On Mon, Jun 07, 2021 at 04:29:54PM +0800, Tom Yan wrote: > Hi philmd (and others), > > So I just noticed your commit of requiring the size of an emulated SD > card to be a power of 2, when I was trying to emulate one for an > actual one (well, it's a microSD, but still), as it errored out. > > You claim that the kernel will consider it to be a firmware bug and > "correct" the capacity by rounding it up. Could you provide a concrete > reference to the code that does such a thing? I'm not ruling out that > some crazy code could have gone upstream because some reviewers might > not be doing their job right, but if that really happened, it's a > kernel bug/regression and qemu should not do an equally-crazy thing to > "fix" it.
I looked back at the original threads for details, but didn't find any aside from this short message saying it broke Linux: https://www.mail-archive.com/qemu-devel@nongnu.org/msg720737.html Philippe, do you have more details on the problem hit, or pointer to where the power-of-2 restriction is in Linux ? > No offense but what you claimed really sounds absurd and ridiculous. > Although I don't have hundreds of SD cards in hand, I owned quite a > few at least, like most people do, with capacities ranging from ~2G to > ~128G, and I don't even recall seeing a single one that has the > capacity being a power of 2. (Just like vendors of HDDs and SSDs, they > literally never do that AFAICT, for whatever reasons.) Yes, this does feel pretty odd to me too, based on the real physical SD cards I've used with Linux non-power-2 sizes. Also in general QEMU shouldn't be enforcing restrictions based on guest behaviour, it should follow the hardware specs. If the hardware spec doesn't mandate power-of-2 sizes, then QEMU shoud not require that, even if some guest OS has added an artificial restriction of its own. > Besides, even if there's a proper reason for the kernel to "fix" the > capacity, there's no reason for it to round it up either, because > obviously there will never be actual storage for the "virtual blocks". > I've never seen such a behavior so far either with the "mmcblk" hosts > I've used so far. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
