Re: [PATCH v3 bpf-next 02/10] lib/buildid: add single page-based file reader abstraction

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On Wed, Aug 07, 2024 at 04:28:53PM GMT, Matthew Wilcox wrote:
> On Tue, Jul 30, 2024 at 01:39:06PM -0700, Andrii Nakryiko wrote:
> > +	union {
> > +		struct {
> > +			struct address_space *mapping;
> > +			struct page *page;
> 
> NAK.  All the page-based interfaces are deprecated.  Only we can't mark
> them as deprecated because our tooling is a pile of crap.
> 
> > +			void *page_addr;
> > +			u64 file_off;
> 
> loff_t pos.
> 
> > +	r->page = find_get_page(r->mapping, pg_off);
> 
> r->folio = read_mapping_folio(r->mapping, r->pos / PAGE_SIZE, ...)
> 
> OK, for network filesystems, you're going to need to retain the struct
> file that's used to access them.  So maybe this becomes
> 	read_mapping_folio(r->file->f_mapping, r->pos, r->file)

This code path can be called from non-sleepable context. What would be
the appropriate way to get the folio in that case?

> 
> > +	r->page_addr = kmap_local_page(r->page);
> 
> kmap_local_folio(r->folio, offset_in_folio(r->folio, r->pos));
> 




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