RE: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> -Original Message-
> From: Alex Williamson
> Sent: Tuesday, August 27, 2019 9:55 PM
> To: Parav Pandit
> Cc: Cornelia Huck ; Jiri Pirko ;
> kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org;
> linux-kernel@vger.kernel.org; net...@vger.kernel.org
> Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
>
> On Tue, 27 Aug 2019 16:13:27 +
> Parav Pandit wrote:
>
> > > -Original Message-
> > > From: Alex Williamson
> > > Sent: Tuesday, August 27, 2019 8:59 PM
> > > To: Cornelia Huck
> > > Cc: Parav Pandit ; Jiri Pirko
> > > ; kwankh...@nvidia.com; da...@davemloft.net;
> > > k...@vger.kernel.org; linux- ker...@vger.kernel.org;
> > > net...@vger.kernel.org
> > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all
> > > mdevs
> > >
> > > On Tue, 27 Aug 2019 13:29:46 +0200
> > > Cornelia Huck wrote:
> > >
> > > > On Tue, 27 Aug 2019 11:08:59 + Parav Pandit
> > > > wrote:
> > > >
> > > > > > -Original Message-
> > > > > > From: Cornelia Huck
> > > > > > Sent: Tuesday, August 27, 2019 3:59 PM
> > > > > > To: Parav Pandit
> > > > > > Cc: alex.william...@redhat.com; Jiri Pirko
> > > > > > ; kwankh...@nvidia.com;
> > > > > > da...@davemloft.net; k...@vger.kernel.org;
> > > > > > linux- ker...@vger.kernel.org; net...@vger.kernel.org
> > > > > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among
> > > > > > all mdevs
> > > > > >
> > > > > > On Mon, 26 Aug 2019 15:41:17 -0500 Parav Pandit
> > > > > > wrote:
> > > > > >
> > > > > > > Mdev alias should be unique among all the mdevs, so that
> > > > > > > when such alias is used by the mdev users to derive other
> > > > > > > objects, there is no collision in a given system.
> > > > > > >
> > > > > > > Signed-off-by: Parav Pandit
> > > > > > > ---
> > > > > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > > > > 1 file changed, 5 insertions(+)
> > > > > > >
> > > > > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > > > > b/drivers/vfio/mdev/mdev_core.c index
> > > > > > > e825ff38b037..6eb37f0c6369
> > > > > > > 100644
> > > > > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject
> > > > > > > *kobj,
> > > struct
> > > > > > device *dev,
> > > > > > > ret = -EEXIST;
> > > > > > > goto mdev_fail;
> > > > > > > }
> > > > > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > > > > >
> > > > > > Any way we can relay to the caller that the uuid was fine, but
> > > > > > that we had a hash collision? Duplicate uuids are much more
> > > > > > obvious than
> > > a collision here.
> > > > > >
> > > > > How do you want to relay this rare event?
> > > > > Netlink interface has way to return the error message back, but
> > > > > sysfs is
> > > limited due to its error code based interface.
> > > >
> > > > I don't know, that's why I asked :)
> > > >
> > > > The problem is that "uuid already used" and "hash collision" are
> > > > indistinguishable. While "use a different uuid" will probably work
> > > > in both cases, "increase alias length" might be a good alternative
> > > > in some cases.
> > > >
> > > > But if there is no good way to relay the problem, we can live with it.
> > >
> > > It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias
> \"%s\"
> > > for mdev device %pUl\n",...
> > >
> > Ok.
> > dev_dbg_once() to avoid message flood.
>
> I'd suggest a rate-limit rather than a once. The fact that the kernel may
> have
> experienced a collision at some time in the past does not help someone
> debug why they can't create a device now. The only way we're going to get a
> flood is if a user sufficiently privileged to create mdev devices stumbles
> onto
> a collision and continues to repeat the same operation. That falls into
> shoot-yourself-in-the-foot behavior imo.
> Thanks,
>
Ok. Will do.
