Avi Kivity wrote:
On 06/15/2009 04:20 PM, Anthony Liguori wrote:
It's not at all that simple. SCSI has a hierarchical address
mechanism with 0-7 targets but then potentially multiple LUNs per
target. Today, we always emulate a single LUN per target but if we
ever wanted to support more than 7 disks on a SCSI controller, we
would have to add multiple LUN support too. So the current linear
unit= parameter is actually pretty broken for SCSI.
Well, another level in the hierarchy, but I don't think it materially
changes things.
Depends on whether you expect to say index=0,lun=3 or index=3. If you
mean the later, then it's quite conceivable that each target supports
less than the maximum number of LUNs. This makes things pretty
confusing to the user because they have to know that in the current
implementation, index=0 is valid, index=1 isn't, but index=8 is.
No, I meant drive file=foo.img,bus=3. If that doesn't seem obvious
what it should do to you that's because it isn't at all obvious :-)
It ends up skipping a predefined number of locations in the drive
table. This is pretty broken fundamentally because it assumes
controllers always support a fixed number of devices. Nothing really
respects bus_id though so in practice, I assume it's almost
universally broken.
Isn't the drive table something totally internal? And how does bus=
relate to it?
The reality of unit=X,bus=Y,if=Z is that they expand to:
drive_table_index=Y*max_devs[Z] + X
Whereas max_devs = {"ide":4, "scsi": 7, *:0}
How drive_table_index is interpreted is "if" specific. For if=scsi,
each lsi device gets a base drive table index that starts at bus_index *
7. For virtio, the first empty spot in drive_table results in no more
drives being created.
It's broken by design.
Regards,
Anthony Liguori
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