On Wed, Apr 6, 2016 at 9:05 AM, Zheng, Lv <lv.zheng@xxxxxxxxx> wrote: >> It is hard to create new kernel objects from sysfs. You need to resort >> to hacks like using new_table sysfs entries which does not map to a >> kernel object. Writes larger then PAGE_SIZE are impossible to handle >> with multiple open files because you have no open callback to create a >> file context. It is also not possible to do any clean-up because there >> is no close callback and if something goes wrong for example when >> trying to install the table you will leak the allocated memory. >> >> configfs was designed for the specific purpose of creating kernel >> objects from userspace and addresses all of the limitations above (and >> some more). >> >> Initially I started to implement this functionality via sysfs but I >> run into the issues mentioned above and decided to use configfs. > [Lv Zheng] > I can sense different difficulties from your descriptions. > Let me break it down into details. > > We already have acpi_table_handler working there for creating new ACPI table entries for us. > Based on this facility, let's think about the following solution: > 1. sysfs presenting change > We can change the table file to a table directory whose name is in the following format: > TableSignature-OemId-OemTableId > Then we can get rid of the annoying numbered table name suffix first. > The numbered table name suffix cannot be kept consistent to reflect the real index if we allow tables to be dynamically loaded/unloaded. > > This is the first design difficulty we need to solve. > > 2. acpi_table_handler change > Now we can append 2 new events to acpi_table_handler - ACPI_TABLE_INSTALL/ACPI_TABLE_UNINSTALL. > With which, the sysfs entries can be created/deleted when the table is added to/removed from the global table list. > And this should be the working mechanism for us > So we actually don't have the trouble to deal with the new kernel object creation/deletion from sysfs. > > I agree the dynamic kernel object creation/deletion need special care. > But this actually is what a kernel engineer should do because this kind of things happen here and there throughout the kernel. > We should have already been used to that. > > This is the second engineering difficulty we need to face. > > 3. load/unload commanding > Now we need a character device in sysfs to handle load/unload command. > Well, there are many such kind of files in sysfs, for example, device nodes. > So this is not a non-achievable task, but just a difficult engineering task. > The system engineers need to be skillful enough to implement this. > Like the dynamic kernel object handling, we should have already been used to this. > > > If you still think this is difficult, the alternative choice is to use acpidbg char device's ioctl interface. > That could simplifies this task. > And since the ioctl interface is required by ACPICA disassembler, the work on that will be inherited by the disassembler porting. > Why can't the dissembler access the tables through the existing sysfs interface? > This is the last engineering difficulty we need to face. > > So why can't these solutions work for us? > It can be done, but it is not the right way to do it, IMO. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