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Tue, 27 Aug 2019 16:13:27 +
Parav Pandit wrote:
> > -Original Message-
> > From: Alex Williamson
> > Sent: Tuesday, August 27, 2019 8:59 PM
> > To: Cornelia Huck
> > Cc: Parav Pandit ; Jiri Pirko ;
> > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> > ker...@vger.kernel.org; net...@vger.kernel.org
> > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> >
> > On Tue, 27 Aug 2019 13:29:46 +0200
> > Cornelia Huck wrote:
> >
> > > On Tue, 27 Aug 2019 11:08:59 +
> > > Parav Pandit wrote:
> > >
> > > > > -Original Message-
> > > > > From: Cornelia Huck
> > > > > Sent: Tuesday, August 27, 2019 3:59 PM
> > > > > To: Parav Pandit
> > > > > Cc: alex.william...@redhat.com; Jiri Pirko ;
> > > > > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org;
> > > > > linux- ker...@vger.kernel.org; net...@vger.kernel.org
> > > > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all
> > > > > mdevs
> > > > >
> > > > > On Mon, 26 Aug 2019 15:41:17 -0500 Parav Pandit
> > > > > wrote:
> > > > >
> > > > > > Mdev alias should be unique among all the mdevs, so that when
> > > > > > such alias is used by the mdev users to derive other objects,
> > > > > > there is no collision in a given system.
> > > > > >
> > > > > > Signed-off-by: Parav Pandit
> > > > > > ---
> > > > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > > > 1 file changed, 5 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > > > > 100644
> > > > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> > struct
> > > > > device *dev,
> > > > > > ret = -EEXIST;
> > > > > > goto mdev_fail;
> > > > > > }
> > > > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > > > >
> > > > > Any way we can relay to the caller that the uuid was fine, but
> > > > > that we had a hash collision? Duplicate uuids are much more obvious
> > > > > than
> > a collision here.
> > > > >
> > > > How do you want to relay this rare event?
> > > > Netlink interface has way to return the error message back, but sysfs
> > > > is
> > limited due to its error code based interface.
> > >
> > > I don't know, that's why I asked :)
> > >
> > > The problem is that "uuid already used" and "hash collision" are
> > > indistinguishable. While "use a different uuid" will probably work in
> > > both cases, "increase alias length" might be a good alternative in
> > > some cases.
> > >
> > > But if there is no good way to relay the problem, we can live with it.
> >
> > It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias
> > \"%s\"
> > for mdev device %pUl\n",...
> >
> Ok.
> dev_dbg_once() to avoid message flood.
I'd suggest a rate-limit rather than a once. The fact that the kernel
may have experienced a collision at some time in the past does not help
someone debug why they can't create a device now. The only way we're
going to get a flood is if a user sufficiently privileged to create
mdev devices stumbles onto a collision and continues to repeat the same
operation. That falls into shoot-yourself-in-the-foot behavior imo.
Thanks,
Alex
RE: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> -Original Message-
> From: Alex Williamson
> Sent: Tuesday, August 27, 2019 8:54 PM
> To: Parav Pandit
> Cc: Mark Bloch ; Jiri Pirko ;
> kwankh...@nvidia.com; coh...@redhat.com; da...@davemloft.net;
> k...@vger.kernel.org; linux-kernel@vger.kernel.org; net...@vger.kernel.org
> Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
>
> On Tue, 27 Aug 2019 04:28:37 +
> Parav Pandit wrote:
>
> > Hi Mark,
> >
> > > -Original Message-
> > > From: Mark Bloch
> > > Sent: Tuesday, August 27, 2019 4:32 AM
> > > To: Parav Pandit ; alex.william...@redhat.com;
> > > Jiri Pirko ; kwankh...@nvidia.com;
> > > coh...@redhat.com; da...@davemloft.net
> > > Cc: k...@vger.kernel.org; linux-kernel@vger.kernel.org;
> > > net...@vger.kernel.org
> > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all
> > > mdevs
> > >
> > >
> > >
> > > On 8/26/19 1:41 PM, Parav Pandit wrote:
> > > > Mdev alias should be unique among all the mdevs, so that when such
> > > > alias is used by the mdev users to derive other objects, there is
> > > > no collision in a given system.
