On Thu, Dec 09, 2010 at 04:25:35PM +0100, Lukas Czerner wrote: > Hi all, > > For a long time it has been pretty painful to retrieve informations from > /sys/block/*/queue for particular block device. Not only it is painful > to retrieve informations within C tool, parsing strings, etc, but one > have to run into problem even finding the proper path in sysfs. What's wrong with using libudev? That should give you all of this information easily using a .c program without any need to change the kernel at all. > This patch set adds new block ioctl BLKGETQUEUEINFO, which is designed to > retrieve particular block queue attributes. I have tried to not to > create completely new interface, but since we already have those > information within block queue sysfs kobjects, rather retrieve it from > there. Ick, no, please just use the sysfs files, don't create a new ioctl, they are horrid. > > So it binds enum blkq_info_type in include/linux/fs.h with > default_attrs[] definition within block/blk-sysfs.c for ordering > purposes, so the userspace has reliable way to address specific > block queue attribute. > > In order to avoid string parsing (given that 99% of block queue sysfs > attributes are of unsigned long type) I have introduced new sysfs_ops > member *get which may be used to pass pointer to any type of data (unsigned > long in this case). Then this get method is used to withdraw information > through kobject->ktype->sysfs_ops. > > Although there are some downsides of this approach I would like to discuss: > > 1. In current state BLKGETQUEUEINFO and the whole infrastructure allow to > retrieve only numeric values (no text), this means we are no able to > retrieve schedule information. > > 2. Adding new *get member into sysfs_ops. I see this as the most painful > downside, however, when we have more subsystems adding ioctls like this, > they can easily use this method, the same way I am using it now. Nope, don't do this, just use sysfs how it is supposed to be used, from userspace. sorry, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
