On Mon, January 27, 2014 11:40, Karel Zak wrote: > On Mon, Jan 27, 2014 at 11:05:29AM +0100, Pali Rohár wrote: >> 2014-01-27 Karel Zak <kzak@xxxxxxxxxx>: >> > On Sun, Jan 26, 2014 at 10:24:39AM +0100, Milan Broz wrote: >> >> On 01/26/2014 02:40 AM, Pali Rohár wrote: >> >> > Hello, >> >> > >> >> > according to wikipedia [1] and other sites (e.g. [2]) MBR partition >> ID >> >> > for LUKS is E8. I tried to find GPT partition GUID for LUKS, but >> there >> >> > is nothing on wikipedia [3] nor google... So has LUKS already >> > >> > Frankly, who cares about partition types? >> > >> > IMHO partition types make sense in firmwares like UEFI to detect boot >> > partition (e.g. GPT system partition) or in special cases when you >> > want to mark a partition for a special purpose (e.g. /home). >> > >> > It's bad idea to use partition types for something else, especially >> > add to the partition table info about partition format (e.g. E8 for >> > LUKS). >> >> Why? > > because it duplicates information and result is fragile... Partition IDs can be very useful in hinting though. If I want to pull a component of a raid and move it, a list of partition IDs(or names) might ease my administration effort. In any case it would not harm to have additional information. > > It's always more robust to check /dev/sda3 then rely on partition type in > partition table. And slow. Checking all partitions for signatures can take quite some time, if we don't talk about a handfull of them. Hinting to look in these places first can increase the speed. And imagine there's not only say lvm and mdadm but other raid/lvm metadata tools with own signatures and on disk structure. A common indicator on partition level is meaningfull, as it is independent of a concrete implementation. > >> >> > It's nightmare to maintain something like this and I'm sure >> > that we don't want to maintain mkfs-like programs that modify >> > partition tables. >> > >> >> Of course, mkfs program should not modify partition table! Editing >> parittion table then it is up to system admin (if he using mkfs) or >> some high level partition program. > > but we want to have robust system and minimize complexity and > dependence on humans. So it's better to no depend on partition type by > default and use everywhere generic "data partition" than force people > to use special types for LUKS, LVM, swap, ... While it is more complex during setup/maintanance it eases (and possibly speeds up) operation. But that's just my POV. > >> >> > preferred/assigned GUID for GPT partition table? There is already >> GPT >> >> > GUID for linux data, raid, swap, lvm and home partitions (see [3]), >> so >> >> > I think that LUKS should have GUID too. >> > >> > All these are historical mistakes, I have doubts we want to contribute >> > to this nonsense. >> > >> > BTW, do you know what is the "official" list of the partition types >> > for MBR according to UEFI standard? It's Brouwer's (~aeb) web page >> [2]. >> > >> > IMHO it's pretty absurd situation when official standards have to link >> > random hobby web pages on Internet, because there is no official >> > authority that main such list... I think it obvious proof that >> > partition types for things like LIKS, swap, ... is unofficial junk. >> > >> >> In my opinion, if partition table (e.g GPT) support specifing >> partition label, uuid or partition type, why user/admin cannot use it >> (at least for his own usage)? > > Yes, for example partition UUID is excellent thing. I have nothing > against it. > > .. but we are talking about partition types for LUKS (swap, LVM, ..). There are good reasons though. Encrypted swap has no signature, thus you'd need a swap GUID, or use explicit PART UUID (not portable). So setting up encrypted swaps via GUID is straight forward, while all other means need a specific hard coding. I assume there's more good examples ... > >> I think its up to admin, if he want to >> use it or not. He can write own udev rules to export these information >> to system /dev/ or not. > > We already export information from PT to udev db and it's already used > in system (for example mount PARTUUID=). > > All my negative notes are about partition types only. > > Karel > > > -- > Karel Zak <kzak@xxxxxxxxxx> > http://karelzak.blogspot.com > _______________________________________________ > dm-crypt mailing list > dm-crypt@xxxxxxxx > http://www.saout.de/mailman/listinfo/dm-crypt > _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
