On Tue, 05 Aug 2008 02:45:16 +0100 David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote:
> On Sat, 2008-07-26 at 13:02 -0700, Andrew Morton wrote:
> > I seem to be hearing a lot of silence over support for SSD devices. I
> > have this vague worry that there will be a large rollout of SSD
> > hardware and Linux will be found to have pants-around-ankles.
> >
> > For example, support for the T13 Trim command. There will be others,
> > but I surely don't know what they are.
>
> Here's a first attempt at that. It implements basic support for
> 'discard' requests in the block layer, implements that in FTL (the flash
> translation layer used on PCMCIA flash cards), and in FAT.
Looks nice and simple.
>
> ...
>
> +int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> + unsigned nr_sects, sector_t *error_sector)
> +{
> + DECLARE_COMPLETION_ONSTACK(wait);
> + struct request_queue *q;
> + struct bio *bio;
> + int ret;
> +
> + if (bdev->bd_disk == NULL)
> + return -ENXIO;
> +
> + q = bdev_get_queue(bdev);
> + if (!q)
> + return -ENXIO;
> +
> + bio = bio_alloc(GFP_KERNEL, 0);
> + if (!bio)
> + return -ENOMEM;
> +
> + bio->bi_end_io = bio_end_empty_barrier;
> + bio->bi_private = &wait;
> + bio->bi_bdev = bdev;
> + bio->bi_sector = sector;
> + bio->bi_size = nr_sects << 9;
> + submit_bio(1 << BIO_RW_DISCARD, bio);
> +
> + wait_for_completion(&wait);
The synchronous nature might get pretty painful, even after merging is
working?
err, actually, it'll have to become async to be able to merge, won't it?
> + /*
> + * The driver must store the error location in ->bi_sector, if
> + * it supports it. For non-stacked drivers, this should be copied
> + * from rq->sector.
> + */
> + if (error_sector)
> + *error_sector = bio->bi_sector;
> +
> + ret = 0;
> + if (bio_flagged(bio, BIO_EOPNOTSUPP))
> + ret = -EOPNOTSUPP;
> + else if (!bio_flagged(bio, BIO_UPTODATE))
> + ret = -EIO;
> +
> + bio_put(bio);
> + return ret;
> +}
> +EXPORT_SYMBOL(blkdev_issue_discard);
>
> ...
>
> @@ -1411,6 +1421,10 @@ end_io:
> err = -EOPNOTSUPP;
> goto end_io;
> }
> + if (bio_discard(bio) && !q->discard_fn) {
> + err = -EOPNOTSUPP;
> + goto end_io;
> + }
>
> ret = q->make_request_fn(q, bio);
> } while (ret);
> @@ -1488,7 +1502,7 @@ void submit_bio(int rw, struct bio *bio)
> * If it's a regular read/write or a barrier with data attached,
> * go through the normal accounting stuff before submission.
> */
> - if (!bio_empty_barrier(bio)) {
> + if (!bio_empty_barrier(bio) && !bio_discard(bio)) {
Perhaps we should have a new bio_doesnt_have_any_data_in_it() helper,
rather than opn-coding it here? Assuming that new non-data-containing
bios will turn up in the future.
>
> BIO_BUG_ON(!bio->bi_size);
> BIO_BUG_ON(!bio->bi_io_vec);
> @@ -1562,13 +1576,12 @@ static int __end_that_request_first(struct request *req, int error,
> int nbytes;
>
> /*
> - * For an empty barrier request, the low level driver must
> - * store a potential error location in ->sector. We pass
> - * that back up in ->bi_sector.
> + * For an empty barrier request or sector discard request, the
> + * low level driver must store a potential error location in
> + * ->sector. We pass that back up in ->bi_sector.
> */
> - if (blk_empty_barrier(req))
> + if (blk_empty_barrier(req) || blk_discard_rq(req))
Maybe ditto.
> bio->bi_sector = req->sector;
> -
> if (nr_bytes >= bio->bi_size) {
> req->bio = bio->bi_next;
> nbytes = bio->bi_size;
>
> ...
>
>
> +static int ftl_discardsect(struct mtd_blktrans_dev *dev,
> + unsigned long sector, unsigned nr_sects)
> +{
> + partition_t *part = (void *)dev;
wuh? We're casting a `struct mtd_blktrans_ops *' into a partition_t?
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