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block: Document the bio_vec properties
Since it is nontrivial that nth_page() does not have to be used for a bio_vec, document this. Signed-off-by: Bart Van Assche <bvanassche@acm.org> Reviewed-by: Christoph Hellwig <hch@lst.de> CC: Christoph Hellwig <hch@infradead.org> Cc: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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#include <linux/errno.h>
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#include <linux/mm.h>
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/*
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* was unsigned short, but we might as well be ready for > 64kB I/O pages
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/**
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* struct bio_vec - a contiguous range of physical memory addresses
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* @bv_page: First page associated with the address range.
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* @bv_len: Number of bytes in the address range.
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* @bv_offset: Start of the address range relative to the start of @bv_page.
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*
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* The following holds for a bvec if n * PAGE_SIZE < bv_offset + bv_len:
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*
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* nth_page(@bv_page, n) == @bv_page + n
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*
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* This holds because page_is_mergeable() checks the above property.
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*/
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struct bio_vec {
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struct page *bv_page;
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