Re: [Qemu-devel] [PATCH v2 13/13] vvfat: change OEM name to 'MSWIN4.1'

From: "Hervé Poussineau" <hpoussin@reactos.org>
To: "Philippe Mathieu-Daudé" <f4bug@amsat.org>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	qemu-block@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v2 13/13] vvfat: change OEM name to 'MSWIN4.1'
Date: Tue, 23 May 2017 21:41:29 +0200	[thread overview]
Message-ID: <cf9a299e-1e02-6009-7579-3060874fc97e@reactos.org> (raw)
In-Reply-To: <75ccc442-1a32-bf36-3674-ec69ce944213@amsat.org>

Hi Philippe,

Le 23/05/2017 à 06:23, Philippe Mathieu-Daudé a écrit :
> Hi Hervé,
>
> On 05/22/2017 06:12 PM, Hervé Poussineau wrote:
>> According to specification:
>> "'MSWIN4.1' is the recommanded setting, because it is the setting least likely
>> to cause compatibility problems. If you want to put something else in here,
>> that is your option, but the result may be that some FAT drivers might not
>> recognize the volume."
>
> It also says "Typically this is some indication of what system formatted
> the volume."
>
> From https://technet.microsoft.com/en-us/library/cc976796.aspx:
>
> "Following the jump instruction is the 8-byte OEM ID, a string of characters that identifies the name and version number of the operating system that formatted the volume. To preserve compatibility
> with MS-DOS, Windows 2000 records "MSDOS5.0" in this field on FAT16 and FAT32 disks. On NTFS disks, Windows 2000 records "NTFS."
> You may also see the OEM ID "MSWIN4.0" on disks formatted by Windows 95 and "MSWIN4.1" on disks formatted by Windows 95 OSR2 and Windows 98. Windows 2000 does not use the OEM ID field in the boot
> sector except for verifying NTFS volumes."
>
> I'm curious which one is the most up-to-date, the specification v1.03 or a Windows 2000. Do you have an idea if there is more MSDOS/W2K vs W95/98 users? Hopefully W95 is a Long time no see to me.
>
> You think having "QEMU" OEM does more harm than good?

That's complicated. Indeed, OEM ID should be the name of the OS/tool which formatted the partition.
However, some FAT drivers take different paths according to OEM ID.
See for example:
https://jdebp.eu/FGA/volume-boot-block-oem-name-field.html
http://seasip.info./Misc/oemid.html

So, in my opinion, it should be better to stick to some specification for the whole FAT format, so we have a reference document to know if there is a bug in the code or not.
FAT specification 1.03 is dated December 6, 2000, while Windows 2000 has been released December 15, 1999, so both are around the same date.
FAT specification gives all details about all disk structures, so I think that's better to stick to what it says.

So to answer your question, and knowing the tricks played with OEM ID, I think that's better to use "MSWIN4.1" than "QEMU".

Regards,

Hervé

>
>>
>> Specification: "FAT: General overview of on-disk format" v1.03, page 9
>> Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
>> ---
>>  block/vvfat.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block/vvfat.c b/block/vvfat.c
>> index 53e8faa54c..1f7f46ecea 100644
>> --- a/block/vvfat.c
>> +++ b/block/vvfat.c
>> @@ -1024,7 +1024,7 @@ static int init_directories(BDRVVVFATState* s,
>>      bootsector->jump[0]=0xeb;
>>      bootsector->jump[1]=0x3e;
>>      bootsector->jump[2]=0x90;
>> -    memcpy(bootsector->name,"QEMU    ",8);
>> +    memcpy(bootsector->name, "MSWIN4.1", 8);
>>      bootsector->sector_size=cpu_to_le16(0x200);
>>      bootsector->sectors_per_cluster=s->sectors_per_cluster;
>>      bootsector->reserved_sectors=cpu_to_le16(1);
>>
>
> Regards,
>
> Phil.
>