On Sunday 20 March 2011, MichaÅ MirosÅaw wrote: > 2011/3/20 John Calixto <john.calixto@xxxxxxxxxxxxxx>: > > On Sat, 19 Mar 2011, Arnd Bergmann wrote: > [...] > >> > I expect for more general purposes, like your qemu passthrough case, you > >> > would want to add a handler for cmd=SD_IOC_CMD? > >> Yes, but I suspect that would mean blocking all other activity on the > >> same device, possibly with an ioctl for claiming the host for an > >> extended period of time. > > Sure. And if the testing I described above shows that regular block > > operations are indeed negatively affected, then I'll have to implement > > that ioctl for claiming the host myself and you'll have a head start! :) > > This idea is scary. ;-) Just think what would happen if userspace made > this sequence: > 1. fd = open(dev) > 2. ioctl(fd, claim host) > 3. read(fd, ...) > > (if 3. is not convincing, replace it with any access to mounted > filesystem from the same card.) I agree. If we allow such a command on a block device, that should probably be mutually exclusive with normal read/write access or mounting the block device, and it needs to be a priviledged operation. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