> > > >
> > > > Signed-off-by: Parav Pandit
> > > > ---
> > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > 1 file changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > > 100644
> > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> > > struct device *dev,
> > > > ret = -EEXIST;
> > > > goto mdev_fail;
> > > > }
> > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > >
> > > alias can be NULL here no?
> > >
> > If alias is NULL, tmp->alias would also be null because for given parent
> > either
> we have alias or we don’t.
> > So its not possible to have tmp->alias as null and alias as non null.
> > But it may be good/defensive to add check for both.
>
> mdev_list is a global list of all mdev devices, how can we make any
> assumptions that an element has the same parent? Thanks,
>
Oh yes, right. If tmp->alias is not_null but alias can be NULL.
I will fix the check.
> Alex
>
> > > > + mutex_unlock(_list_lock);
> > > > + ret = -EEXIST;
> > > > + goto mdev_fail;
> > > > + }
> > > > }
> > > >
> > > > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> > > >
> > >
> > > Mark
RE: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> -Original Message-
> From: Alex Williamson
> Sent: Tuesday, August 27, 2019 8:59 PM
> To: Cornelia Huck
> Cc: Parav Pandit ; Jiri Pirko ;
> kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> ker...@vger.kernel.org; net...@vger.kernel.org
> Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
>
> On Tue, 27 Aug 2019 13:29:46 +0200
> Cornelia Huck wrote:
>
> > On Tue, 27 Aug 2019 11:08:59 +
> > Parav Pandit wrote:
> >
> > > > -Original Message-
> > > > From: Cornelia Huck
> > > > Sent: Tuesday, August 27, 2019 3:59 PM
> > > > To: Parav Pandit
> > > > Cc: alex.william...@redhat.com; Jiri Pirko ;
> > > > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org;
> > > > linux- ker...@vger.kernel.org; net...@vger.kernel.org
> > > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all
> > > > mdevs
> > > >
> > > > On Mon, 26 Aug 2019 15:41:17 -0500 Parav Pandit
> > > > wrote:
> > > >
> > > > > Mdev alias should be unique among all the mdevs, so that when
> > > > > such alias is used by the mdev users to derive other objects,
> > > > > there is no collision in a given system.
> > > > >
> > > > > Signed-off-by: Parav Pandit
> > > > > ---
> > > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > > 1 file changed, 5 insertions(+)
> > > > >
> > > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > > > 100644
> > > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> struct
> > > > device *dev,
> > > > > ret = -EEXIST;
> > > > > goto mdev_fail;
> > > > > }
> > > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > > >
> > > > Any way we can relay to the caller that the uuid was fine, but
> > > > that we had a hash collision? Duplicate uuids are much more obvious than
> a collision here.
> > > >
> > > How do you want to relay this rare event?
> > > Netlink interface has way to return the error message back, but sysfs is
> limited due to its error code based interface.
> >
> > I don't know, that's why I asked :)
> >
> > The problem is that "uuid already used" and "hash collision" are
> > indistinguishable. While "use a different uuid" will probably work in
> > both cases, "increase alias length" might be a good alternative in
> > some cases.
> >
> > But if there is no good way to relay the problem, we can live with it.
>
> It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias
> \"%s\"
> for mdev device %pUl\n",...
>
Ok.
dev_dbg_once() to avoid message flood.
