On Thu, May 09, 2019 at 11:24:49PM +0800, Cornelia Huck wrote: > On Wed, 8 May 2019 07:57:05 -0400 > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > On Tue, May 07, 2019 at 05:19:54PM +0800, Cornelia Huck wrote: > > > On Sun, 5 May 2019 21:49:04 -0400 > > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > > > version attribute is used to check two mdev devices' compatibility. > > > > > > > > The key point of this version attribute is that it's rw. > > > > User space has no need to understand internal of device version and no > > > > need to compare versions by itself. > > > > Compared to reading version strings from both two mdev devices being > > > > checked, user space only reads from one mdev device's version attribute. > > > > After getting its version string, user space writes this string into the > > > > other mdev device's version attribute. Vendor driver of mdev device > > > > whose version attribute being written will check device compatibility of > > > > the two mdev devices for user space and return success for compatibility > > > > or errno for incompatibility. > > > > > > I'm still missing a bit _what_ is actually supposed to be > > > compatible/incompatible. I'd assume some internal state descriptions > > > (even if this is not actually limited to migration). > > > > > right. > > originally, I thought this attribute should only contain a device's hardware > > compatibility info. But seems also including vendor specific software migration > > version is more reasonable, because general VFIO migration code cannot know > > version of vendor specific software migration code until migration data is > > transferring to the target vm. Then renaming it to migration_version is more > > appropriate. > > :) > > Nod. > > (...) > > > > > @@ -246,6 +249,143 @@ Directories and files under the sysfs for Each Physical Device > > > > This attribute should show the number of devices of type <type-id> that can be > > > > created. > > > > > > > > +* version > > > > + > > > > + This attribute is rw, and is optional. > > > > + It is used to check device compatibility between two mdev devices and is > > > > + accessed in pairs between the two mdev devices being checked. > > > > + The intent of this attribute is to make an mdev device's version opaque to > > > > + user space, so instead of reading two mdev devices' version strings and > > > > + comparing in userspace, user space should only read one mdev device's version > > > > + attribute, and writes this version string into the other mdev device's version > > > > + attribute. Then vendor driver of mdev device whose version attribute being > > > > + written would check the incoming version string and tell user space whether > > > > + the two mdev devices are compatible via return value. That's why this > > > > + attribute is writable. > > > > > > I would reword this a bit: > > > > > > "This attribute provides a way to check device compatibility between > > > two mdev devices from userspace. The intended usage is for userspace to > > > read the version attribute from one mdev device and then writing that > > > value to the version attribute of the other mdev device. The second > > > mdev device indicates compatibility via the return code of the write > > > operation. This makes compatibility between mdev devices completely > > > vendor-defined and opaque to userspace." > > > > > > We still should explain _what_ compatibility we're talking about here, > > > though. > > > > > Thanks. It's much better than mine:) > > Then I'll change compatibility --> migration compatibility. > > Ok, with that it should be clear enough. > > > > > > > + > > > > + when reading this attribute, it should show device version string of > > > > + the device of type <type-id>. > > > > + > > > > + This string is private to vendor driver itself. Vendor driver is able to > > > > + freely define format and length of device version string. > > > > + e.g. It can use a combination of pciid of parent device + mdev type. > > > > + > > > > + When writing a string to this attribute, vendor driver should analyze this > > > > + string and check whether the mdev device being identified by this string is > > > > + compatible with the mdev device for this attribute. vendor driver should then > > > > + return written string's length if it regards the two mdev devices are > > > > + compatible; vendor driver should return negative errno if it regards the two > > > > + mdev devices are not compatible. > > > > + > > > > + User space should treat ANY of below conditions as two mdev devices not > > > > + compatible: > > > > + (1) any one of the two mdev devices does not have a version attribute > > > > + (2) error when read from one mdev device's version attribute > > > > > > s/read/reading/ > > > > > > > + (3) error when write one mdev device's version string to the other mdev > > > > > > s/write/writing/ > > > > > > > + device's version attribute > > > > + > > > > + User space should regard two mdev devices compatible when ALL of below > > > > + conditions are met: > > > > + (1) success when read from one mdev device's version attribute. > > > > > > s/read/reading/ > > > > > > > + (2) success when write one mdev device's version string to the other mdev > > > > > > s/write/writing/ > > got it. thanks for pointing them out:) > > > > > > > + device's version attribute > > > > + > > > > + Errno: > > > > + If vendor driver wants to claim a mdev device incompatible to all other mdev > > > > > > "If the vendor driver wants to designate a mdev device..." > > > > > ok. thanks:) > > > > + devices, it should not register version attribute for this mdev device. But if > > > > + a vendor driver has already registered version attribute and it wants to claim > > > > + a mdev device incompatible to all other mdev devices, it needs to return > > > > + -ENODEV on access to this mdev device's version attribute. > > > > + If a mdev device is only incompatible to certain mdev devices, write of > > > > + incompatible mdev devices's version strings to its version attribute should > > > > + return -EINVAL; > > > > > > > > > Maybe put the defined return code into a bulleted list instead? But > > > this looks reasonable as well. > > > > > as user space have no idea of those errno and only gets 0/1 as return code from > > read/write. maybe I can move this description of errno to patch 2/2 as an > > example? > > Confused. They should get -EINVAL/-ENODEV/... all right, shouldn't they? > sorry. my previous statement is not right. read(2)/write(2) return -1 on error, error cause is returned through errno. So, it's also fine if we can get an agreement in this doc that -ENODEV meaning a mdev device is not compatible to all devices, -EINVAL meaning a mdev device is not compatible to specified device. > > > > > > + > > > > + This attribute can be taken advantage of by live migration. > > > > + If user space detects two mdev devices are compatible through version > > > > + attribute, it can start migration between the two mdev devices, otherwise it > > > > + should abort its migration attempts between the two mdev devices. > > > > > > (...) > > > _______________________________________________ > > > intel-gvt-dev mailing list > > > intel-gvt-dev@xxxxxxxxxxxxxxxxxxxxx > > > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev > > _______________________________________________ > intel-gvt-dev mailing list > intel-gvt-dev@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev
