As I said - I think it would be better to remove the immutable flag than
to create more flags to bypass it.
Mikulas
On Wed, 28 Aug 2013, Mike Snitzer wrote:
> Introduce DM_TARGET_ALWAYS_RETURNS_IO_ERROR to indicate that a target
> always returns IO error. Because the target will error all IO it can
> safely replace any target (including an immutable target) as along as
> the associated mapped device is not open. If an error target replaces
> an immutable target it is elevated to the mapped device's immutable
> target type.
>
> The "error" target can now replace an immutable target like the thin
> provisioning pool ("thin-pool") target.
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> drivers/md/dm-ioctl.c | 27 ++++++++++++++++++++++++++-
> drivers/md/dm-table.c | 9 ++++++++-
> drivers/md/dm-target.c | 1 +
> include/linux/device-mapper.h | 10 ++++++++++
> 4 files changed, 45 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 301e0a5..08186cb 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1248,6 +1248,30 @@ static int populate_table(struct dm_table *table,
> return dm_table_complete(table);
> }
>
> +static bool immutable_target_type_is_valid(struct mapped_device *md,
> + struct target_type *immutable_tt,
> + struct target_type *table_immutable_tt)
> +{
> + if (immutable_tt == table_immutable_tt)
> + return true;
> +
> + if (!table_immutable_tt)
> + return false;
> +
> + if (dm_target_always_returns_io_error(table_immutable_tt)) {
> + /*
> + * Only allow a transition to an error target_type if
> + * the mapped_device is no longer open.
> + */
> + if (!dm_open_count(md))
> + return true;
> +
> + DMERR("can't change target type to error while device is in use");
> + }
> +
> + return false;
> +}
> +
> static int table_load(struct dm_ioctl *param, size_t param_size)
> {
> int r;
> @@ -1272,7 +1296,8 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
>
> immutable_target_type = dm_get_immutable_target_type(md);
> if (immutable_target_type &&
> - (immutable_target_type != dm_table_get_immutable_target_type(t))) {
> + !immutable_target_type_is_valid(md, immutable_target_type,
> + dm_table_get_immutable_target_type(t))) {
> DMWARN("can't replace immutable target type %s",
> immutable_target_type->name);
> r = -EINVAL;
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 8f87835..70d3067 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -745,7 +745,14 @@ int dm_table_add_target(struct dm_table *t, const char *type,
> return -EINVAL;
> }
>
> - if (t->immutable_target_type) {
> + if (dm_target_always_returns_io_error(tgt->type) &&
> + dm_get_immutable_target_type(t->md)) {
> + /*
> + * This error target must be upgraded to immutable because
> + * the mapped device is already using an immutable target.
> + */
> + t->immutable_target_type = tgt->type;
> + } else if (t->immutable_target_type) {
> if (t->immutable_target_type != tgt->type) {
> DMERR("%s: immutable target type %s cannot be mixed with other target types",
> dm_device_name(t->md), t->immutable_target_type->name);
> diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
> index 242e3ce..3b9a988 100644
> --- a/drivers/md/dm-target.c
> +++ b/drivers/md/dm-target.c
> @@ -139,6 +139,7 @@ static int io_err_map_rq(struct dm_target *ti, struct request *clone,
>
> static struct target_type error_target = {
> .name = "error",
> + .features = DM_TARGET_ALWAYS_RETURNS_IO_ERROR,
> .version = {1, 2, 0},
> .ctr = io_err_ctr,
> .dtr = io_err_dtr,
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 653073d..2451e6b 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -192,6 +192,16 @@ struct target_type {
> #define dm_target_is_immutable(type) ((type)->features & DM_TARGET_IMMUTABLE)
>
> /*
> + * Indicates that a target always returns IO error. Because the target will error
> + * all IO it can safely replace any target (including an immutable target) as long
> + * as the associated mapped device is not open. If an error target replaces an
> + * immutable target it is elevated to the mapped device's immutable target type.
> + */
> +#define DM_TARGET_ALWAYS_RETURNS_IO_ERROR 0x00000008
> +#define dm_target_always_returns_io_error(type) \
> + ((type)->features & DM_TARGET_ALWAYS_RETURNS_IO_ERROR)
> +
> +/*
> * Some targets need to be sent the same WRITE bio severals times so
> * that they can send copies of it to different devices. This function
> * examines any supplied bio and returns the number of copies of it the
> --
> 1.8.1.4
>
> --
> dm-devel mailing list
> dm-devel@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/dm-devel
>
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