> Thanks,
> Alex
>
> > > > > + mutex_unlock(_list_lock);
> > > > > + ret = -EEXIST;
> > > > > + goto mdev_fail;
> > > > > + }
> > > > > }
> > > > >
> > > > > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> > >
> >
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Tue, 27 Aug 2019 09:28:55 -0600
Alex Williamson wrote:
> On Tue, 27 Aug 2019 13:29:46 +0200
> Cornelia Huck wrote:
>
> > On Tue, 27 Aug 2019 11:08:59 +
> > Parav Pandit wrote:
> >
> > > > -Original Message-
> > > > From: Cornelia Huck
> > > > Sent: Tuesday, August 27, 2019 3:59 PM
> > > > To: Parav Pandit
> > > > Cc: alex.william...@redhat.com; Jiri Pirko ;
> > > > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> > > > ker...@vger.kernel.org; net...@vger.kernel.org
> > > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> > > >
> > > > On Mon, 26 Aug 2019 15:41:17 -0500
> > > > Parav Pandit wrote:
> > > >
> > > > > Mdev alias should be unique among all the mdevs, so that when such
> > > > > alias is used by the mdev users to derive other objects, there is no
> > > > > collision in a given system.
> > > > >
> > > > > Signed-off-by: Parav Pandit
> > > > > ---
> > > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > > 1 file changed, 5 insertions(+)
> > > > >
> > > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > > > 100644
> > > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> > > > > struct
> > > > device *dev,
> > > > > ret = -EEXIST;
> > > > > goto mdev_fail;
> > > > > }
> > > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > > > >
> > > >
> > > > Any way we can relay to the caller that the uuid was fine, but that we
> > > > had a
> > > > hash collision? Duplicate uuids are much more obvious than a collision
> > > > here.
> > > >
> > > How do you want to relay this rare event?
> > > Netlink interface has way to return the error message back, but sysfs is
> > > limited due to its error code based interface.
> >
> > I don't know, that's why I asked :)
> >
> > The problem is that "uuid already used" and "hash collision" are
> > indistinguishable. While "use a different uuid" will probably work in
> > both cases, "increase alias length" might be a good alternative in some
> > cases.
> >
> > But if there is no good way to relay the problem, we can live with it.
>
> It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias
> \"%s\" for mdev device %pUl\n",...
Sounds good to me.
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Tue, 27 Aug 2019 13:29:46 +0200
Cornelia Huck wrote:
> On Tue, 27 Aug 2019 11:08:59 +
> Parav Pandit wrote:
>
> > > -Original Message-
> > > From: Cornelia Huck
> > > Sent: Tuesday, August 27, 2019 3:59 PM
> > > To: Parav Pandit
> > > Cc: alex.william...@redhat.com; Jiri Pirko ;
> > > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> > > ker...@vger.kernel.org; net...@vger.kernel.org
> > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> > >
> > > On Mon, 26 Aug 2019 15:41:17 -0500
> > > Parav Pandit wrote:
> > >
> > > > Mdev alias should be unique among all the mdevs, so that when such
> > > > alias is used by the mdev users to derive other objects, there is no
> > > > collision in a given system.
> > > >
> > > > Signed-off-by: Parav Pandit
> > > > ---
> > > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > > 1 file changed, 5 insertions(+)
> > > >
> > > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > > 100644
> > > > --- a/drivers/vfio/mdev/mdev_core.c
> > > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> > > > struct
> > > device *dev,
> > > > ret = -EEXIST;
> > > > goto mdev_fail;
> > > > }
> > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> > >
> > > Any way we can relay to the caller that the uuid was fine, but that we
> > > had a
> > > hash collision? Duplicate uuids are much more obvious than a collision
> > > here.
> > >
> > How do you want to relay this rare event?
> > Netlink interface has way to return the error message back, but sysfs is
> > limited due to its error code based interface.
>
> I don't know, that's why I asked :)
>
> The problem is that "uuid already used" and "hash collision" are
> indistinguishable. While "use a different uuid" will probably work in
> both cases, "increase alias length" might be a good alternative in some
> cases.
>
> But if there is no good way to relay the problem, we can live with it.
It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias
\"%s\" for mdev device %pUl\n",...
