block: add a bio_add_vmalloc helpers

Add a helper to add a vmalloc region to a bio, abstracting away the
vmalloc addresses from the underlying pages and another one wrapping
it for the simple case where all data fits into a single bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20250507120451.4000627-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1076,6 +1076,61 @@ bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
 }
 EXPORT_SYMBOL(bio_add_folio);
 
+/**
+ * bio_add_vmalloc_chunk - add a vmalloc chunk to a bio
+ * @bio: destination bio
+ * @vaddr: vmalloc address to add
+ * @len: total length in bytes of the data to add
+ *
+ * Add data starting at @vaddr to @bio and return how many bytes were added.
+ * This may be less than the amount originally asked.  Returns 0 if no data
+ * could be added to @bio.
+ *
+ * This helper calls flush_kernel_vmap_range() for the range added.  For reads
+ * the caller still needs to manually call invalidate_kernel_vmap_range() in
+ * the completion handler.
+ */
+unsigned int bio_add_vmalloc_chunk(struct bio *bio, void *vaddr, unsigned len)
+{
+	unsigned int offset = offset_in_page(vaddr);
+
+	len = min(len, PAGE_SIZE - offset);
+	if (bio_add_page(bio, vmalloc_to_page(vaddr), len, offset) < len)
+		return 0;
+	if (op_is_write(bio_op(bio)))
+		flush_kernel_vmap_range(vaddr, len);
+	return len;
+}
+EXPORT_SYMBOL_GPL(bio_add_vmalloc_chunk);
+
+/**
+ * bio_add_vmalloc - add a vmalloc region to a bio
+ * @bio: destination bio
+ * @vaddr: vmalloc address to add
+ * @len: total length in bytes of the data to add
+ *
+ * Add data starting at @vaddr to @bio.  Return %true on success or %false if
+ * @bio does not have enough space for the payload.
+ *
+ * This helper calls flush_kernel_vmap_range() for the range added.  For reads
+ * the caller still needs to manually call invalidate_kernel_vmap_range() in
+ * the completion handler.
+ */
+bool bio_add_vmalloc(struct bio *bio, void *vaddr, unsigned int len)
+{
+	do {
+		unsigned int added = bio_add_vmalloc_chunk(bio, vaddr, len);
+
+		if (!added)
+			return false;
+		vaddr += added;
+		len -= added;
+	} while (len);
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(bio_add_vmalloc);
+
 void __bio_release_pages(struct bio *bio, bool mark_dirty)
 {
 	struct folio_iter fi;

include/linux/bio.h

@@ -433,6 +433,9 @@ static inline unsigned int bio_add_max_vecs(void *kaddr, unsigned int len)
 	return 1;
 }
 
+unsigned int bio_add_vmalloc_chunk(struct bio *bio, void *vaddr, unsigned len);
+bool bio_add_vmalloc(struct bio *bio, void *vaddr, unsigned int len);
+
 int submit_bio_wait(struct bio *bio);
 int bdev_rw_virt(struct block_device *bdev, sector_t sector, void *data,
 		size_t len, enum req_op op);