Arnd Bergmann wrote: > On Sunday 29 April 2007, Heiko Carstens wrote: > > >>> Is this data structure extensible? If it is, you probably need >>> some sort of versioning information to make sure that user space >>> doesn't rely on fields that the kernel doesn't know about. >>> >> I don't think we can put in some versioning information here. If >> the kernel decides to increase the version then old userspace >> code would break? >> We rather need some mechanism so userpace can ask the kernel >> "do you support feature x?" and dependent on the answer some >> fields are used or unused. >> > > You could do it the way that ext2 handles compatible and incompatible > features in the on-disk layout: > > Assign a number of bits in the read-only part of the mapping to flags > that the user application can test. A bit in the compatible range mean > that a feature is available to the user application if it wants to > use it. A bit in the incompatible range means that the user space needs > to understand how to use a feature in order to run correctly. >
The current ioctl() interface has a feature test call, basically you send down a feature number get see if it's supported or not. Fairly similar to feature bit except it isn't limited in the number of bits. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
