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[Qemu-devel] Re: [QEMU-KVM]: Megasas + TCM_Loop + SG_IO into Windows XP

From: Hannes Reinecke
Subject: [Qemu-devel] Re: [QEMU-KVM]: Megasas + TCM_Loop + SG_IO into Windows XP guests
Date: Tue, 18 May 2010 11:43:04 +0200
User-agent: Thunderbird (X11/20081227)

Nicholas A. Bellinger wrote:
> On Fri, 2010-05-14 at 02:42 -0700, Nicholas A. Bellinger wrote:
>> On Fri, 2010-05-14 at 09:22 +0200, Hannes Reinecke wrote:
>>> Nicholas A. Bellinger wrote:
>>>> Greetings Hannes and co,
>> <SNIP>
>>> Let's see if I can find some time working on the megasas emulation.
>>> Maybe I find something.
>>> Last time I checked it was with a Windows7 build, but I didn't do
>>> any real tests there. Basically just checking if the system boots up :-)
>> Nothing fancy just yet.  This is involving a normal NTFS filesystem
>> format on a small TCM/FILEIO LUN using scsi-generic and a userspace
>> FILEIO with scsi-disk.
>> This involves the XP guest waiting until the very last READ_10 once the
>> format has completed (eg: all WRITE and VERIFY CDBs complete with GOOD
>> status AFAICT) before announcing that mkfs.ntfs failed without any
>> helpful exception message (due to missing metadata of some sort I would
>> assume..?)
>> So perhaps dumping QEMU and TCM_Loop SCSI payloads to determine if any
>> correct blocks from megasas_handle_io() are actually making it out to
>> KVM host is going to be my next option.  ;)
> Greetings Hannes,
> So I spent some more time with XP guests this weekend, and I noticed two
> things immediately when using hw/lsi53c895a.c instead of hw/megasas.c
> with the same two TCM_Loop SAS LUNs via SG_IO from last week:
> 1) With lsi53c895a, XP guests are able to boot successfully w/ out the
> synchronous SG_IO hack that is currently required to get past the first
> 36-byte INQUIRY for megasas + XP SP2
> 2) With lsi53c895a, XP is able to successfully create and mount a NTFS
> filesystem, reboot, and read blocks appear to be functioning properly.
> FYI I have not run any 'write known pattern then read-back and compare
> blocks' data integrity tests from with in the XP guests just yet, but I
> am confident that TCM scatterlist -> se_mem_t mapping is working as
> expected on the KVM Host.
> Futhermore, after formatting a 5 GB TCM/FILEIO LUN with lsi53c895a, and
> then rebooting with megasas with the same two configured TCM_Loop SG_IO
> devices, it appears to be able to mount and read blocks successfully.
> Attempting to write new blocks on the mounted filesystem also appears to
> work to some degree, but throughput slows down to a crawl during XP
> guest buffer cache flush, which is likely attributed to the use of my
> quick SYNC SG_IO hack.
> So it appears that there are two seperate issues here, and AFAICT they
> both look to be XP and megasas specific.  For #2, it may be something
> about the format of the incoming scatterlists generated during XP's
> mkfs.ntfs that is causing some issues.  While watching output during fs
> creation, I noticed the following WRITE_10s with a starting 4088 byte
> scatterlist and a trailing 8 byte scatterlist:
> megasas: writel mmio 40: 2b0b003
> megasas: Found mapped frame 2 context 82b0b000 pa 2b0b000
> megasas: Enqueue frame context 82b0b000 tail 493 busy 1
> megasas: LD SCSI dev 2 lun 0 sdev 0xdc0230 xfer 16384
> scsi-generic: Using cur_addr: 0x000000000ff6c008 cur_len: 0x0000000000000ff8
> scsi-generic: Adding iovec for mem: 0x7f1783b96008 len: 0x0000000000000ff8
> scsi-generic: Using cur_addr: 0x000000000fd6e000 cur_len: 0x0000000000001000
> scsi-generic: Adding iovec for mem: 0x7f1783998000 len: 0x0000000000001000
> scsi-generic: Using cur_addr: 0x000000000fe2f000 cur_len: 0x0000000000001000
> scsi-generic: Adding iovec for mem: 0x7f1783a59000 len: 0x0000000000001000
> scsi-generic: Using cur_addr: 0x000000000fdf0000 cur_len: 0x0000000000001000
> scsi-generic: Adding iovec for mem: 0x7f1783a1a000 len: 0x0000000000001000
> scsi-generic: Using cur_addr: 0x000000000fded000 cur_len: 0x0000000000000008
> scsi-generic: Adding iovec for mem: 0x7f1783a17000 len: 0x0000000000000008
> scsi-generic: execute IOV: iovec_count: 5, dxferp: 0xd92420, dxfer_len: 16384
> scsi-generic: -----------------------> Issuing SG_IO CDB len 10: 0x2a 00 00 
> 00 fa be 00 00 20 00 
> scsi-generic: scsi_write_complete() ret = 0
> scsi-generic: Command complete 0x0xd922c0 tag=0x82b0b000 status=0
> megasas: LD SCSI req 0xd922c0 cmd 0xda92c0 lun 0xdc0230 finished with status 
> 0 len 16384
> megasas: Complete frame context 82b0b000 tail 493 busy 0 doorbell 0
> Also, the final READ_10 that produces the 'could not create filesystem'
> exception is for LBA 63 and XP looking for the first FS blocks after
> GPT.
> Could there be some breakage in megasas with a length < PAGE_SIZE for
> the scatterlist..?    As lsi53c895a seems to work OK for this case, is
> there something about the logic of parsing the incoming struct
> scatterlists that is different between the two HBA drivers..?  AFAICT
> both are using Gerd's common code in hw/scsi-bus.c, unless there is
> something about megasas_map_sgl() that is causing issues with the
> above..?

The usual disclaimer here: I'm less than happy with the current SCSI disk 
Currently we have the two options:
- Using 'scsi-disk', which will _emulate_ a SCSI disk internally, but allow to 
  asynchronous I/O using normal read/write syscalls
- Using 'scsi-generic', which will allow you to pass-through any SCSI device, 
  disallow asynchronous I/O and requires you to use the SG_IO interface.
The latter also implies that the host will mark _all_ I/O commands as 
so the code path within the kernel is quite different from those taken by I/Os
coming in via the 'scsi-disk' emulation.
Guess it's time to have a 'scsi-passthrough' device ...

Other than that: Think we have to investigate.
If you could send me a quite setup guide on how to configure TCM_Loop for an
existing device I'd give it a go ...


Dr. Hannes Reinecke                   zSeries & Storage
address@hidden                        +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)

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