Add a function to kmap one page of a multipage bio_vec by offset (which is added to the offset in the bio_vec internally). The caller is responsible for calculating how much of the page is then available. Signed-off-by: David Howells Acked-by: Paulo Alcantara (Red Hat) cc: Matthew Wilcox cc: Christoph Hellwig cc: Jens Axboe cc: linux-block@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- include/linux/bvec.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/linux/bvec.h b/include/linux/bvec.h index d36dd476feda..f834a862224e 100644 --- a/include/linux/bvec.h +++ b/include/linux/bvec.h @@ -299,4 +299,22 @@ static inline phys_addr_t bvec_phys(const struct bio_vec *bvec) return page_to_phys(bvec->bv_page) + bvec->bv_offset; } +/** + * bvec_kmap_partial - Map part of a bvec into the kernel virtual address space + * @bvec: bvec to map + * @offset: Offset into bvec + * + * Map the page containing the byte at @offset into the kernel virtual address + * space. The caller is responsible for making sure this doesn't overrun. + * + * Call kunmap_local on the returned address to unmap. + */ +static inline void *bvec_kmap_partial(struct bio_vec *bvec, size_t offset) +{ + offset += bvec->bv_offset; + + return kmap_local_page(bvec->bv_page + (offset >> PAGE_SHIFT)) + + (offset & ~PAGE_MASK); +} + #endif /* __LINUX_BVEC_H */