linux-kernel - Re: [PATCH v2 2/3] genhd, efi: add efi partition metadata to hd

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Date:	Wed, 4 Aug 2010 09:44:46 -0500
From:	Will Drewry <wad@...omium.org>
To:	Karel Zak <kzak@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>, Jan Blunck <jblunck@...e.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH v2 2/3] genhd, efi: add efi partition metadata to 
	hd_structs

On Wed, Aug 4, 2010 at 4:00 AM, Karel Zak <kzak@...hat.com> wrote:
> On Tue, Aug 03, 2010 at 09:04:42PM -0500, Will Drewry wrote:
>> This change extends the partition_meta_info structure to
>> support EFI GPT-specific metadata and ensures that data
>> is copied in on partition scanning.
>
> Why do want to store GPT-specific data (efi_guid_t) to
> partition_meta_info? I think it would be better to use label and uuid
> in a generic format (e.g. string or u8 uuid[16]) -- then you don't
> have to use things like union, disklabel specific code to compare
> uuids, etc.  IMHO your current code is too complicated.
>
>> +             info = alloc_part_info(NULL);
>> +             if (!info) {
>> +                     printk(KERN_WARNING
>> +                            "unable to allocate memory for part->info\n");
>> +                     continue;
>> +             }
>> +             info->format = PARTITION_META_INFO_FORMAT_EFI;
>> +             memcpy(info->efi.uuid.b, ptes[i].unique_partition_guid.b,
>> +                     sizeof(info->efi.uuid.b));
>> +             memcpy(info->efi.type.b, ptes[i].partition_type_guid.b,
>> +                     sizeof(info->efi.type.b));
>
> why do you need to partition type?

For GPT, at least, the partition type isn't directly encoded anywhere
else and it can be vendor specific.  For instance, if a vendor wants
to make an auto-configuring, they could reserve a
VENDOR-ROOT-PRI0-PART-TYPE-GUID then easily create a mount path for
it.  Of course, that could easily be kludged by reusing a UUID.


>
>> +             memcpy(info->efi.label, ptes[i].partition_name,
>> +                     sizeof(info->efi.label));
>
> the partition name is in UTF8LE, is it correct to use it in raw
> format?

Since the type was partition specific, I left the data untouched. It
sounds like it'd be more useful to expose the data in a generic way
which would mean converting it, I guess?

>> +             state->parts[i + 1].info = info;
>>       }
>>       kfree(ptes);
>>       kfree(gpt);
>> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
>> index 7b6644a..beb98e3 100644
>> --- a/include/linux/genhd.h
>> +++ b/include/linux/genhd.h
>> @@ -91,11 +91,25 @@ struct disk_stats {
>>  enum partition_meta_info_format_t {
>>       /* Partition info format */
>>       PARTITION_META_INFO_FORMAT_NONE = 0,
>> +     PARTITION_META_INFO_FORMAT_EFI,
>> +     /* Place additional formats here. */
>> +     PARTITION_META_INFO_FORMAT_MAX,
>>  };
>>
>> +#ifdef CONFIG_EFI_PARTITION
>> +#include <linux/efi.h>
>> +#endif
>> +
>>  struct partition_meta_info {
>>       enum partition_meta_info_format_t format;
>>       union {
>> +#ifdef CONFIG_EFI_PARTITION
>> +             struct {
>> +                     efi_guid_t uuid;
>> +                     efi_guid_t type;
>> +                     efi_char16_t label[72 / sizeof(efi_char16_t)];
>> +             } efi;
>> +#endif
>>       };
>>  };
>>
>> --
>> 1.7.0.4
>>
>
> --
>  Karel Zak  <kzak@...hat.com>
>  http://karelzak.blogspot.com
>
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