On Mon, Jun 7, 2021 at 2:31 AM Tom Yan <tom.t...@gmail.com> 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. > > 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.) > > 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. >
Some data points: I have several 224GB SD cards. FreeBSD specifically uses a size just a little smaller than the rated size because so many capacity points are a bit smaller (1GB cards also tend to be only 1% larger 1E9 bytes, nowhere near a power of two). FreeBSD's kernel never adjusts the size of SD or MMC cards, and there's nothing in the Simplified SD standard nor in the various MMC standards requiring a power of two. Warner
