
+static inline void __init load_edd(void)
+{
+}
+#endif
+
+
 /*
  * Set up the GDT and segment registers for -fstack-protector.  Until
  * we do this, we have to be careful not to call any stack-protected
@@ -1508,6 +1563,8 @@ asmlinkage void __init xen_start_kernel(void)
 		/* Avoid searching for BIOS MP tables */
 		x86_init.mpparse.find_smp_config = x86_init_noop;
 		x86_init.mpparse.get_smp_config = x86_init_uint_noop;
+
+		load_edd();
 	}
 #ifdef CONFIG_PCI
 	/* PCI BIOS service won't work from a PV guest. */
-- 
1.7.2.5

Re: [PATCH] x86/xen: populate boot_params with EDD data

[Jan Beulich]

>>> On 03.04.13 at 13:10, David Vrabel <david.vrabel@citrix.com> wrote:
> @@ -1306,6 +1307,60 @@ static const struct machine_ops xen_machine_ops __initconst = {
>  	.emergency_restart = xen_emergency_restart,
>  };
>  
> +#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)

This is

#if IS_ENABLED(CONFIG_EDD)

nowadays.

> +static void __init load_edd(void)
> +{
> +	struct xen_platform_op op;
> +	struct edd_info *edd_info;
> +	u32 *mbr_signature;
> +	unsigned nr;
> +	int ret;
> +
> +	edd_info = boot_params.eddbuf;
> +	mbr_signature = boot_params.edd_mbr_sig_buffer;
> +
> +	op.cmd = XENPF_firmware_info;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_INFO;
> +	for (nr = 0; nr < EDDMAXNR; nr++) {
> +		struct edd_info *info = edd_info + nr;
> +
> +		op.u.firmware_info.index = nr;
> +		info->params.length = sizeof(info->params);
> +		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
> +				     &info->params);
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +
> +#define C(x) info->x = op.u.firmware_info.u.disk_info.x
> +		C(device);
> +		C(version);
> +		C(interface_support);
> +		C(legacy_max_cylinder);
> +		C(legacy_max_head);
> +		C(legacy_sectors_per_track);
> +#undef C
> +	}
> +	boot_params.eddbuf_entries = nr;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
> +	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
> +		op.u.firmware_info.index = nr;
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
> +	}
> +	boot_params.edd_mbr_sig_buf_entries = nr;
> +}
> +#else
> +static inline void __init load_edd(void)
> +{
> +}
> +#endif

And if you put the conditionals inside the curly braces, you can
avoid the else portion here altogether.

Jan

Re: [PATCH] x86/xen: populate boot_params with EDD data

[David Vrabel]

On 03/04/13 13:47, Jan Beulich wrote:
>>>> On 03.04.13 at 13:10, David Vrabel <david.vrabel@citrix.com> wrote:
>> +}
>> +#else
>> +static inline void __init load_edd(void)
>> +{
>> +}
>> +#endif
> 
> And if you put the conditionals inside the curly braces, you can
> avoid the else portion here altogether.

I thought the #if around the whole function was the standard pattern.
Konrad, what's your opinion here?

David

Re: [PATCH] x86/xen: populate boot_params with EDD data

[Konrad Rzeszutek Wilk]

On Wed, Apr 03, 2013 at 01:49:16PM +0100, David Vrabel wrote:
> On 03/04/13 13:47, Jan Beulich wrote:
> >>>> On 03.04.13 at 13:10, David Vrabel <david.vrabel@citrix.com> wrote:
> >> +}
> >> +#else
> >> +static inline void __init load_edd(void)
> >> +{
> >> +}
> >> +#endif
> > 
> > And if you put the conditionals inside the curly braces, you can
> > avoid the else portion here altogether.
> 
> I thought the #if around the whole function was the standard pattern.
> Konrad, what's your opinion here?

That is the way to do it in the header files.

You are not doing this in a header, I would go with what
Jan suggested and just do the #ifdef CONFIG_EDD.. inside the function.

