On Mon, Nov 10, 2025 at 2:42 PM Markus Armbruster <[email protected]> wrote: > > Clément Chigot <[email protected]> writes: > > > On Mon, Nov 10, 2025 at 2:09 PM Markus Armbruster <[email protected]> wrote: > >> > >> Clément Chigot <[email protected]> writes: > >> > >> > On Mon, Nov 10, 2025 at 11:13 AM Markus Armbruster <[email protected]> > >> > wrote: > >> >> > >> >> Clément Chigot <[email protected]> writes: > >> >> > >> >> > This allows more flexibility to vvfat backend. The values of "Number > >> >> > of > >> >> > Heads" and "Sectors per track" are based on SD specifications Part 2. > >> >> > > >> >> > Due to the FAT architecture, not all sizes are reachable. Therefore, > >> >> > it > >> >> > could be round up to the closest available size. > >> >> > > >> >> > FAT32 has not been adjusted and thus still default to 504 Mib. > >> >> > > >> >> > For floppy, only 1440 Kib and 2880 Kib are supported. > >> >> > > >> >> > Signed-off-by: Clément Chigot <[email protected]> > >> >> > >> >> [...] > >> >> > >> >> > diff --git a/qapi/block-core.json b/qapi/block-core.json > >> >> > index 8a479ba090..0bcb360320 100644 > >> >> > --- a/qapi/block-core.json > >> >> > +++ b/qapi/block-core.json > >> >> > @@ -3478,11 +3478,17 @@ > >> >> > # (default: true) > >> >> > # (since 10.2) > >> >> > # > >> >> > +# @fat-size: size of the device in bytes. Due to FAT underlying > >> >> > +# architecture, this size can be rounded up to the closest valid > >> >> > +# size. > >> >> > +# (since 10.2) > >> >> > +# > >> >> > >> >> Can you explain again why you moved from @size to @fat-size? > >> > > >> > Just to be sure, you mean in the above comment, in the commit message or > >> > both ? > >> > >> Just to me, because I'm not sure I like the change, but that may well be > >> due to a lack of understanding of your reasons. > > > > Naming `fat-size` instead of `size` ensures the parameter is only > > recognized by the vvfat backend. In particular, it will be refused by > > the default raw format, avoiding confusion: > > "-drive file=fat:<path>,size=256M" results in a 504M FAT disk > > truncated to 256M, raw format being implicit. > > "-drive file=fat:<path>,fat-size=256M" is refused. "fat-size" is > > unsupported by raw format. > > I figure throwing in format=raw to make raw format explicit doesn't > change anything. Correct? > > > "-drive file=fat:<path>,format=vvfat,fat-size=256M" results in a 256M FAT > > disk. > > "-drive file=fat:<path>,format=vvfat,size=256M" is refused. "size" is > > unsupported by vvfat format. > > If it was called @size, what behavior would we get? Just two cases, I > think: > > 1. With raw format: > > -drive file=fat:<path>,size=256M > > 2. Without raw format: > > -drive file=fat:<path>,format=vvfat,size=256M
Yes and both result in a FAT system having different sizes. The only difference being "format=vvfat". When @size is renamed @fat-size, you are certain to get an error when forgetting that format=vvfat. Moreover, one could think that one day, `format=vvfat,size=256M,fat-size=128M` could coexist, creating a 256M disk with a 128M FAT partition. Again, I'm not against renaming @size, but I like Kevin's idea to avoid confusing errors just because you forgot "format".
