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Date: Mon, 4 Dec 2017 17:29:33 +0100
From: Christoph Hellwig <hch@....de>
To: Richard Weinberger <richard@....at>
Cc: user-mode-linux-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, axboe@...com,
anton.ivanov@...bridgegreys.com, hch@....de,
linux-block@...r.kernel.org, david@...ma-star.at
Subject: Re: [PATCH] um: Convert ubd driver to blk-mq
On Sun, Dec 03, 2017 at 10:49:23PM +0100, Richard Weinberger wrote:
> Convert the driver to the modern blk-mq framework.
> As byproduct we get rid of our open coded restart logic and let
> blk-mq handle it.
>
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
> arch/um/drivers/ubd_kern.c | 178 +++++++++++++++++++++++----------------------
> 1 file changed, 93 insertions(+), 85 deletions(-)
>
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index b55fe9bf5d3e..deceb8022a28 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -23,6 +23,7 @@
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/blkdev.h>
> +#include <linux/blk-mq.h>
> #include <linux/ata.h>
> #include <linux/hdreg.h>
> #include <linux/cdrom.h>
> @@ -142,7 +143,6 @@ struct cow {
> #define MAX_SG 64
>
> struct ubd {
> - struct list_head restart;
> /* name (and fd, below) of the file opened for writing, either the
> * backing or the cow file. */
> char *file;
> @@ -156,9 +156,12 @@ struct ubd {
> struct cow cow;
> struct platform_device pdev;
> struct request_queue *queue;
> + struct blk_mq_tag_set tag_set;
> spinlock_t lock;
> +};
> +
> +struct ubd_pdu {
> struct scatterlist sg[MAX_SG];
> - struct request *request;
> int start_sg, end_sg;
> sector_t rq_pos;
> };
> @@ -182,10 +185,6 @@ struct ubd {
> .shared = 0, \
> .cow = DEFAULT_COW, \
> .lock = __SPIN_LOCK_UNLOCKED(ubd_devs.lock), \
> - .request = NULL, \
> - .start_sg = 0, \
> - .end_sg = 0, \
> - .rq_pos = 0, \
> }
>
> /* Protected by ubd_lock */
> @@ -196,6 +195,12 @@ static int fake_ide = 0;
> static struct proc_dir_entry *proc_ide_root = NULL;
> static struct proc_dir_entry *proc_ide = NULL;
>
> +static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
> + const struct blk_mq_queue_data *bd);
> +static int ubd_init_request(struct blk_mq_tag_set *set,
> + struct request *req, unsigned int hctx_idx,
> + unsigned int numa_node);
> +
> static void make_proc_ide(void)
> {
> proc_ide_root = proc_mkdir("ide", NULL);
> @@ -448,11 +453,8 @@ __uml_help(udb_setup,
> " in the boot output.\n\n"
> );
>
> -static void do_ubd_request(struct request_queue * q);
> -
> /* Only changed by ubd_init, which is an initcall. */
> static int thread_fd = -1;
> -static LIST_HEAD(restart);
>
> /* Function to read several request pointers at a time
> * handling fractional reads if (and as) needed
> @@ -510,9 +512,6 @@ static int bulk_req_safe_read(
> /* Called without dev->lock held, and only in interrupt context. */
> static void ubd_handler(void)
> {
> - struct ubd *ubd;
> - struct list_head *list, *next_ele;
> - unsigned long flags;
> int n;
> int count;
>
> @@ -532,23 +531,17 @@ static void ubd_handler(void)
> return;
> }
> for (count = 0; count < n/sizeof(struct io_thread_req *); count++) {
> - blk_end_request(
> - (*irq_req_buffer)[count]->req,
> - BLK_STS_OK,
> - (*irq_req_buffer)[count]->length
> - );
> - kfree((*irq_req_buffer)[count]);
> + struct io_thread_req *io_req = (*irq_req_buffer)[count];
> + int err = io_req->error ? BLK_STS_IOERR : BLK_STS_OK;
> +
> + if (!blk_update_request(io_req->req, err, io_req->length))
> + __blk_mq_end_request(io_req->req, err);
> +
> + kfree(io_req);
> }
> }
> - reactivate_fd(thread_fd, UBD_IRQ);
>
> - list_for_each_safe(list, next_ele, &restart){
> - ubd = container_of(list, struct ubd, restart);
> - list_del_init(&ubd->restart);
> - spin_lock_irqsave(&ubd->lock, flags);
> - do_ubd_request(ubd->queue);
> - spin_unlock_irqrestore(&ubd->lock, flags);
> - }
> + reactivate_fd(thread_fd, UBD_IRQ);
> }
>
> static irqreturn_t ubd_intr(int irq, void *dev)
> @@ -869,6 +862,7 @@ static void ubd_device_release(struct device *dev)
> struct ubd *ubd_dev = dev_get_drvdata(dev);
>
> blk_cleanup_queue(ubd_dev->queue);
> + blk_mq_free_tag_set(&ubd_dev->tag_set);
> *ubd_dev = ((struct ubd) DEFAULT_UBD);
> }
>
> @@ -911,6 +905,11 @@ static int ubd_disk_register(int major, u64 size, int unit,
>
> #define ROUND_BLOCK(n) ((n + ((1 << 9) - 1)) & (-1 << 9))
>
> +static const struct blk_mq_ops ubd_mq_ops = {
> + .queue_rq = ubd_queue_rq,
> + .init_request = ubd_init_request,
> +};
Use tables to align the "=" signs?
> + blk_mq_start_request(req);
> +
> + pdu->rq_pos = blk_rq_pos(req);
> + pdu->start_sg = 0;
> + pdu->end_sg = blk_rq_map_sg(req->q, req, pdu->sg);
>
> + if (req_op(req) == REQ_OP_FLUSH) {
> + io_req = kmalloc(sizeof(struct io_thread_req), GFP_ATOMIC);
GFP_ATOMIC in the I/O path looks scary, but it seems the existing code
already does this. Any reason not to embdedd the first one into
struct request and then use a mempool for the rest?
> + if (io_req == NULL) {
> + blk_mq_requeue_request(req, true);
> + goto done;
> }
> + prepare_flush_request(req, io_req);
> + submit_request(io_req, dev);
>
> - req = dev->request;
> + goto done;
> + }
If you only call blk_mq_start_request once everything is set up you
can just return a BLK_STS_ code from ->queue_rq.
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