Also just for completness, lets call the function 'xen_load_edd'

> 
> David
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
> 

[PATCHv3] x86/xen: populate boot_params with EDD data

[David Vrabel]

From: David Vrabel <david.vrabel@citrix.com>

During early setup of a dom0 kernel, populate boot_params with the
Enhanced Disk Drive (EDD) and MBR signature data.  This makes
information on the BIOS boot device available in /sys/firmware/edd/.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
v3:
- load_edd() -> xen_boot_params_init_edd()
v2:
- use IS_ENABLED()
- #if in the function looks more readable
---
 arch/x86/xen/enlighten.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8e1c7b..47d3243 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,6 +31,7 @@
 #include <linux/pci.h>
 #include <linux/gfp.h>
 #include <linux/memblock.h>
+#include <linux/edd.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -1306,6 +1307,55 @@ static const struct machine_ops xen_machine_ops __initconst = {
 	.emergency_restart = xen_emergency_restart,
 };
 
+static void __init xen_boot_params_init_edd(void)
+{
+#if IS_ENABLED(CONFIG_EDD)
+	struct xen_platform_op op;
+	struct edd_info *edd_info;
+	u32 *mbr_signature;
+	unsigned nr;
+	int ret;
+
+	edd_info = boot_params.eddbuf;
+	mbr_signature = boot_params.edd_mbr_sig_buffer;
+
+	op.cmd = XENPF_firmware_info;
+
+	op.u.firmware_info.type = XEN_FW_DISK_INFO;
+	for (nr = 0; nr < EDDMAXNR; nr++) {
+		struct edd_info *info = edd_info + nr;
+
+		op.u.firmware_info.index = nr;
+		info->params.length = sizeof(info->params);
+		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
+				     &info->params);
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+
+#define C(x) info->x = op.u.firmware_info.u.disk_info.x
+		C(device);
+		C(version);
+		C(interface_support);
+		C(legacy_max_cylinder);
+		C(legacy_max_head);
+		C(legacy_sectors_per_track);
+#undef C
+	}
+	boot_params.eddbuf_entries = nr;
+
+	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
+	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
+		op.u.firmware_info.index = nr;
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
+	}
+	boot_params.edd_mbr_sig_buf_entries = nr;
+#endif
+}
+
 /*
  * Set up the GDT and segment registers for -fstack-protector.  Until
  * we do this, we have to be careful not to call any stack-protected
@@ -1508,6 +1558,8 @@ asmlinkage void __init xen_start_kernel(void)
 		/* Avoid searching for BIOS MP tables */
 		x86_init.mpparse.find_smp_config = x86_init_noop;
 		x86_init.mpparse.get_smp_config = x86_init_uint_noop;
+
+		xen_boot_params_init_edd();
 	}
 #ifdef CONFIG_PCI
 	/* PCI BIOS service won't work from a PV guest. */
-- 
1.7.2.5

[PATCHv2] x86/xen: populate boot_params with EDD data

[David Vrabel]

From: David Vrabel <david.vrabel@citrix.com>

During early setup of a dom0 kernel, populate boot_params with the
Enhanced Disk Drive (EDD) and MBR signature data.  This makes
information on the BIOS boot device available in /sys/firmware/edd/.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
v2:
- use IS_ENABLED()
- #if in the function looks more readable
---
 arch/x86/xen/enlighten.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8e1c7b..dfe5422 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,6 +31,7 @@
 #include <linux/pci.h>
 #include <linux/gfp.h>
 #include <linux/memblock.h>
+#include <linux/edd.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -1306,6 +1307,55 @@ static const struct machine_ops xen_machine_ops __initconst = {
 	.emergency_restart = xen_emergency_restart,
 };
 
+static void __init load_edd(void)
+{
+#if IS_ENABLED(CONFIG_EDD)
+	struct xen_platform_op op;
+	struct edd_info *edd_info;
+	u32 *mbr_signature;
+	unsigned nr;
+	int ret;
+
+	edd_info = boot_params.eddbuf;
+	mbr_signature = boot_params.edd_mbr_sig_buffer;
+
+	op.cmd = XENPF_firmware_info;
+
+	op.u.firmware_info.type = XEN_FW_DISK_INFO;
+	for (nr = 0; nr < EDDMAXNR; nr++) {
+		struct edd_info *info = edd_info + nr;
+
+		op.u.firmware_info.index = nr;
+		info->params.length = sizeof(info->params);
+		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
+				     &info->params);
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+
+#define C(x) info->x = op.u.firmware_info.u.disk_info.x
+		C(device);
+		C(version);
+		C(interface_support);
+		C(legacy_max_cylinder);
+		C(legacy_max_head);
+		C(legacy_sectors_per_track);
+#undef C
+	}
+	boot_params.eddbuf_entries = nr;
+
+	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
+	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
+		op.u.firmware_info.index = nr;
+		ret = HYPERVISOR_dom0_op(&op);
+		if (ret)
+			break;
+		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
+	}
+	boot_params.edd_mbr_sig_buf_entries = nr;
+#endif
+}
+
 /*
  * Set up the GDT and segment registers for -fstack-protector.  Until
  * we do this, we have to be careful not to call any stack-protected
@@ -1508,6 +1558,8 @@ asmlinkage void __init xen_start_kernel(void)
 		/* Avoid searching for BIOS MP tables */
 		x86_init.mpparse.find_smp_config = x86_init_noop;
 		x86_init.mpparse.get_smp_config = x86_init_uint_noop;
+
+		load_edd();
 	}
 #ifdef CONFIG_PCI
 	/* PCI BIOS service won't work from a PV guest. */
-- 
1.7.2.5

