On Tue, Oct 18, 2016 at 11:24:14AM +0200, Maciej Borzęcki wrote: > On Tue, Oct 18, 2016 at 10:38 AM, Ed Bartosh <ed.bart...@linux.intel.com> > wrote: > > On Tue, Oct 18, 2016 at 10:37:22AM +0200, Maciej Borzęcki wrote: > >> On Tue, Oct 18, 2016 at 9:31 AM, Ed Bartosh <ed.bart...@linux.intel.com> > >> wrote: > >> > On Mon, Oct 17, 2016 at 04:46:00PM +0200, Maciej Borzęcki wrote: > >> >> On Mon, Oct 17, 2016 at 3:22 PM, Ed Bartosh > >> >> <ed.bart...@linux.intel.com> wrote: > >> >> > Hi Maciej, > >> >> > > >> >> > There is already --size and --extra-space options. > >> >> > Can we get the same or similar result by just using them? Do we really > >> >> > need new option for similar purpose? > >> >> > >> >> --reserved-size serves a different purpose, it establishes an upper > >> >> bound on the size of a partition during layout. Unlike > >> >> --size/--extra-space does not depend on the size of the filesystem > >> >> image. > >> >> > >> >> For instance, assume I'm creating an image for SD card/eMMC with a > >> >> fixed partition layout (something simple: boot partition, primary & > >> >> secondary rootfs partitions, some data partition). Because future > >> >> system updates are delivered as filesystem image, I want to make sure > >> >> that there is exactly xxx MBs for my current and future rootfs images > >> >> (regardless of current image size). Neither --size nor --extra-space > >> >> can do that. I could use, say `--size 200 --overhead-factor 1`, but > >> >> this will needlessly create a 200MB rootfs image and if I happen to > >> >> cross the 200MB boundary I will not get an error. > >> >> > >> >> I had a private patch that added --fixed-size to enforce --size, but > >> >> that would still end up creating filesystem image to fill the whole > >> >> space. > >> > I didn't get the difference between enforcing partition size and below > >> > implementation. Can you elaborate a bit? > >> > >> `--fixed-size` was something that I had added to my fork back in 2014, > >> even before `--overhead-factor` came in. The problem is that depending > >> on a project you might want to have more control over how partitions > >> are laid out, or even need to have a fixed layout. Adding > >> `--fixed-size` would had a similar effect to what `--overhead-factor > >> 1` does right now. Combined with `--size` would ensure that rootfs is > >> say, 200MB large. The downside was that wic would actually create a > >> 200MB rootfs, something that is not really necessary. In fact, I only > >> wanted to have 200MB gap so that I have some spare space for future > >> updates (where update is just a rootfs image you dd to the partition). > >> > > Thanks for the explanations. Now I got it - reserved size is not a part > > of partition, it's a gap between partitions. > > I might have not been clear enough when explaining. It's not a gap, > it's just a container of size --reserved-size listed in MBR/GPT. > There's probably a filesystem inside but not necessarily. > Graphically it looks as like this: > > --reserved-size > |----------------------| > v v > +-----------------+----------------------+---------------------+ > |..... stuff .....|xxxxxxxxxx |..... stuff .........| > +-----------------+----------------------+---------------------+ > ^ ^ ^ > |---------|------------| > --size --extra-space > > Ah, I'm wrong again. It's a partition size limit, but it's not necessary formatted, right? It's only formatted if size == reserved_size.
> > > > 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. -- Regards, Ed -- _______________________________________________ Openembedded-core mailing list Openembeddedfirstname.lastname@example.org http://lists.openembedded.org/mailman/listinfo/openembedded-core