[PATCH] xen-blkfront: don't make discard-alignment mandatory

[PATCH] xen-blkfront: don't make discard-alignment mandatory

[Roger Pau Monne]

Don't require the discard-alignment xenstore node to be present in
order to correctly setup the feature. This can happen with versions of
QEMU that only write the discard-granularity but not the
discard-alignment node.

Assume discard-alignment is 0 if not present. While there also fix the
logic to not enable the discard feature if discard-granularity is not
present.

Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: xen-devel@lists.xenproject.org
Cc: linux-block@vger.kernel.org
Cc: Arthur Borsboom <arthurborsboom@gmail.com>
---
 drivers/block/xen-blkfront.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 5265975b3fba..5a93f7cc2939 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
 
 static void blkfront_setup_discard(struct blkfront_info *info)
 {
-	int err;
-	unsigned int discard_granularity;
-	unsigned int discard_alignment;
+	unsigned int discard_granularity = 0;
+	unsigned int discard_alignment = 0;
+	unsigned int discard_secure = 0;
 
-	info->feature_discard = 1;
-	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+	xenbus_gather(XBT_NIL, info->xbdev->otherend,
 		"discard-granularity", "%u", &discard_granularity,
 		"discard-alignment", "%u", &discard_alignment,
+		"discard-secure", "%u", &discard_secure,
 		NULL);
-	if (!err) {
-		info->discard_granularity = discard_granularity;
-		info->discard_alignment = discard_alignment;
-	}
-	info->feature_secdiscard =
-		!!xenbus_read_unsigned(info->xbdev->otherend, "discard-secure",
-				       0);
+
+	if (!discard_granularity)
+		return;
+
+	info->feature_discard = 1;
+	info->discard_granularity = discard_granularity;
+	info->discard_alignment = discard_alignment;
+	info->feature_secdiscard = !!discard_secure;
 }
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo)
-- 
2.29.2

Re: [PATCH] xen-blkfront: don't make discard-alignment mandatory

[Jürgen Groß]

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On 18.01.21 16:15, Roger Pau Monne wrote:
> Don't require the discard-alignment xenstore node to be present in
> order to correctly setup the feature. This can happen with versions of
> QEMU that only write the discard-granularity but not the
> discard-alignment node.
> 
> Assume discard-alignment is 0 if not present. While there also fix the
> logic to not enable the discard feature if discard-granularity is not
> present.
> 
> Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: "Roger Pau Monné" <roger.pau@citrix.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: xen-devel@lists.xenproject.org
> Cc: linux-block@vger.kernel.org
> Cc: Arthur Borsboom <arthurborsboom@gmail.com>
> ---
>   drivers/block/xen-blkfront.c | 25 +++++++++++++------------
>   1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 5265975b3fba..5a93f7cc2939 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
>   
>   static void blkfront_setup_discard(struct blkfront_info *info)
>   {
> -	int err;
> -	unsigned int discard_granularity;
> -	unsigned int discard_alignment;
> +	unsigned int discard_granularity = 0;
> +	unsigned int discard_alignment = 0;
> +	unsigned int discard_secure = 0;
>   
> -	info->feature_discard = 1;
> -	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> +	xenbus_gather(XBT_NIL, info->xbdev->otherend,
>   		"discard-granularity", "%u", &discard_granularity,
>   		"discard-alignment", "%u", &discard_alignment,
> +		"discard-secure", "%u", &discard_secure,
>   		NULL);

This would mean that "discard-secure" will be evaluated only if the
other two items are set in Xenstore. From blkif.h I can't see this is
required, and your patch is modifying today's behavior in this regard.

You might want to have three xenbus_read_unsigned() calls instead.


