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Re: [Qemu-devel] [PATCH] Reject virtio-scsi configurations with logical
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] Reject virtio-scsi configurations with logical block size > physical block size |
Date: |
Wed, 18 Oct 2017 11:53:36 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 |
On 16/10/2017 22:17, Mark Kanda wrote:
> With virtio-scsi, logical block size should never be larger than
> physical block size. From an ATA/SCSI perspective, it makes no sense
> to have the logical block size greater than the physical block size,
> and it cannot even be effectively expressed in the command set. The
> whole point of adding the physical block size to the ATA/SCSI command
> set was to communicate a desire for a larger block size (than logical),
> while maintaining backwards compatibility with legacy 512 byte block
> size.
>
> This was found by setting logical_block_size > physical_block_size in
> the QEMU command line, and discovering that it confuses Windows VMs -
> fsutil reports both physical and logical block sizes are equal to the
> logical size.
It doesn't confuse Windows VMs; physical block size is expressed as a
number n such that physical_block_size = 2^n * logical_block_size. So
if you specify an invalid configuration (which as you say "cannot be
expressed" in SBC) all QEMU can do is set n=0.
fsutil therefore prints exactly what QEMU says in READ CAPACITY. :)
I've adjusted a little bit the commit message and queued the patch, thanks!
Paolo
> Example QEMU option:
>
> -device scsi-hd,drive=drive-scsi0,id=disk1,bus=scsi.0,
> physical_block_size=512,logical_block_size=4096
>
> Windows Server 2012 R2 VM:
>
> C:\Users\Administrator>fsutil fsinfo ntfsinfo F:
> ...
> Bytes Per Sector : 4096
> Bytes Per Physical Sector : 4096
> Bytes Per Cluster : 4096
> Bytes Per FileRecord Segment : 4096
> ...
>
> Signed-off-by: Mark Kanda <address@hidden>
> Reviewed-by: Konrad Rzeszutek Wilk <address@hidden>
> Reviewed-by: Martin K. Petersen <address@hidden>
> ---
> hw/scsi/scsi-disk.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
> index 6e841fb..2a4f8c5 100644
> --- a/hw/scsi/scsi-disk.c
> +++ b/hw/scsi/scsi-disk.c
> @@ -2329,6 +2329,14 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
>
> blkconf_serial(&s->qdev.conf, &s->serial);
> blkconf_blocksizes(&s->qdev.conf);
> +
> + if (s->qdev.conf.logical_block_size >
> + s->qdev.conf.physical_block_size) {
> + error_setg(errp,
> + "logical_block_size > physical_block_size not supported");
> + return;
> + }
> +
> if (dev->type == TYPE_DISK) {
> blkconf_geometry(&dev->conf, NULL, 65535, 255, 255, &err);
> if (err) {
>