Thanks,
Alex
> > > > + mutex_unlock(_list_lock);
> > > > + ret = -EEXIST;
> > > > + goto mdev_fail;
> > > > + }
> > > > }
> > > >
> > > > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> >
>
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Tue, 27 Aug 2019 04:28:37 +
Parav Pandit wrote:
> Hi Mark,
>
> > -Original Message-
> > From: Mark Bloch
> > Sent: Tuesday, August 27, 2019 4:32 AM
> > To: Parav Pandit ; alex.william...@redhat.com; Jiri
> > Pirko ; kwankh...@nvidia.com; coh...@redhat.com;
> > da...@davemloft.net
> > Cc: k...@vger.kernel.org; linux-kernel@vger.kernel.org;
> > net...@vger.kernel.org
> > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> >
> >
> >
> > On 8/26/19 1:41 PM, Parav Pandit wrote:
> > > Mdev alias should be unique among all the mdevs, so that when such
> > > alias is used by the mdev users to derive other objects, there is no
> > > collision in a given system.
> > >
> > > Signed-off-by: Parav Pandit
> > > ---
> > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > 1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > 100644
> > > --- a/drivers/vfio/mdev/mdev_core.c
> > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> > struct device *dev,
> > > ret = -EEXIST;
> > > goto mdev_fail;
> > > }
> > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> >
> > alias can be NULL here no?
> >
> If alias is NULL, tmp->alias would also be null because for given parent
> either we have alias or we don’t.
> So its not possible to have tmp->alias as null and alias as non null.
> But it may be good/defensive to add check for both.
mdev_list is a global list of all mdev devices, how can we make any
assumptions that an element has the same parent? Thanks,
Alex
> > > + mutex_unlock(_list_lock);
> > > + ret = -EEXIST;
> > > + goto mdev_fail;
> > > + }
> > > }
> > >
> > > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> > >
> >
> > Mark
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Tue, 27 Aug 2019 11:08:59 +
Parav Pandit wrote:
> > -Original Message-
> > From: Cornelia Huck
> > Sent: Tuesday, August 27, 2019 3:59 PM
> > To: Parav Pandit
> > Cc: alex.william...@redhat.com; Jiri Pirko ;
> > kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> > ker...@vger.kernel.org; net...@vger.kernel.org
> > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> >
> > On Mon, 26 Aug 2019 15:41:17 -0500
> > Parav Pandit wrote:
> >
> > > Mdev alias should be unique among all the mdevs, so that when such
> > > alias is used by the mdev users to derive other objects, there is no
> > > collision in a given system.
> > >
> > > Signed-off-by: Parav Pandit
> > > ---
> > > drivers/vfio/mdev/mdev_core.c | 5 +
> > > 1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/vfio/mdev/mdev_core.c
> > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > > 100644
> > > --- a/drivers/vfio/mdev/mdev_core.c
> > > +++ b/drivers/vfio/mdev/mdev_core.c
> > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj, struct
> > device *dev,
> > > ret = -EEXIST;
> > > goto mdev_fail;
> > > }
> > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
> >
> > Any way we can relay to the caller that the uuid was fine, but that we had a
> > hash collision? Duplicate uuids are much more obvious than a collision here.
> >
> How do you want to relay this rare event?
> Netlink interface has way to return the error message back, but sysfs is
> limited due to its error code based interface.
I don't know, that's why I asked :)
The problem is that "uuid already used" and "hash collision" are
indistinguishable. While "use a different uuid" will probably work in
both cases, "increase alias length" might be a good alternative in some
cases.
But if there is no good way to relay the problem, we can live with it.
>
> > > + mutex_unlock(_list_lock);
> > > + ret = -EEXIST;
> > > + goto mdev_fail;
> > > + }
> > > }
> > >
> > > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
>
RE: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
> -Original Message-
> From: Cornelia Huck
> Sent: Tuesday, August 27, 2019 3:59 PM
> To: Parav Pandit
> Cc: alex.william...@redhat.com; Jiri Pirko ;
> kwankh...@nvidia.com; da...@davemloft.net; k...@vger.kernel.org; linux-
> ker...@vger.kernel.org; net...@vger.kernel.org
> Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
>
> On Mon, 26 Aug 2019 15:41:17 -0500
> Parav Pandit wrote:
>
> > Mdev alias should be unique among all the mdevs, so that when such
> > alias is used by the mdev users to derive other objects, there is no
> > collision in a given system.