Juergen

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Re: [PATCH] xen-blkfront: don't make discard-alignment mandatory

[Roger Pau Monné]

On Tue, Jan 19, 2021 at 08:43:01AM +0100, Jürgen Groß wrote:
> On 18.01.21 16:15, Roger Pau Monne wrote:
> > Don't require the discard-alignment xenstore node to be present in
> > order to correctly setup the feature. This can happen with versions of
> > QEMU that only write the discard-granularity but not the
> > discard-alignment node.
> > 
> > Assume discard-alignment is 0 if not present. While there also fix the
> > logic to not enable the discard feature if discard-granularity is not
> > present.
> > 
> > Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > Cc: Juergen Gross <jgross@suse.com>
> > Cc: Stefano Stabellini <sstabellini@kernel.org>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > Cc: "Roger Pau Monné" <roger.pau@citrix.com>
> > Cc: Jens Axboe <axboe@kernel.dk>
> > Cc: xen-devel@lists.xenproject.org
> > Cc: linux-block@vger.kernel.org
> > Cc: Arthur Borsboom <arthurborsboom@gmail.com>
> > ---
> >   drivers/block/xen-blkfront.c | 25 +++++++++++++------------
> >   1 file changed, 13 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > index 5265975b3fba..5a93f7cc2939 100644
> > --- a/drivers/block/xen-blkfront.c
> > +++ b/drivers/block/xen-blkfront.c
> > @@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
> >   static void blkfront_setup_discard(struct blkfront_info *info)
> >   {
> > -	int err;
> > -	unsigned int discard_granularity;
> > -	unsigned int discard_alignment;
> > +	unsigned int discard_granularity = 0;
> > +	unsigned int discard_alignment = 0;
> > +	unsigned int discard_secure = 0;
> > -	info->feature_discard = 1;
> > -	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> > +	xenbus_gather(XBT_NIL, info->xbdev->otherend,
> >   		"discard-granularity", "%u", &discard_granularity,
> >   		"discard-alignment", "%u", &discard_alignment,
> > +		"discard-secure", "%u", &discard_secure,
> >   		NULL);
> 
> This would mean that "discard-secure" will be evaluated only if the
> other two items are set in Xenstore. From blkif.h I can't see this is
> required, and your patch is modifying today's behavior in this regard.
> 
> You might want to have three xenbus_read_unsigned() calls instead.

You are right, discard-secure should be fetched regardless of whether
discard-alignment exists.

I can fetch discard-granularity and discard-alignment using
xenbus_gather and keep discard-secure using xenbus_read_unsigned. Let
me send a new version.

Thanks, Roger.

Re: [PATCH] xen-blkfront: don't make discard-alignment mandatory

[Jürgen Groß]

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On 19.01.21 11:06, Roger Pau Monné wrote:
> On Tue, Jan 19, 2021 at 08:43:01AM +0100, Jürgen Groß wrote:
>> On 18.01.21 16:15, Roger Pau Monne wrote:
>>> Don't require the discard-alignment xenstore node to be present in
>>> order to correctly setup the feature. This can happen with versions of
>>> QEMU that only write the discard-granularity but not the
>>> discard-alignment node.
>>>
>>> Assume discard-alignment is 0 if not present. While there also fix the
>>> logic to not enable the discard feature if discard-granularity is not
>>> present.
>>>
>>> Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>>> ---
>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>> Cc: Juergen Gross <jgross@suse.com>
>>> Cc: Stefano Stabellini <sstabellini@kernel.org>
>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>> Cc: "Roger Pau Monné" <roger.pau@citrix.com>
>>> Cc: Jens Axboe <axboe@kernel.dk>
>>> Cc: xen-devel@lists.xenproject.org
>>> Cc: linux-block@vger.kernel.org
>>> Cc: Arthur Borsboom <arthurborsboom@gmail.com>
>>> ---
>>>    drivers/block/xen-blkfront.c | 25 +++++++++++++------------
>>>    1 file changed, 13 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>>> index 5265975b3fba..5a93f7cc2939 100644
>>> --- a/drivers/block/xen-blkfront.c
>>> +++ b/drivers/block/xen-blkfront.c
>>> @@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
>>>    static void blkfront_setup_discard(struct blkfront_info *info)
>>>    {
>>> -	int err;
>>> -	unsigned int discard_granularity;
>>> -	unsigned int discard_alignment;
>>> +	unsigned int discard_granularity = 0;
>>> +	unsigned int discard_alignment = 0;
>>> +	unsigned int discard_secure = 0;
>>> -	info->feature_discard = 1;
>>> -	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
>>> +	xenbus_gather(XBT_NIL, info->xbdev->otherend,
>>>    		"discard-granularity", "%u", &discard_granularity,
>>>    		"discard-alignment", "%u", &discard_alignment,
>>> +		"discard-secure", "%u", &discard_secure,
>>>    		NULL);
>>
>> This would mean that "discard-secure" will be evaluated only if the
>> other two items are set in Xenstore. From blkif.h I can't see this is
>> required, and your patch is modifying today's behavior in this regard.
>>
>> You might want to have three xenbus_read_unsigned() calls instead.
> 
> You are right, discard-secure should be fetched regardless of whether
> discard-alignment exists.
> 
> I can fetch discard-granularity and discard-alignment using
> xenbus_gather and keep discard-secure using xenbus_read_unsigned. Let
> me send a new version.

