On 01/15/2015 10:43 AM, Daniel P. Berrange wrote:
>>
>> I looked through some history and didn't see anywhere that supplied name
>> must match partition name was enforced, but there's a lot of code motion
>> and new features that may cloud the history. Perhaps it's the assumption
>> true in so many other pools that 'name' is what was used to create the
>> file, directory, lv, etc. There is code that fills in the name if not
>> provided with the partition name (which occurs after Refresh, reload,
>> restart).
>
> Looking back some more, it seems I did not ever enforce it - I just
> left it as something users had to set the "right way" by convention.
> ie I just expected callers to always use the right "sdaNNN" value
>
So then should this morph into a fix which causes a failure if a
matching name wasn't passed? Or should we "be nice", "fix it" to
whatever mkpart generates, and not fail?
The check could be done in virStorageBackendDiskMakeDataVol which
refresh, reload, restart already uses in order to assign partition name
(eg, tmp) to vol->name.
The downside of the fail case in that code is we'll need to delete the
partition that just created - something that isn't already done in any
of the failure cases. Trying to compare the name prior to creation
against the assumed next partition # means we'll need to create an
algorithm that finds all the partition numbers and figures out what the
next one will be. They're not necessarily "in order".
As for the target.format (<target...> <format type='linux'> </target>)
I'm inclined to just let it be. Although it does have one use - since
"extended" is a valid virStorageVolFormatDisk value, one could create an
extended partition before all the primary ones are created.
John
>> I'm not quite sure how one could enforce a name given that parted
>> creates the partition name. One would have to know the device name of
>> the pool and the numerical sequence that parted would use (easy perhaps
>> know that perhaps partitions 1 & 2 exist that 3 will be next). However,
>> there's not necessarily a guarantee of that is there?
>
> For MS-DOS partition tables the partition entry number directly
> corresponds to the device name suffix. eg partition 3 corresponds
> to /dev/sda3 always and is happy to be sparse. eg if you create
> 3 partitions and then delete partition 2, you'll end up with
> /dev/sda1 and /dev/sda3
>
> Testing with parted the same seems to be true of GPT tables too.
>
>> Reading the libvirt docs - the implication is that the volume "<name>"
>> must only be unique across the pool, so the following is "valid":
>>
>> virsh vol-create-as disk-pool vol-linux --format linux 1G
>>
>> So without assuming/describing the naming scheme of the underlying
>> parted how do we enforce that the name (vol-linux) is the same as what
>> parted generates? Or how do we enforce that the name provided ends up
>> being the same as the partition created? It's kind of a chicken/egg issue.
>
> Well with disk partitions we know the device name
>
> eg the pool knows we're operating on '/dev/sda', so when we create
> it can we validate that the volume name is '/dev/sdaNNN' by kjust
> doing a string prefix match
>
>> Not much is done with the target.format in the backend even though it's
>> described as providing the "partition type". When not provided on the
>> command line like above it defaults to 'none'. Other than for dos label
>> pools that would need to have extended partition before creating a
>> logical partition, there's not much "use" for the field other than to
>> perhaps store "something" for "someone" (until refresh, reload, restart
>> loses it).
>
> When you create a partition you can specify filesystem type for that
> partition, even though it is somewhat redundant as it is not directly
> connected to the filesystem that you actually mkfs. eg this list of
> types from fdisk
>
> Command (m for help): l
>
> 0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris
> 1 FAT12 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT-
> 2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT-
> 3 XENIX usr 3c PartitionMagic 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
> 4 FAT16 <32M 40 Venix 80286 85 Linux extended c7 Syrinx
> 5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data
> 6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / .
> 7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility
> 8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt
> 9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access
> a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O
> b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor
> c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi eb BeOS fs
> e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD ee GPT
> f W95 Ext'd (LBA) 54 OnTrackDM6 a6 OpenBSD ef EFI (FAT-12/16/
> 10 OPUS 55 EZ-Drive a7 NeXTSTEP f0 Linux/PA-RISC b
> 11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f1 SpeedStor
> 12 Compaq diagnost 5c Priam Edisk a9 NetBSD f4 SpeedStor
> 14 Hidden FAT16 <3 61 SpeedStor ab Darwin boot f2 DOS secondary
> 16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ fb VMware VMFS
> 17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
> 18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
> 1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
> 1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
> 1e Hidden W95 FAT1 80 Old Minix
>
>
>
> I did make a start on defining this for the XML:
>
> /*
> * XXX: these are basically partition types.
> *
> * fdisk has a bazillion partition ID types parted has
> * practically none, and splits the * info across 3
> * different attributes.
> *
> * So this is a semi-generic set
> */
> typedef enum {
> VIR_STORAGE_VOL_DISK_NONE = 0,
> VIR_STORAGE_VOL_DISK_LINUX,
> VIR_STORAGE_VOL_DISK_FAT16,
> VIR_STORAGE_VOL_DISK_FAT32,
> VIR_STORAGE_VOL_DISK_LINUX_SWAP,
> VIR_STORAGE_VOL_DISK_LINUX_LVM,
> VIR_STORAGE_VOL_DISK_LINUX_RAID,
> VIR_STORAGE_VOL_DISK_EXTENDED,
> VIR_STORAGE_VOL_DISK_LAST,
> } virStorageVolFormatDisk;
> VIR_ENUM_DECL(virStorageVolFormatDisk)
>
>
> but then storage_backend_disk never made use of this information
>
> I'm not sure how important this is, but if we do want to make use
> of 'format' for the disk pool, this partition types are what I'd
> map it too.
>
> Regards,
> Daniel
>
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