On Thu, Nov 10, 2022 at 01:52:43AM +0000, Daniel Golle wrote: > On Wed, Nov 09, 2022 at 05:21:01PM +0000, Matthew Wilcox wrote: > > On Wed, Nov 09, 2022 at 02:36:11PM +0000, Daniel Golle wrote: > > > On Wed, Nov 09, 2022 at 01:58:29PM +0000, Matthew Wilcox wrote: > > > > ... actually, why can't you call read_part_sector() and avoid all of > > > > this? > > > > > > I've tried that before and the problem is that read_part_sector() > > > returns a pointer to one sector (typically 512 bytes) of data. > > > And this pointer should not be accesses beyond sector boundaries, > > > right? You'd have to call read_part_sector() again for the next > > > sector. > > > > > > The FIT structure, however, usually exceeds the size of one sector, > > > and having a continous memory area covering the structure as a whole > > > is crucial for libfdt to do its job. > > > > > > I could, of course, use read_part_sector() to copy all sectors > > > covering the FIT structure into a buffer, but that seemed strange > > > given that read_part_sector() actually used read_mapping_page() > > > (and now uses read_mapping_folio()) internally and then returns a > > > pointer to the offset within the page/folio. So why not read it in one > > > piece in first place instead of having it first split up to sectors > > > by read_part_sector() just to then having to reassemble it into a > > > continous buffer again. > > > > Are you guaranteed that it's "sufficiently" aligned on storage so > > that it fits entirely within a single page? If not, you'll have > > to copy it, vmap it, or fix libfdt to handle a segmented buffer. > > Yes, for the uImage.FIT to be usable for the partition parser it has > to be page-aligned. > > There is a check which makes sure that this is the case: > > + /* uImage.FIT should be aligned to page boundaries */ > > + if (fit_start_sector % (1 << (PAGE_SHIFT - SECTOR_SHIFT))) > > + return 0; > > In case of mtdblock or ubiblock devices, the image always starts at > offset 0, so this is never a problem. > In case of the image being stored in a GPT partition, one has to make > sure that the start sector of the partition is page aligned, otherwise > the above check will fail and the partition parser will bail out. OK. Then I think open coding it is the right idea, just with all the cruft removed ;-) I looked at extracting parts of read_part_sector() into read_part_page(), but it ended up being a two line function that wasn't terribly useful.