Re: [PATCHv2] x86/xen: populate boot_params with EDD data

[Jan Beulich]

>>> On 03.04.13 at 15:29, David Vrabel <david.vrabel@citrix.com> wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> During early setup of a dom0 kernel, populate boot_params with the
> Enhanced Disk Drive (EDD) and MBR signature data.  This makes
> information on the BIOS boot device available in /sys/firmware/edd/.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -31,6 +31,7 @@
>  #include <linux/pci.h>
>  #include <linux/gfp.h>
>  #include <linux/memblock.h>
> +#include <linux/edd.h>
>  
>  #include <xen/xen.h>
>  #include <xen/events.h>
> @@ -1306,6 +1307,55 @@ static const struct machine_ops xen_machine_ops 
> __initconst = {
>  	.emergency_restart = xen_emergency_restart,
>  };
>  
> +static void __init load_edd(void)
> +{
> +#if IS_ENABLED(CONFIG_EDD)
> +	struct xen_platform_op op;
> +	struct edd_info *edd_info;
> +	u32 *mbr_signature;
> +	unsigned nr;
> +	int ret;
> +
> +	edd_info = boot_params.eddbuf;
> +	mbr_signature = boot_params.edd_mbr_sig_buffer;
> +
> +	op.cmd = XENPF_firmware_info;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_INFO;
> +	for (nr = 0; nr < EDDMAXNR; nr++) {
> +		struct edd_info *info = edd_info + nr;
> +
> +		op.u.firmware_info.index = nr;
> +		info->params.length = sizeof(info->params);
> +		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
> +				     &info->params);
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +
> +#define C(x) info->x = op.u.firmware_info.u.disk_info.x
> +		C(device);
> +		C(version);
> +		C(interface_support);
> +		C(legacy_max_cylinder);
> +		C(legacy_max_head);
> +		C(legacy_sectors_per_track);
> +#undef C
> +	}
> +	boot_params.eddbuf_entries = nr;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
> +	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
> +		op.u.firmware_info.index = nr;
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
> +	}
> +	boot_params.edd_mbr_sig_buf_entries = nr;
> +#endif
> +}
> +
>  /*
>   * Set up the GDT and segment registers for -fstack-protector.  Until
>   * we do this, we have to be careful not to call any stack-protected
> @@ -1508,6 +1558,8 @@ asmlinkage void __init xen_start_kernel(void)
>  		/* Avoid searching for BIOS MP tables */
>  		x86_init.mpparse.find_smp_config = x86_init_noop;
>  		x86_init.mpparse.get_smp_config = x86_init_uint_noop;
> +
> +		load_edd();
>  	}
>  #ifdef CONFIG_PCI
>  	/* PCI BIOS service won't work from a PV guest. */

Re: [PATCH] x86/xen: populate boot_params with EDD data

[Konrad Rzeszutek Wilk]

On Wed, Apr 03, 2013 at 12:10:49PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> During early setup of a dom0 kernel, populate boot_params with the
> Enhanced Disk Drive (EDD) and MBR signature data.  This makes
> information on the BIOS boot device available in /sys/firmware/edd/.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  arch/x86/xen/enlighten.c |   57 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 57 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index c8e1c7b..857d3bc 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -31,6 +31,7 @@
>  #include <linux/pci.h>
>  #include <linux/gfp.h>
>  #include <linux/memblock.h>
> +#include <linux/edd.h>
>  
>  #include <xen/xen.h>
>  #include <xen/events.h>
> @@ -1306,6 +1307,60 @@ static const struct machine_ops xen_machine_ops __initconst = {
>  	.emergency_restart = xen_emergency_restart,
>  };
>  
> +#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
> +static void __init load_edd(void)
> +{
> +	struct xen_platform_op op;
> +	struct edd_info *edd_info;
> +	u32 *mbr_signature;
> +	unsigned nr;
> +	int ret;
> +
> +	edd_info = boot_params.eddbuf;
> +	mbr_signature = boot_params.edd_mbr_sig_buffer;
> +
> +	op.cmd = XENPF_firmware_info;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_INFO;
> +	for (nr = 0; nr < EDDMAXNR; nr++) {
> +		struct edd_info *info = edd_info + nr;
> +
> +		op.u.firmware_info.index = nr;
> +		info->params.length = sizeof(info->params);
> +		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
> +				     &info->params);
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +
> +#define C(x) info->x = op.u.firmware_info.u.disk_info.x
> +		C(device);
> +		C(version);
> +		C(interface_support);
> +		C(legacy_max_cylinder);
> +		C(legacy_max_head);
> +		C(legacy_sectors_per_track);
> +#undef C
> +	}
> +	boot_params.eddbuf_entries = nr;
> +
> +	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
> +	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
> +		op.u.firmware_info.index = nr;
> +		ret = HYPERVISOR_dom0_op(&op);
> +		if (ret)
> +			break;
> +		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
> +	}
> +	boot_params.edd_mbr_sig_buf_entries = nr;

