linux-kernel - Re: [PATCH v7 1/8] efi: Export boot-services code and data as debugfs-blobs

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Message-ID: <340462a7-462a-3864-64bd-bdac5b428990@redhat.com>
Date:   Thu, 14 Nov 2019 12:31:18 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH v7 1/8] efi: Export boot-services code and data as
 debugfs-blobs

Hi,

On 14-10-2019 11:11, Luis Chamberlain wrote:
> On Fri, Oct 04, 2019 at 04:50:49PM +0200, Hans de Goede wrote:
>> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
>> index 8d3e778e988b..abba49c4c46d 100644
>> --- a/drivers/firmware/efi/efi.c
>> +++ b/drivers/firmware/efi/efi.c
>> @@ -314,6 +315,55 @@ static __init int efivar_ssdt_load(void)
>>   static inline int efivar_ssdt_load(void) { return 0; }
>>   #endif
>>   
>> +#ifdef CONFIG_DEBUG_FS
>> +
>> +#define EFI_DEBUGFS_MAX_BLOBS 32
>> +
>> +static struct debugfs_blob_wrapper debugfs_blob[EFI_DEBUGFS_MAX_BLOBS];
>> +
>> +static void __init efi_debugfs_init(void)
>> +{
>> +	struct dentry *efi_debugfs;
>> +	efi_memory_desc_t *md;
>> +	char name[32];
>> +	int type_count[EFI_BOOT_SERVICES_DATA + 1] = {};
>> +	int i = 0;
>> +
>> +	efi_debugfs = debugfs_create_dir("efi", NULL);
>> +	if (IS_ERR_OR_NULL(efi_debugfs))
>> +		return;
>> +
>> +	for_each_efi_memory_desc(md) {
>> +		switch (md->type) {
>> +		case EFI_BOOT_SERVICES_CODE:
>> +			snprintf(name, sizeof(name), "boot_services_code%d",
>> +				 type_count[md->type]++);
>> +			break;
>> +		case EFI_BOOT_SERVICES_DATA:
>> +			snprintf(name, sizeof(name), "boot_services_data%d",
>> +				 type_count[md->type]++);
>> +			break;
>> +		default:
>> +			continue;
>> +		}
>> +
>> +		debugfs_blob[i].size = md->num_pages << EFI_PAGE_SHIFT;
>> +		debugfs_blob[i].data = memremap(md->phys_addr,
>> +						debugfs_blob[i].size,
>> +						MEMREMAP_WB);
>> +		if (!debugfs_blob[i].data)
>> +			continue;
>> +
>> +		debugfs_create_blob(name, 0400, efi_debugfs, &debugfs_blob[i]);
>> +		i++;
>> +		if (i == EFI_DEBUGFS_MAX_BLOBS)
>> +			break;
> 
> Why do we silently ignore more entries ?

A valid remark, I agree that adding a pr_warn_once here would be good
I will do so for the next version.

> And could documentation be
> added for ways in which this could be used in practice?

I can write a little how to use this to get an embedded firmware,
I will add this to firmware/fallback-mechanisms.rst for the next
version.

Regards,

Hans