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Date: Tue, 25 May 2021 15:00:37 +0300
From: Iurii Kamenev <damtev@...dex-team.ru>
To: Paolo Bonzini <pbonzini@...hat.com>,
Stefan Hajnoczi <stefanha@...hat.com>
Cc: "mst@...hat.com" <mst@...hat.com>,
"jasowang@...hat.com" <jasowang@...hat.com>,
"axboe@...nel.dk" <axboe@...nel.dk>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/1] virtio: disable partitions scanning for no partitions
block
Thanks for your remark. I guess it is possible, I will try to rewrite it
that way.
24.05.2021 22:41, Paolo Bonzini пишет:
> On 24/05/21 21:34, Юрий Каменев wrote:
>> Hi
>>
>> Is your goal to avoid accidentally detecting partitions because it's
>> confusing when that happens?
>>
>> The main goal is reducing the kernel start time. It might be use
>> useful in tiny systems that use, for example, squashfs images with
>> certainly no partitions. Disabling partitions scanning for these
>> images can save a few tens of milliseconds which can be a significant
>> acceleration for starting such systems.
>
> Perhaps that could be configured in the image, for example in the
> kernel command line?
>
> Paolo
>
>> 24.05.2021, 17:29, "Stefan Hajnoczi" <stefanha@...hat.com>:
>>
>> On Thu, May 20, 2021 at 04:39:08PM +0300, Yury Kamenev wrote:
>>
>> Hi,
>> Is there a VIRTIO spec change for the new VIRTIO_BLK_F_NO_PS feature
>> bit? Please send one:
>> https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback
>> <https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback>
>>
>> GENHD_FL_NO_PART_SCAN is not used much in other drivers. This
>> makes me
>> wonder if the same use case is addressed through other means with
>> SCSI,
>> NVMe, etc devices. Maybe Christoph or Jens can weigh in on whether
>> adding a bit to disable partition scanning for a virtio-blk fits
>> into
>> the big picture?
>>
>> Is your goal to avoid accidentally detecting partitions because it's
>> confusing when that happens?
>>
>> VIRTIO is currently undergoing auditing and changes to support
>> untrusted
>> devices. From that perspective adding a device feature bit to
>> disable
>> partition scanning does not help protect the guest from an untrusted
>> disk. The guest cannot trust the device, instead the guest itself
>> would
>> need to be configured to avoid partition scanning of untrusted
>> devices.
>>
>> Stefan
>>
>> Signed-off-by: Yury Kamenev <damtev@...dex-team.ru
>> <mailto:damtev@...dex-team.ru>>
>> ---
>> drivers/block/virtio_blk.c | 6 ++++++
>> include/uapi/linux/virtio_blk.h | 1 +
>> 2 files changed, 7 insertions(+)
>>
>> diff --git a/drivers/block/virtio_blk.c
>> b/drivers/block/virtio_blk.c
>> index b9fa3ef5b57c..17edcfee2208 100644
>> --- a/drivers/block/virtio_blk.c
>> +++ b/drivers/block/virtio_blk.c
>> @@ -799,6 +799,10 @@ static int virtblk_probe(struct
>> virtio_device *vdev)
>> vblk->disk->flags |= GENHD_FL_EXT_DEVT;
>> vblk->index = index;
>>
>> + /*Disable partitions scanning for no-partitions block*/
>>
>>
>> Formatting cleanup and rephrasing:
>>
>> /* Disable partition scanning for devices with no partitions */
>>
>> + if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PS))
>>
>>
>> I suggest user a more obvious name:
>>
>> VIRTIO_BLK_F_NO_PART_SCAN
>>
>> + vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
>> +
>> /* configure queue flush support */
>> virtblk_update_cache_mode(vdev);
>>
>> @@ -977,6 +981,7 @@ static unsigned int features_legacy[] = {
>> VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>> VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>> VIRTIO_BLK_F_CONFIG_WCE,
>> VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>> VIRTIO_BLK_F_WRITE_ZEROES,
>> + VIRTIO_BLK_F_NO_PS,
>> }
>> ;
>> static unsigned int features[] = {
>> @@ -984,6 +989,7 @@ static unsigned int features[] = {
>> VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
>> VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY,
>> VIRTIO_BLK_F_CONFIG_WCE,
>> VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD,
>> VIRTIO_BLK_F_WRITE_ZEROES,
>> + VIRTIO_BLK_F_NO_PS,
>> };
>>
>> static struct virtio_driver virtio_blk = {
>> diff --git a/include/uapi/linux/virtio_blk.h
>> b/include/uapi/linux/virtio_blk.h
>> index d888f013d9ff..f197d07afb05 100644
>> --- a/include/uapi/linux/virtio_blk.h
>> +++ b/include/uapi/linux/virtio_blk.h
>> @@ -40,6 +40,7 @@
>> #define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
>> #define VIRTIO_BLK_F_DISCARD 13 /* DISCARD is supported */
>> #define VIRTIO_BLK_F_WRITE_ZEROES 14 /* WRITE ZEROES is
>> supported */
>> +#define VIRTIO_BLK_F_NO_PS 16 /* No partitions */
>>
>> /* Legacy feature bits */
>> #ifndef VIRTIO_BLK_NO_LEGACY
>> --
>> 2.24.3 (Apple Git-128)
>>
>
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