> >
> > Signed-off-by: Parav Pandit
> > ---
> > drivers/vfio/mdev/mdev_core.c | 5 +
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/vfio/mdev/mdev_core.c
> > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj, struct
> device *dev,
> > ret = -EEXIST;
> > goto mdev_fail;
> > }
> > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
>
> Any way we can relay to the caller that the uuid was fine, but that we had a
> hash collision? Duplicate uuids are much more obvious than a collision here.
>
How do you want to relay this rare event?
Netlink interface has way to return the error message back, but sysfs is
limited due to its error code based interface.
> > + mutex_unlock(_list_lock);
> > + ret = -EEXIST;
> > + goto mdev_fail;
> > + }
> > }
> >
> > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On Mon, 26 Aug 2019 15:41:17 -0500
Parav Pandit wrote:
> Mdev alias should be unique among all the mdevs, so that when such alias
> is used by the mdev users to derive other objects, there is no
> collision in a given system.
>
> Signed-off-by: Parav Pandit
> ---
> drivers/vfio/mdev/mdev_core.c | 5 +
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index e825ff38b037..6eb37f0c6369 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj, struct
> device *dev,
> ret = -EEXIST;
> goto mdev_fail;
> }
> + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
Any way we can relay to the caller that the uuid was fine, but that we
had a hash collision? Duplicate uuids are much more obvious than a
collision here.
> + mutex_unlock(_list_lock);
> + ret = -EEXIST;
> + goto mdev_fail;
> + }
> }
>
> mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
RE: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
Hi Mark,
> -Original Message-
> From: Mark Bloch
> Sent: Tuesday, August 27, 2019 4:32 AM
> To: Parav Pandit ; alex.william...@redhat.com; Jiri
> Pirko ; kwankh...@nvidia.com; coh...@redhat.com;
> da...@davemloft.net
> Cc: k...@vger.kernel.org; linux-kernel@vger.kernel.org;
> net...@vger.kernel.org
> Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
>
>
>
> On 8/26/19 1:41 PM, Parav Pandit wrote:
> > Mdev alias should be unique among all the mdevs, so that when such
> > alias is used by the mdev users to derive other objects, there is no
> > collision in a given system.
> >
> > Signed-off-by: Parav Pandit
> > ---
> > drivers/vfio/mdev/mdev_core.c | 5 +
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/vfio/mdev/mdev_core.c
> > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369
> > 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj,
> struct device *dev,
> > ret = -EEXIST;
> > goto mdev_fail;
> > }
> > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
>
> alias can be NULL here no?
>
If alias is NULL, tmp->alias would also be null because for given parent either
we have alias or we don’t.
So its not possible to have tmp->alias as null and alias as non null.
But it may be good/defensive to add check for both.
> > + mutex_unlock(_list_lock);
> > + ret = -EEXIST;
> > + goto mdev_fail;
> > + }
> > }
> >
> > mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
> >
>
> Mark
Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs
On 8/26/19 1:41 PM, Parav Pandit wrote:
> Mdev alias should be unique among all the mdevs, so that when such alias
> is used by the mdev users to derive other objects, there is no
> collision in a given system.
>
> Signed-off-by: Parav Pandit
> ---
> drivers/vfio/mdev/mdev_core.c | 5 +
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index e825ff38b037..6eb37f0c6369 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj, struct
> device *dev,
> ret = -EEXIST;
> goto mdev_fail;
> }
> + if (tmp->alias && strcmp(tmp->alias, alias) == 0) {
alias can be NULL here no?
> + mutex_unlock(_list_lock);
> + ret = -EEXIST;
> + goto mdev_fail;
> + }
> }
>
> mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
>
Mark