I'm still not convinced this is correct. blkif.h doesn't mention that
discard-alignment will be valid only with discard-granularity being
present.


Juergen

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Re: [PATCH] xen-blkfront: don't make discard-alignment mandatory

[Roger Pau Monné]

On Tue, Jan 19, 2021 at 11:11:26AM +0100, Jürgen Groß wrote:
> On 19.01.21 11:06, Roger Pau Monné wrote:
> > On Tue, Jan 19, 2021 at 08:43:01AM +0100, Jürgen Groß wrote:
> > > On 18.01.21 16:15, Roger Pau Monne wrote:
> > > > Don't require the discard-alignment xenstore node to be present in
> > > > order to correctly setup the feature. This can happen with versions of
> > > > QEMU that only write the discard-granularity but not the
> > > > discard-alignment node.
> > > > 
> > > > Assume discard-alignment is 0 if not present. While there also fix the
> > > > logic to not enable the discard feature if discard-granularity is not
> > > > present.
> > > > 
> > > > Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
> > > > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > > > ---
> > > > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > > > Cc: Juergen Gross <jgross@suse.com>
> > > > Cc: Stefano Stabellini <sstabellini@kernel.org>
> > > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > > > Cc: "Roger Pau Monné" <roger.pau@citrix.com>
> > > > Cc: Jens Axboe <axboe@kernel.dk>
> > > > Cc: xen-devel@lists.xenproject.org
> > > > Cc: linux-block@vger.kernel.org
> > > > Cc: Arthur Borsboom <arthurborsboom@gmail.com>
> > > > ---
> > > >    drivers/block/xen-blkfront.c | 25 +++++++++++++------------
> > > >    1 file changed, 13 insertions(+), 12 deletions(-)
> > > > 
> > > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > > > index 5265975b3fba..5a93f7cc2939 100644
> > > > --- a/drivers/block/xen-blkfront.c
> > > > +++ b/drivers/block/xen-blkfront.c
> > > > @@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
> > > >    static void blkfront_setup_discard(struct blkfront_info *info)
> > > >    {
> > > > -	int err;
> > > > -	unsigned int discard_granularity;
> > > > -	unsigned int discard_alignment;
> > > > +	unsigned int discard_granularity = 0;
> > > > +	unsigned int discard_alignment = 0;
> > > > +	unsigned int discard_secure = 0;
> > > > -	info->feature_discard = 1;
> > > > -	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> > > > +	xenbus_gather(XBT_NIL, info->xbdev->otherend,
> > > >    		"discard-granularity", "%u", &discard_granularity,
> > > >    		"discard-alignment", "%u", &discard_alignment,
> > > > +		"discard-secure", "%u", &discard_secure,
> > > >    		NULL);
> > > 
> > > This would mean that "discard-secure" will be evaluated only if the
> > > other two items are set in Xenstore. From blkif.h I can't see this is
> > > required, and your patch is modifying today's behavior in this regard.
> > > 
> > > You might want to have three xenbus_read_unsigned() calls instead.
> > 
> > You are right, discard-secure should be fetched regardless of whether
> > discard-alignment exists.
> > 
> > I can fetch discard-granularity and discard-alignment using
> > xenbus_gather and keep discard-secure using xenbus_read_unsigned. Let
> > me send a new version.
> 
> I'm still not convinced this is correct. blkif.h doesn't mention that
> discard-alignment will be valid only with discard-granularity being
> present.

No, in fact I think I need to rework this a little further. Just
having feature-discard = 1 should enable the discard functionality, by
setting discard-granularity = physical block size and
discard-alignment = 0.

Roger.