On Tue, Oct 18, 2016 at 4:24 PM, Ed Bartosh <ed.bart...@linux.intel.com> wrote: > On Tue, Oct 18, 2016 at 03:59:23PM +0200, Maciej Borzęcki wrote: >> >> >> >> > What's the advantage of creating unusable gap over creating >> >> >> >> > partition of >> >> >> >> > the same size that can be used? >> >> >> >> >> >> >> >> Just convenience. >> >> >> >> >> >> >> > What's the convenience of having extra space on partition that can't >> >> >> > be >> >> >> > used for data over having it formatted and used? >> >> >> > >> >> >> >> > Even if that space is not needed it doesn't harm to have it, does >> >> >> >> > it? >> >> >> >> >> >> >> >> I have not seen any negative side effects. >> >> >> >> >> >> >> > I do. If user needs that reserved space it's impossible to get it >> >> >> > without >> >> >> > reformatting partition. The free space exists, but can't be used. >> >> >> >> >> >> That's not the point and is not aligned with use case I'm trying to >> >> >> solve. >> >> >> >> >> >> My case is rather simple, I'm creating an image for SD card that is >> >> >> deployed in the field. In that particular case, there's a primary and >> >> >> a secondary (aka. active and inactive) rootfs partitions that are >> >> >> switched whenever a system update comes in. The update is a file >> >> >> system image that is copied over to the inactive partition, followed >> >> >> by a system reboot. >> >> >> >> >> >> What I need is the ability to set a certain size of a partition (say >> >> >> 100MB), regardless of current rootfs size (which may be, say 70MB). >> >> >> The remaining unused space sets an upper limit on how much the rootfs >> >> >> may grow in the future (in this example case, it's 30MB). RIght now >> >> >> the best I can do is to describe a partition like this: `part / >> >> >> --source rootfs --size 100MB --overhead-factor 1`, hoping that if >> >> >> rootfs grows beyond 100MB I will somehow still be able to catch that >> >> >> and that the future images remain size compatible. >> >> >> >> >> >> The resulting filesystem inside the partition is larger than what >> >> >> IMAGE_CMD (ex. IMAGE_CMD_ext4) would give me, because of explicit >> >> >> --size in kickstart. I would prefer to have something comparable in >> >> >> size just to avoid later surprises, what implies using defaults. >> >> >> However, using defaults, means that I cannot control the layout >> >> >> because it will likely change each time rootfs size gets changed. >> >> >> There is no `--fixed-size` or other option to enforce specific size. >> >> >> >> >> >> Summing up, a simple use case that cannot be currently solved using >> >> >> wic. >> >> >> >> >> >> BTW. actually we're missing an ability to enforce --size (i.e. >> >> >> --fixed-size?) and a method passing an explicit partition offset >> >> >> inside the disk image (something useful for `--source rawcopy >> >> >> --no-table` partitions, currently solved with `--align`). >> >> >> >> >> > I undertood the problem and I agree that wic doesn't provide a solution. >> >> > >> >> > However, instead of making unformatted space I'd propose to format it, >> >> > i.e. to have --max-size option that would confict with --size and >> >> > specify upper size limit for the partition. All partition will be >> >> > formatted and available for data. This is identical to --fixed-size >> >> > option >> >> > you've described. This approach would solve the problem you're >> >> > addressing and it would also make additional space usable. >> >> > >> >> > I'd also suggest to rename --size to --min-size and make --size >> >> > deprecated. >> >> > >> >> > Does this make sense to you? >> >> >> >> No strong opinions here, just that deprecating --size might current >> >> users uneasy. >> >> >> > By deprecting --size I didn't mean removing it completely. We can just >> > print a warning suggesting usage of other options. >> > >> >> Perhaps --max-size could be a boolean switch? We could just name it >> >> --fixed-size (bool, defaults to False), with semantics that if >> >> --fixed-size is provided, the partition will have size --size, >> >> occurrence of --overhead-factor or --extra-space will raise an error. >> >> >> > That would work too, but it looks a bit confusing to me to have 2 different >> > types of size-related options. >> >> Ok, but now we would have --min-size (previously known as --size) and >> --size (or --max-size?). That's still 2 size related options plus a >> deprecation warning. >> > > I agree, it doesn't look good. Moreover --max-size doesn't make it > clear that partition will be this size. It rather suggests that partition > can be this size or less. > > So, we have --size which is actually minimum partition size, we have > couple of options to extend partition size (--overhead-factor and > --extra-space), but we don't have ability to set upper limit for partition > size. > > OK, let's agree on using --fixed-size(int) > Using --fixed-size with any of --size or --overhead-factor or --extra-space > options should raise ks parser error. If rootfs size is bigger than > --fixed-size wic should raise an error too. > > Any other opinions?
Sounds good. I'll try to post a patch in the next couple of days. Cheers, -- Maciej Borzecki RnDity -- _______________________________________________ Openembedded-core mailing list Openembedded-core@lists.openembedded.org http://lists.openembedded.org/mailman/listinfo/openembedded-core