target/file: allocate the bvec array as part of struct target_core_file_cmd

This saves one memory allocation, and ensures the bvecs aren't freed
before the AIO completion.  This will allow the lower level code to be
optimized so that it can avoid allocating another bvec array.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/target/target_core_file.c

@@ -241,6 +241,7 @@ struct target_core_file_cmd {
 	unsigned long	len;
 	struct se_cmd	*cmd;
 	struct kiocb	iocb;
+	struct bio_vec	bvecs[];
 };
 
 static void cmd_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
@@ -268,29 +269,22 @@ fd_execute_rw_aio(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 	struct target_core_file_cmd *aio_cmd;
 	struct iov_iter iter = {};
 	struct scatterlist *sg;
-	struct bio_vec *bvec;
 	ssize_t len = 0;
 	int ret = 0, i;
 
-	aio_cmd = kmalloc(sizeof(struct target_core_file_cmd), GFP_KERNEL);
+	aio_cmd = kmalloc(struct_size(aio_cmd, bvecs, sgl_nents), GFP_KERNEL);
 	if (!aio_cmd)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
-	bvec = kcalloc(sgl_nents, sizeof(struct bio_vec), GFP_KERNEL);
-	if (!bvec) {
-		kfree(aio_cmd);
-		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
-	}
-
 	for_each_sg(sgl, sg, sgl_nents, i) {
-		bvec[i].bv_page = sg_page(sg);
-		bvec[i].bv_len = sg->length;
-		bvec[i].bv_offset = sg->offset;
+		aio_cmd->bvecs[i].bv_page = sg_page(sg);
+		aio_cmd->bvecs[i].bv_len = sg->length;
+		aio_cmd->bvecs[i].bv_offset = sg->offset;
 
 		len += sg->length;
 	}
 
-	iov_iter_bvec(&iter, is_write, bvec, sgl_nents, len);
+	iov_iter_bvec(&iter, is_write, aio_cmd->bvecs, sgl_nents, len);
 
 	aio_cmd->cmd = cmd;
 	aio_cmd->len = len;
@@ -307,8 +301,6 @@ fd_execute_rw_aio(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 	else
 		ret = call_read_iter(file, &aio_cmd->iocb, &iter);
 
-	kfree(bvec);
-
 	if (ret != -EIOCBQUEUED)
 		cmd_rw_aio_complete(&aio_cmd->iocb, ret, 0);