Nack. I'm not building a linear target into every other target. Layering
targets is simple.
On Tue, Feb 7, 2023 at 7:56 AM Demi Marie Obenour <
d...@invisiblethingslab.com> wrote:
> This allows exposing only part of a thin volume without having to layer
> dm-linear. One use-case is a hypervisor replacing a partition table.
>
> Signed-off-by: Demi Marie Obenour <d...@invisiblethingslab.com>
> ---
> drivers/md/dm-thin.c | 32 ++++++++++++++++++++++++++------
> 1 file changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index
> d85fdbd782ae5426003c99a4b4bf53818cc85efa..87f14933375b050a950a5f58e98c13b4d28f6af0
> 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
> @@ -357,6 +357,7 @@ struct thin_c {
> */
> refcount_t refcount;
> struct completion can_destroy;
> + u64 offset;
> };
>
> /*----------------------------------------------------------------*/
> @@ -1180,9 +1181,9 @@ static void
> process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m)
> discard_parent = bio_alloc(NULL, 1, 0, GFP_NOIO);
> discard_parent->bi_end_io = passdown_endio;
> discard_parent->bi_private = m;
> - if (m->maybe_shared)
> - passdown_double_checking_shared_status(m, discard_parent);
> - else {
> + if (m->maybe_shared)
> + passdown_double_checking_shared_status(m, discard_parent);
> + else {
> struct discard_op op;
>
> begin_discard(&op, tc, discard_parent);
> @@ -4149,7 +4150,7 @@ static int thin_ctr(struct dm_target *ti, unsigned
> argc, char **argv)
>
> mutex_lock(&dm_thin_pool_table.mutex);
>
> - if (argc != 2 && argc != 3) {
> + if (argc < 2 || argc > 4) {
> ti->error = "Invalid argument count";
> r = -EINVAL;
> goto out_unlock;
> @@ -4168,7 +4169,8 @@ static int thin_ctr(struct dm_target *ti, unsigned
> argc, char **argv)
> bio_list_init(&tc->retry_on_resume_list);
> tc->sort_bio_list = RB_ROOT;
>
> - if (argc == 3) {
> + /* Use "/" to indicate "no origin device" while providing an
> offset */
> + if (argc >= 3 && strcmp(argv[2], "/")) {
> if (!strcmp(argv[0], argv[2])) {
> ti->error = "Error setting origin device";
> r = -EINVAL;
> @@ -4196,6 +4198,23 @@ static int thin_ctr(struct dm_target *ti, unsigned
> argc, char **argv)
> goto bad_common;
> }
>
> + tc->offset = 0;
> + if (argc > 3) {
> + sector_t sector_offset;
> +
> + if (kstrtoull(argv[3], 10, &tc->offset)) {
> + ti->error = "Invalid offset";
> + r = -EINVAL;
> + goto bad_common;
> + }
> +
> + if (check_add_overflow(tc->offset, ti->len,
> §or_offset)) {
> + ti->error = "Offset + len overflows sector_t";
> + r = -EINVAL;
> + goto bad_common;
> + }
> + }
> +
> pool_md = dm_get_md(tc->pool_dev->bdev->bd_dev);
> if (!pool_md) {
> ti->error = "Couldn't get pool mapped device";
> @@ -4285,8 +4304,9 @@ static int thin_ctr(struct dm_target *ti, unsigned
> argc, char **argv)
>
> static int thin_map(struct dm_target *ti, struct bio *bio)
> {
> - bio->bi_iter.bi_sector = dm_target_offset(ti,
> bio->bi_iter.bi_sector);
> + struct thin_c *tc = ti->private;
>
> + bio->bi_iter.bi_sector = dm_target_offset(ti,
> bio->bi_iter.bi_sector) + tc->offset;
> return thin_bio_map(ti, bio);
> }
>
> --
> Sincerely,
> Demi Marie Obenour (she/her/hers)
> Invisible Things Lab
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://listman.redhat.com/mailman/listinfo/dm-devel
>
>
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