If those two loops end up terminating at different spots (say first
one ends at nr=1, and the second at nr=5), is that going to present
a problem?

Should we have some form of 'min(nr_earlier, nr)' to clamp down in
case of weird oddities?

> +}
> +#else
> +static inline void __init load_edd(void)
> +{
> +}
> +#endif
> +
> +
>  /*
>   * Set up the GDT and segment registers for -fstack-protector.  Until
>   * we do this, we have to be careful not to call any stack-protected
> @@ -1508,6 +1563,8 @@ asmlinkage void __init xen_start_kernel(void)
>  		/* Avoid searching for BIOS MP tables */
>  		x86_init.mpparse.find_smp_config = x86_init_noop;
>  		x86_init.mpparse.get_smp_config = x86_init_uint_noop;
> +
> +		load_edd();
>  	}
>  #ifdef CONFIG_PCI
>  	/* PCI BIOS service won't work from a PV guest. */
> -- 
> 1.7.2.5
> 

Re: [PATCH] x86/xen: populate boot_params with EDD data

[David Vrabel]

On 03/04/13 15:53, Konrad Rzeszutek Wilk wrote:
> On Wed, Apr 03, 2013 at 12:10:49PM +0100, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> During early setup of a dom0 kernel, populate boot_params with the
>> Enhanced Disk Drive (EDD) and MBR signature data.  This makes
>> information on the BIOS boot device available in /sys/firmware/edd/.
[...]
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -1306,6 +1307,60 @@ static const struct machine_ops xen_machine_ops __initconst = {
>>  	.emergency_restart = xen_emergency_restart,
>>  };
>>  
>> +#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
>> +static void __init load_edd(void)
>> +{
>> +	struct xen_platform_op op;
>> +	struct edd_info *edd_info;
>> +	u32 *mbr_signature;
>> +	unsigned nr;
>> +	int ret;
>> +
>> +	edd_info = boot_params.eddbuf;
>> +	mbr_signature = boot_params.edd_mbr_sig_buffer;
>> +
>> +	op.cmd = XENPF_firmware_info;
>> +
>> +	op.u.firmware_info.type = XEN_FW_DISK_INFO;
>> +	for (nr = 0; nr < EDDMAXNR; nr++) {
>> +		struct edd_info *info = edd_info + nr;
>> +
>> +		op.u.firmware_info.index = nr;
>> +		info->params.length = sizeof(info->params);
>> +		set_xen_guest_handle(op.u.firmware_info.u.disk_info.edd_params,
>> +				     &info->params);
>> +		ret = HYPERVISOR_dom0_op(&op);
>> +		if (ret)
>> +			break;
>> +
>> +#define C(x) info->x = op.u.firmware_info.u.disk_info.x
>> +		C(device);
>> +		C(version);
>> +		C(interface_support);
>> +		C(legacy_max_cylinder);
>> +		C(legacy_max_head);
>> +		C(legacy_sectors_per_track);
>> +#undef C
>> +	}
>> +	boot_params.eddbuf_entries = nr;
>> +
>> +	op.u.firmware_info.type = XEN_FW_DISK_MBR_SIGNATURE;
>> +	for (nr = 0; nr < EDD_MBR_SIG_MAX; nr++) {
>> +		op.u.firmware_info.index = nr;
>> +		ret = HYPERVISOR_dom0_op(&op);
>> +		if (ret)
>> +			break;
>> +		mbr_signature[nr] = op.u.firmware_info.u.disk_mbr_signature.mbr_signature;
>> +	}
>> +	boot_params.edd_mbr_sig_buf_entries = nr;
> 
> If those two loops end up terminating at different spots (say first
> one ends at nr=1, and the second at nr=5), is that going to present
> a problem?
> 
> Should we have some form of 'min(nr_earlier, nr)' to clamp down in
> case of weird oddities?

The edd firmware driver looks to correctly handle this -- it will only
show attributes for things that exist.

David